All posts by Urban Ag, Inc.

A Plentiful Pairing

from Caroline Broder

Incorporating edible plant species into a garden doesn’t have to be black and white, in fact it ought to be quite colorful. Despite popular belief, there can be more to an edible garden than a simplistic linear design consisting of vegetables planted in elongated rows. The secret to a bountiful yield and a reduced grocery bill is to, quite literally, design outside the lines. schiff veggiesFrom a conceptual standpoint, an edible garden ought to be organized like any other garden populated with non-utilitarian flowers. In fact, you ought to integrate flowers with vegetables. It is important to establish a sense of place, and match its functionality with its beauty. It doesn’t take much to convince even the most novice gardener that blending flowers with edibles can result in an even more aesthetically pleasing space than initially imagined, however, there is more to this method than meets the eye.

Technically speaking, by adding flowers you not only promote production but you minimize pest damage organically as well, since some of the most beneficial insects (bees and butterflies) need pollen and nectar during some point in their life cycle to reproduce. In addition, by combining contrasting textures and camouflaging odors, undesirable critters are confused and kept at bay. Several great examples of flowers that help control pests include alyssum, marigolds, echinacea, and coreopsis.

This not so new age method of gardening is significant to those who live in an urban environment and elsewhere. Regardless of where you live, the underlying intention of anyone experimenting with growing edibles is to maximize one’s harvest by exceeding the potential of your plot. The ancient Persians and Egyptians first implemented the integration of edibles and ornamentals by planting them together in spaces conveniently located to their living quarters. It wasn’t until the Renaissance when the two types of gardens were separated as a public display of wealth. Flower beds framed homes in high profile spaces, while le potager, or vegetable garden was often hidden out of sight for its lack of showy blooms and subtle fragrances. ‘Tis no longer the season to settle on this traditional execution of planting.

Edible landscaping presents an opportunity to express yourself. After choosing your favorite plant species and taking their growing requirements into consideration, it’s up to your imagination to create a dynamic space. Herbs, such as dill, can be mixed with fine ornamental grasses within a flower bed border, while apple or fig trees can be espaliered and thoughtfully planted to accentuate a perennial border. With its distinct ruffled leaves, kale is also a noteworthy edible species to consider as it can provide structure to your design. A blended garden where flowers are growing with food results in both beauty and bounty. As the English poet and designer William Morris once said about your house, “have nothing in your house that you do not know to be useful, or believe to be beautiful,” applies just as accurately to your garden.

(References include opinions and observations from designers Erica Shaffer, Margie Grace, Ros Creasy)

Time to Plant Fruits, Nuts and Berries

The Late Winter Window:

Time to Plant Fruits, Nuts and Berries

By Brian Barth

The first warm weather of spring sets off a frenzy among gardeners. Seasoned growers, however, get going a month or so before, especially those wanting to establish perennial food plants. Why? There is a brief window after the heaviest freezes have passed, but before most deciduous plants have broken dormancy.

If the roots of a plant have to be disturbed, it’s always best to do it when they are not actively growing. When it comes to fruit and nut trees, berry bushes and perennial vegetables, there is an additional reason to plant at this time—they can be purchased without a container or soil, meaning their roots have grown unrestricted. ‘Bare root’ plants, as they are called, cost less, but more importantly, at least for fruit trees, the roots are splayed out natural—the way they grow in the ground—rather than coiled up in an artificial form. Coiled roots are one of the hidden causes of languishing fruit and nut trees; they often never fully recover.

Bare root season begins as soon as the soil can be worked in late winter or early spring. Bare root plants don’t need a massive hole; dig it just big enough to accommodate the root system. As most tree roots splay out in a conical shape, it may be necessary to create a cone of packed soil for the root system to rest on. Otherwise, they tend to sink after planting, dropping the root crown several inches below the soil level and making the tree highly susceptible to crown rot.

Another trick to the art and science of tree planting is to orient the graft union away from the sun. Almost every commercially-produced fruit tree is grafted onto a separate rootstock; the connection is the most vulnerable part of the tree.  Look for the bulge of scar tissue about 6 to 10 inches above the root crown and make sure it is pointing north to prevent sun scald.

Every type of deciduous berry, including strawberries, is available from bare root growers. The three perennial vegetables commonly grown by American gardeners—asparagus, artichoke and rhubarb—also perform better if their roots never see a pot. If planted from pots in spring or summer, they often don’t get going until the following year while their root systems get established underground.

Finding bare roots plants is not always easy, especially now that ‘big box’ retailers have become the predominant nursery outlets. Smaller, locally-owned nurseries are more likely to carry them. There are also numerous mail order nurseries that specialize in bare root edibles, though if you’re nearby, it’s best to pick up the plants in person rather than subject them to several days in the mail (Links to a few are provided below).

As soon as bare root season is over, spring planting can begin in earnest. If you take advantage of this quiet window before the seasonal rush, you will be far ahead in building an abundant landscape in the coming year.

Start a Container Garden this Spring!

By Matt Shand

A great first step towards self-sufficiency is to try growing some organic herbs and vegetables. If you’re resourceful, your residential situation should not be a hindrance on what you can accomplish, thanks to container gardening. If you can provide a container, soil, organic seed, and an occasional watering, then sunlight and mother nature will do the rest. You’ll be nomming on homegrown salsa before you know it.

Finding The Right Container

For starters, you’re going to need some containers. Depending on what you’re growing, you can get very inventive here. Herbs can be grown in drinking glasses or old coffee pots, while vegetables requiring additional space for roots can be grown in old backpacks, heavy-duty garbage bags, or my preferred method, 5 gallon plastic buckets. As a general rule, if something can hold dirt, chances are you can use it for gardening. No matter what container you end up using, it’s a good idea to poke a couple holes in the bottom so that excess water can drain out as necessary.

Craigslist is a great resource for free ‘junk’ that can be upcycled for gardening, as are moving sales and garage sales. If there are Firehouse Sub Shops in your area, they sell their used 5 gallon pickle buckets for $2, which then goes directly to their charitable non-profit for firefighters and public safety. Thrift stores might have old buckets or trashcans, and if all else fails, you can purchase new gardening containers from stores like Walmart or Home Depot.

Getting Your Hands on Dirt

If you own or rent a home, or know someone who does, all you need is a shovel (and permission!) and you should be able to fill your containers with soil in no time (although you may wish to mix in some organic fertilizer to ensure your plants receive proper nutrition). If you live in an apartment or in a city, you can purchase topsoil, potting soil, and humus (fertilizer, not the condiment) from the garden center at any warehouse store.

I Feel the Need… The Need for Seed

Cheesy subheadings aside, getting organic seed is pretty painless – once you’ve decided what you want to grow, that is. The main variables to consider are temperature and sunlight. A little internet research upfront can save you loads of trouble in the long run. Simply search for whatever you’d like to grow and the region that you live in. Googling ‘growing potatoes in Georgia’ will tell you there’s a short season to grow in the spring before it gets too hot, and a long season to grow in the milder fall and winter months. Growing indoors is a game-changer, especially for herbs, so don’t be afraid to experiment!

When you’re ready to pick up seed, keep in mind grocery stores often sell organic packet seed, and mostly all garden centers should have them on hand. There are also numerous websites from which you can order organic seed: is known for carrying a wide variety of organic heirloom varieties, and has an array of merchants as well.  Worst case scenario, you can purchase seedlings or young plants and transplant them to your own containers, though it may be difficult to find organic seedlings (not to mention half the fun of growing anything is planting the seeds and watching them sprout!)

The Power Is Yours!

With your containers filled with soil and your seed in hand, you’re ready to rock. The packets the seed came in should have instructions on how to plant the seeds, the depth and spacing, how much to water and when, and other tips on how to successfully grow healthy, productive plants. You shouldn’t run into any pest or disease issues, but if you do, the internet is invaluable for finding cheap, easy, organic solutions to common gardening problems. One of the best parts of container gardening is that your plants are fully mobile. If they’re in an area that isn’t getting enough sunlight, or if they’re getting too much sunlight, you can relocate them without too much hassle.

That’s all it takes to start your own organic container garden. In a few months, you’ll have fresh herbs on hand to experiment with in the kitchen, and loads of fresh vegetables as well! Make your own ketchup or tomato sauce, learn how to pickle cucumbers, make your own sauerkraut, or just eat everything right off the vine.

Putting the Garden to Bed

By Brian Barth

With the fall harvest fading and the holiday season around the corner, it’s a good time to wrap up the year in the garden.  Take time to note the accomplishments of the season, what worked well in the garden this year and what didn’t.  Make some mental notes about what varieties of lettuce grew the best and should be re-planted or which bed to plant the nightshades in for next year to keep a step ahead of the ever-present tomato blight.  Store the memories and ideas for improvement away until next season and pull some of nature’s warm blanket over the beds for their winter rest.

Autumn’s fallen leaves are winter’s protective ground cover and the seeds of spring fertility.  Some people labor for days raking up the leaves in their yard; wise gardeners make the rounds and pick up all those leaf bags sitting out on the curve and bring home the bounty to cover their veggie beds.  A 6-inch layer of leaves over the soil shrinks down to an inch by spring, as the organic matter decomposes into the rich, crumbly, and proverbial, ‘black gold’ of fertile soil.  In the interim, the soil is held safe from torrential rains and you can look out from your window, feeling content that everything is in its proper place so you, too, can rest.

If you find you’re not quite ready to rest, there’s one more step that will make things easier in spring.  Before laying down leaves, go ahead and loosen up the soil.  Work it with a rototiller or ply it with a digging fork, if that’s your style, just as you would in spring to prepare for planting.  Incorporate manure or composted kitchen scraps to replace some of the nutrients removed in the season’s harvest.  Dried leaves are another ingredient to add to the medley, but they should be shredded first.  If you don’t already have one, a small electric shredder for this purpose should be on your Christmas list.  There are even devices that vacuum the leaves from the ground, shred and bag them simultaneously.

Once the beds are formed to perfection, their bellies bulging from the fall feast, add the cover of leaves and allow the garden to digest.  By spring, all those nutrients will have cooked down into a fertile brew, ripe for planting.  Pull back the remaining leaves and plunk your seedlings right into the soft soil.  The leaves can stay as mulch for the next growing season, though they may need to come off temporarily to let the soil warm at planting time.

Over the coming months, we’ll take time to reflect on the garden, it’s meaning in our lives and seek direction for the next growing cycle.  Winter is time to rest, to dream and to plan.  For many, it’s a time to tinker with new designs without the pressure of timelines.  Before long, the season will force us again from our reverie and give another opportunity to put our ideas and inspirations into practice.

The Soil Is Alive: Fertility & the Biology of Decomposition


If a crumb-like soil structure sets the stage for fertility to occur and chemical reactions are the catalysts, biological organisms are the active agents that create the conditions for plants to thrive in.  Every gram of healthy garden soil contains hundreds of millions of microbes that play a critical role in the breakdown of nutrients and their assimilation by plants.  Fungi, earthworms, sow bugs and a host of other organisms consume decaying plant matter and transform it into fertilizer for plants.


An Ode to Organic Matter

Fertile soils are fostered and maintained by the organisms of the soil food web.  Some of the major players in this system and what gardeners need to know about them are discussed below.  However, the first thing to understand about the soil food web is the role of organic matter as the basic foodstuff of soil organisms and thus the foundation of soil fertility.

In essence, organic matter is the once-living remains of plants and animals.  It is composed primarily of carbon-based compounds, as well as varying degrees of nitrogen.  Most of the nitrogen content dissipates into the atmosphere as the material dries out.  However, some nitrogen also accumulates in the soil during the process of decomposition.  If the source of organic matter is dry and woody, the nitrogen content will be very low and the microbes that breakdown the organic matter will consume any nitrogen that is already in the soil to sustain themselves.  Forms of organic matter like manure, fresh grass clippings, and food scraps that are moist and non-woody have a high nitrogen content and thus add nitrogen to the soil (or compost pile) during decomposition.


Who Creates Humus?

The end product of the decomposition of organic matter is humus, a complex substance that is the basis for long term fertility.  Humus provides little in the way of nutrients directly to plants, but maintains the perfect environment for plants to have the nutrients they need at the right time and in the ideal chemical form.  The presence of humus gives rich topsoil its dark color and crumb-like texture.

Applying organic matter to the soil builds humus content, aided by a medley of micro-organisms.  Four of the major players are:

  • Fungi – responsible for much of the initial breakdown and conditioning of coarse organic matter (i.e. wood chips) so that smaller organisms can start “chewing” on it.  The mats of string-like mycelium (usually white) seen where woody matter contacts the soil is evidence of fungus at work.
  • Insects – from sow bugs to millipedes, compost piles should be full of insects chewing away at dead plant parts, aiding in the mechanical process of decomposition
  • Earthworms – these are the heroes of gardeners everywhere for the work they do in grinding up organic matter, excreting it as enriched “castings.”  Large brown earthworms live in the soil horizon, physically aerating the soil with their worm holes, while little wriggly, red worms can be found on the surface of the soil under the duff.  It is the latter group that is used in worm composting (vermiculture)
  • Bacteria – a myriad of microscopic creatures that are responsible for the chemical decomposition of the tiny bits of organic matter left by the larger decomposers.  There are numerous highly specialized species that each performs a specific function in the reconfiguration of organic molecules that results in humus formation


*For further details on the organisms responsible for decomposition and their roles in a compost pile, see


The Niceties of Nitrogen-Fixation

Many farmers and gardeners are accustomed to applying nitrogen fertilizers for the lush green growth that results.  In the previous posts, we’ve discussed the role if nitrogen in plant growth, its storage in the tissues of plants and animals, and the release of nitrogen into the soil and air during the process of decomposition.  Plants scramble to complete for available nitrogen in the soil, as it is a highly volatile substance that readily loses its soluble form and escapes into the atmosphere.  However, as you may surmise, nature has devised a process to reclaim atmospheric nitrogen and put it back in the soil where plants can use it.

There are bacteria whose job it is to take nitrogen from the air and “fix” it in a soluble form.  They don’t fly around in the sky to do it, but are able to extract nitrogen from the air that’s already mixed in with soil and water (which contains a whopping 79% nitrogen, making plants jealous).  Of most interest to farmers and gardeners are the Rhizobium bacteria that live on the roots of most leguminous plants.  Agriculturalists have essentially domesticated these microbes over the millennia, harnessing their power to increase the nitrogen content in their soils.

If you pull up the roots of a legume – peas, peanuts, clover, beans, etc. – you are likely to see little white or pink nodules on some of the roots.  They look like a tumorous growth, but are actually the factories where nitrogen-fixation takes place.  Rhizobium bacteria have a symbiotic relationship with their host plants – they receive energy and nutrients from the plant and supply nitrogen in return.  The more pinkish in color the nodules are, the greater the quantity of nitrogen transfer. These plants exhibit luxuriant growth and when they die, the remaining nitrogen stored in the nodules is delivered to the soil for other plants to use.

A thorough overview of the nitrogen fixation and its relevance too agriculture can be found here

In the coming weeks, we will share ideas and techniques to improve soil quality so your garden grows more bountiful with less effort – including the use of nitrogen-fixing crops and Rhizobium inoculant to introduce the bacteria to the soil.


Written by Brian Barth

A Time to Plant, A Time to Grow


In the Deep South and other mild winter regions of the country, spring has been in full fling for a couple of months now.  Meanwhile, places like Madison, Wisconsin and Denver, Colorado are just starting to wake up to warm weather.  Wherever you are gardening, it’s critical to understand the right time to plant individual crops ensure a successful harvest.  A good grasp of the effects of temperature on different types of plants is integral to this understanding.

When it comes to annual vegetables, they can generally be divided between warm season and cool season crops.  (See below for a complete list of warm and cool season crops according to their plant families).  Warm season crops require frost-free weather to survive, and they generally need warm nights and long, hot days to thrive and produce well.  On the other hand, cool season crops tolerate frosts and have evolved to do most of their growing in the mild weather of fall and spring.  When the hot weather hits in early summer, most of these will attempt to set seed, signifying the end of their life cycle.   If they are planted as fall crops, they will grow until the first hard freeze, though many species will survive mild winters and begin to grow again in early spring.

To know when to plant your warm season vegetables, it is helpful to know the average date of the last frost in spring and the first frost in fall (see the link below for a reference).  It is a good idea to add a few weeks to the average date of last frost before planting heat-lovers like tomatoes, melons, and okra because they will not begin to grow until nighttime temperatures are consistently above 50 degrees.  Another important piece of information is the time to maturity, which is usually listed on seed packets.  This is just an estimate, which depends on the actual weather, soil conditions, pest problems, and other factors.  Subtract the days to maturity from the average date of first frost to determine the latest date to plant a warm season crop.  It is wise to subtract several more weeks to account for the unknown variables mentioned above and because the growth of warm season plants slows down with the shorter days and cooler nights at the end of the growing season.

The time to plant cool season crops in late winter or early spring is dependent on temperature and the ability to work the soil.  A good rule of thumb is to plant one month before the average date of last frost.  Earlier planting may be possible as long as the ground is not frozen or snow-covered.  Heavy clay soils are likely to be very wet at this time of year, which will delay planting time until they have dried sufficiently to be tilled.

Cool season crops for fall are actually planted in late summer.  Ironically, cool season crops do most of their growing during the warmest parts of the cool season, and are then ready to harvest when the nippy weather first hits.  Again, the actual dates of planting depend on how early winter comes.  A good rule of thumb is to plant fall crops about two months before the average date of first frost.  Later plantings of certain crops, mainly greens, can succeed in mild winter areas because they will overwinter and come into maturity the following spring.  In cold climates with really short growing seasons, cool weather crops get planted at the same time as warm weather crops and will grow throughout the summer, setting their seed in fall.

Timing is everything in the world of plants.  The difference between cool season and warm season annuals is determined largely by day length.  Cool season crops have evolved to set seed when day length is approaching its peak at the summer solstice.  Warm season crops are programmed to set seed as the days are becoming shorter in fall.  The dynamic pulse of the seasons gives a rhythm to a gardener’s life that is punctuated with the wonderful busyness of planting times and lulled by the long interludes of tending to the crops as they grow.  It is important to recognize this rhythm and pace and let its wise cadence be our guide.

The easiest way to learn the difference is to study them according to the common plant families to which most annual vegetables belong.

Solanaceae – known as the nightshade family, includes many popular warm season crops, such as tomatoes, peppers, eggplant, and potatoes.

Leguminosae – the bean family is split between warm and cool season vegetables.  All types of green beans (including there yellow and purple cousins) and field peas (everything from lima beans to black-eyed peas) are warm season crops, while fava beans and all types of sweet peas (snow peas, English peas, sugar snap peas) produce best in cool weather.  Peanuts are also warm season legumes.

Curcurbitaceae – the squash family is full of heat-lovers, like cucumbers, melons, zucchini, pumpkins, and of course squashes.

Brassicaceae – this includes a long list of cool season crops, like broccoli, kale, collards, mustard, Brussels sprouts, cabbages, cauliflower, radishes, turnips, and rutabagas, plus tatsoi, bok choi, and most other Asian greens.

Chenopodiaceae – spinach, beets, and Swiss chard are all cool season vegetables in the goosefoot family

Asteraceae – the aster family includes many cool season crops, including all lettuces, chicory, endive, and artichokes

Apiaceae – carrots, celery, dill, cilantro, parsley, and parsnip are all cool season vegetables

Alliaceae – cool season vegetables including garlic, onions, shallots, chives, and leeks.

Miscellaneous – corn is a warm season crop in the Poaceae (grass) family; okra is a warm season crop in the Malvaceae (mallow) family; basil is an annual warm season herb in the Lamiaceae (mint) family.

*A list of average first and last frost dates for select American cities can be found at:


For a more detailed list, see:


Written by Brian Barth

The Chemistry of Plants and Soil

How do soils develop a good tilth structure and why does it allow plant life to flourish? The answer has a lot to do with chemical bonds that occur at a molecular level. Soil particles, water molecules, mineral compounds, biological enzymes, and microbial organisms interact in a complex web of relationships that make plant life flourish.

It is not the sheer presence of nutrients in the soil that causes plants to grow, it is their precise chemical composition and degree of solubility. In a fertile loam soil, minerals are broken down in chemical reactions to become water soluble and available for plants to absorb. There are chemical bonds that attach water molecules and nutrients to particles of soil, as well, preventing the nutrients from leaching away.

Without delving fully into the science of soil chemistry, there are some basic points that are relevant to all gardeners – soil pH, the purpose of the essential macro- and micro-nutrients, and the carbon to nitrogen ratio.

Soil pH

Soil pH is the measure of its relative acidity or alkalinity, expressed on a scale from 1 to 14. Above 7 is considered alkaline; below 7 is acidic. There are many natural factors that affect the pH of soil but, in general, areas of high rainfall have more acidic soil and arid areas tend to have alkaline soils. A slightly acidic pH (between 6 and 7) is ideal for the widest range of plants. Other than desert species, few plants tolerate highly alkaline soils. However, quite a few species require acidic soil, including blueberries and many ornamental species – hydrangeas, rhododendrons, azaleas, gardenias, and camellias are notable examples.

In general, soil pH governs the uptake of specific nutrients by plants. Over time, the management of garden soils can either increase or decrease pH. This can be a good thing (and done intentionally) in cases where soils are excessively acidic or alkaline. Or, it can be the unintended consequence of poor practices and lead to the decline of fertility – see the best management practices below for some good ideas and some things to avoid. For a reference on testing soil pH and how to use soil amendments to increase or decrease pH as necessary, see:


Nitrogen, phosphorus, and potassium are the essential nutrients that plants require in large quantities for their growth and maintenance. Iron, boron, manganese, copper, chlorine, molybdenum, zinc, are some of the nutrients that plants use in very small quantities, but they are equally essential to the health of plants. In fertilizers, nitrogen, phosphorus, and potassium are represented by the letters N, P, and K, respectively. The three numbers that appear on bags of fertilizer represent the percentage of each found in the fertilizer. Nitrogen is responsible for the green, vegetative growth of plants. Phosphorus has many roles in the physiology of plants, but gardeners apply sources of phosphorus to strengthen the flowering and fruiting cycle of plant life, as opposed to the vegetative stage stimulated by nitrogen. Potassium strengthens the root systems of plants and plays an important role in disease resistance. In reality, the transfer of nutrients from soil to plants is highly complex and is determined by a host of environmental factors such as pH, temperature, moisture level, and others.

Carbon to Nitrogen Ratio

An understanding of the ratio of carbon to nitrogen (C: N) in soils is critical knowledge for gardeners. Carbon forms the bulk of plant tissues and is largely what is left when a plant dies and decomposes. Nitrogen is found to a lesser extent in the tissues of plants and dissipates into the atmosphere quickly after a plant dies. There is a fundamental relationship between the two elements that needs to be balanced for sufficient nitrogen to be available in soils. The reason is that nitrogen is consumed by the microbes responsible for the breakdown of carbon-based compounds. Thus, nitrogen will become deficient when excessive sources of carbon are introduced to the soil. The optimum C:N ratio in compost piles is approximately 30:1. Animal manures have a very low C:N ratio, while dried leaves, newspaper, and sawdust have a very high ratio. These materials are often mixed to establish an optimum ratio in a compost pile. For a complete list of the C:N ratio of common garden materials, see:

Next week, we will continue the discussion of soils with a brief introduction to the living organisms of the soil food web, and the basic biological processes that can be cultivated by gardeners to achieve highly fertile soils.

Urban Agriculture

Organic Gardening Fundamentals:

Soil Ecology and Plant Life

Part 1

By Brian Barth

 Real farmers don’t grow crops, they grow healthy soil….

This is an old adage that beginning gardeners eventually learn, and seasoned gardeners continue to develop their understanding of. Over the next few weeks, I will outline the ABC’s of soil science—including the structure, chemistry and biology of soil fertility—and give an overview of the best soil-building practices for home gardeners. Each week’s posting will build on the information from the previous week and together should illuminate some of the fundamental relationships between soil life and the growth and good health of your vegetables, herbs, fruits, berries, and other crops.


Next time you have the opportunity to be in the forest, find your way to a tree that is at least two feet in diameter. Kneel down and pull back the layer of duff with your hands to see the soil that nature has created in the time since the landscape was last disturbed. Scoop up a handful and you will know first-hand the holy grail of organic gardening—the fertile loam.

The cookie crumb texture, dark color, and earthy smell of the soil in a mature forest are the end results of a natural process that can be mimicked and accelerated in a garden environment. Farmers use the word tilth to describe the water- and nutrient-holding capacity of fertile soils with a loose, crumbly texture. If you used a microscope to examine the structure of a soil with good tilth, you would see something like the texture of a sponge—an immense labyrinth of cracks, crevices, and crannies where water molecules (and the nutrients they carry) can seep in and be stored. The immense surface area of each particle of a loam soil is easily penetrated by tiny rootlets, the active tips of a root system that seek out and absorb moisture and nutrients.

To unravel the mysteries of fertile soil and the processes that create it, we must begin with understanding the three physical components of soils and their properties. Sand, silt and clay particles each add different qualities to soil based on their relative concentration:

  • Sands are the largest soil particles and are essentially tiny pieces of weathered rock. Sandy soils have a lot of air space, which allows moisture to dissipate quickly, leaching away nutrients in the process. Thus, extremely sandy soils have a low concentration of nutrients, but offer excellent drainage for the plants that need it.
  • Silt particles are medium-sized and have moderate of nutrient- and moisture-holding ability. Silt results from the weathering of sand particles and is often deposited in large quantities in flat, low-lying areas by the natural process of erosion. The world’s great river valleys are agricultural powerhouses because of the high silt content of their soils.
  • Clays are the tiniest soil particles and are formed by a chemical process rather than weathering. They are flat, plate-like particles held together by chemical bonds. Clay particles attract and bond with water and nutrient molecules,  providing a slow and steady release to plants. However, the dense nature of soils with a high clay content can impede drainage, limiting the growth of some plants.

A perfectly balanced loam has a 40-40-20 ratio between sand, silt, and clay, respectively. Knowing the relative concentration of the three particles in your soil is important for choosing the best strategies to boost fertility. Fortunately, this information is easy to come by:

  1. Fill a glass jar with approximately 50% soil and 25% water.
  2. Put the lid on and shake for at least thirty seconds.
  3. Place the jar on a table and observe what happens.

Sand particles fall immediately to the bottom. The silt particles will settle on top of the sand within about 30-60 seconds. The clay is the last to settle and can actually stay suspended in the water for 24-48 hours. Once the water is perfectly clear, there will be three distinct layers that show the proportions of the different size particles.

Next week, we will dive into the chemical reactions in garden soil that transform mineral compounds into naturally-occurring fertilizers and learn the properties of the most important plant nutrients.

Spring on an Urban Farm


Spring on an Urban Farm

By Brian Barth


On rooftops and in backyards, in city parks and vacant lots, in ghettoes and suburban neighborhoods across North America and the world, a new rationale of urban land use has taken root.  The oldest of reasons for land development is returning in the most modern context.  Agricultural productivity is slowly but surely becoming a measure of urban progress.  The movement of urban farming is buzzing like a garden in Spring.


In many cities, it is increasingly difficult to find a neighborhood that doesn’t have some sort of community garden.  In Washington, DC one family is setting the trend in their neighborhood and beyond.  At 1600 Pennsylvania Avenue, the Obamas are leading the country towards greater food sovereignty in a strange way for capitol hill – by example.


In Spring of 2009, Michelle Obama and friends broke ground on an 1100 square foot vegetable garden because she wanted her family to have access to fresh produce, as well as the experience of producing it.  The existing lawn was tilled in.  Rows were delineated and a planting scheme carefully laid out to insure there would always be something in season.  Bees were brought in to pollinate the crops and a nearby apple tree bore fruit for the first time 25 years, thanks to their diligent work in pursuit of nectar.  The Obama family and their guests now dine from the garden on a daily basis and, five years later, the movement of urban food production is sweeping the country like wildfire.


When City of Atlanta Mayor Kasim Reed announced plans to build an urban farm center directly across the street from his office in downtown Atlanta in 2011, he joined the ranks of urban leaders across the country who have been swept up in the feeling that food production will have an important role to play in the healing and future prosperity of our cities.  “We are very excited about the opportunity to create a sustainable and accessible greenspace in the heart of downtown,” Mayor Reed proclaimed during a press conference to announce the project.   Atlanta has well over 300 community gardens in its metro area and new market farms are cropping up within city limits every spring.


The concept of using existing green space for food production is a win-win for residents, city planners, developers, and urban ecosystems.  As much as our urban landscapes are paved over and built on, they still contain lots of little green splotches, like backyards and street trees – and some big ones, like city parks and golf courses – that have both intrinsic and economic value.  If some of these, where appropriate, are transformed into food-producing landscapes, that value will only be increased.  With the addition food production, these landscapes can continue to provide recreation opportunities, give refuge to wildlife, and create the beautiful views that drive up property values.  Yet, they will also contribute two other valuable amenities to our lives: access to fresh food and participating in the experience of growing it.


Urban agriculture may not yet be a mandate at the national level, but it may not be long given the sentiment of the First Lady, the leaders of many of our largest urban centers, and a growing tide of citizens everywhere.  It is Spring once again, and the old-fashioned art of agriculture has emerged from the cracks in the pavement of our modern metropolis.


The easiest way to learn the difference is to study them according to the common plant families to which most annual vegetables belong.


Solanaceae – known as the nightshade family, includes many popular warm season crops, such as tomatoes, peppers, eggplant, and potatoes.   


Leguminosae – the bean family is split between warm and cool season vegetables.  All types of green beans (including there yellow and purple cousins) and field peas (everything from lima beans to black-eyed peas) are warm season crops, while fava beans and all types of sweet peas (snow peas, English peas, sugar snap peas) produce best in cool weather.  Peanuts are also warm season legumes.


Curcurbitaceae – the squash family is full of heat-lovers, like cucumbers, melons, zucchini, pumpkins, and of course squashes.


Brassicaceae – this includes a long list of cool season crops, like broccoli, kale, collards, mustard, Brussels sprouts, cabbages, cauliflower, radishes, turnips, and rutabagas, plus tatsoi, bok choi, and most other Asian greens.


Chenopodiaceae – spinach, beets, and Swiss chard are all cool season vegetables in the goosefoot family


Asteraceae – the aster family includes many cool season crops, including all lettuces, chicory, endive, and artichokes


Apiaceae – carrots, celery, dill, cilantro, parsley, and parsnip are all cool season vegetables


Alliaceae – cool season vegetables including garlic, onions, shallots, chives, and leeks.


Miscellaneous – corn is a warm season crop in the Poaceae (grass) family; okra is a warm season crop in the Malvaceae (mallow) family; basil is an annual warm season herb in the Lamiaceae (mint) family.


*A list of average first and last frost dates for select American cities can be found at: 


For a more detailed list, see:


Brian Barth
UAI Co-Founder