Cultivating and maintaining healthy soil is crucial to the success of your vegetable garden, as it determines the health of your plants and ultimately your own health.
Healthy vegetable garden soil will provide everything your plants need to produce tasty, nutritious crops. Healthy soils will require less water, and will retain more nutrients, thereby reducing the amount of fertilizer needed.
To determine the health of your soil, use a combination of techniques. The texture of the soil, the color, and the smell are all excellent indicators of soil health. To test the soil yourself, squeeze it between your fingers and gauge how it feels in your hands. Loose and crumbly soil is great for veggies.
The color of the soil is also important. Dark brown or black soils indicate high levels of organic matter and good water retention, as well as solar heat gain. Healthy soils should smell of earth -- fresh and pleasant -- or have little odor at all. If the soil smells rotten, swampy, or like ammonia, it's a good indication of poor drainage and lack of oxygen.
Drainage can be tested very simply by digging a hole and filling it with water. If the water drains away quickly (within minutes to two hours), it is well-drained soil. If the water drains slowly (between two and eight hours), it is moderately drained. If the water is still not drained away after eight hours, the soil is poorly drained.
A great example of a biologically rich soil, the layer of soil just below the leaf litter is high in organic matter/humus; supports a diversity of biology, including earthworms; and has good water and nutrient retention. The soil is dark in color with a loose and crumbly texture.
This soil is very well drained, contains little in the way of organic matter/humus, and has little water or nutrient retention. It feels gritty to the touch, does not form clumps or aggregates, and is usually light in color.
Clay is very dense soil, which easily forms clods or "sausages" between the fingers. It has the potential to hold large amounts of nutrients and water but is often poorly drained and becomes anaerobic.
This is an ideal soil for vegetables, with nearly equal parts sand, silt, and clay. It drains well, is dark in color, and feels loose and workable in your hands. It easily forms larger aggregates and has a good amount of organic matter/humus.
This is a manufactured soil that has good water retention and structure, so it will drain well but still hold moisture. It includes peat moss, vermiculite, and perlite for structure and retention, but in a long-term sense, it doesn't contain large amounts of nutrients. For container and window-box vegetable growers, a one-to-one mixture of compost and potting soil will yield great results.
The Ball Jar Test
The Ball jar test is based on a basic principle of soil science. Soil is composed of three different particles -- sand being the largest and heaviest, followed by silt and then clay, which is the smallest and most lightweight.
By mixing a soil sample in a column of water, you can separate these particles into layers. The sand settles first since it is heaviest, followed by silt and then the clay after a day or two. The ratio of sand to silt to clay determines what textural class your soil falls into.
To get a rough idea, simply measure how much soil you began with, using a ruler and then after everything has settled, measure the amounts of each layer. Each layer as a percentage of the whole will give you an estimate of how much sand, silt, or clay is present in your soil.
Testing pH and Nutrient Levels
For the most accurate soil tests, send a sample to your local county cooperative extension service (usually affiliated with a land-grant college or university). They will test for pH, a measure of the soil's acidity or alkalinity, as well as provide a nutrient analysis for the soil. Vegetables prefer a pH that's close to neutral -- knowing your pH value will help you make appropriate choices for amendments.
Simply send a small, dry soil sample -- roughly the amount that fits onto a trowel -- to the county cooperative extension service lab along with info about what you're growing, and you can expect results within a few days to a few weeks.
Compost is very high in organic matter/humus, full of biology -- including beneficial bacteria, fungi, and nematodes -- and has great water and nutrient-retentive properties. Good compost contains on average a two-to-one mixture of "brown" ingredients (wood chips, sawdust, newspaper, brown leaves) and "green" ingredients (grass clippings). The compost will heat up as the ingredients decompose and will need to be turned periodically to introduce oxygen to the microbes. Compost is mature when you can no longer readily recognize what you started with. It should also smell earthy and pleasant, not swampy or rotten. If it smells bad, turn the pile to introduce more air. If it gets too hot, turn the pile to cool it and introduce more air. Vegetables love compost.
This soil amendment is great for vegetable growers as well. It consists of composted animal manures (usually from farm animals) and possesses all of the qualities of good compost: high levels of organic matter, good nutrient and water-holding potential, dark color, and no offensive smells.
Earthworms are beneficial for a number of reasons. As they tunnel through the soil, they create air pockets and space behind them, introducing better air and water movement into the soil. As they chew through leaf litter, their excrement (known as vermicompost) consists of round aggregates of soil particles held together by slime produced by bacteria in the worm's stomach. These round aggregates of soil are packed with organic matter and nutrients, all of which are immediately available for plants to use.
Green sand is a very useful soil amendment. Mined from marine deposits, it gets its color and name from its high amounts of potash (a source of potassium). It also helps loosen clay soils, and aids in water and nutrient retention. Green sand contains many trace elements as well. It works as a slow release, so a little bit goes a long way.
There are many benefits of mulching. Mulch insulates the soil, protecting the plants from extreme temperatures. It prevents soil from eroding away with storm water or wind and conserves precious soil moisture that otherwise would evaporate. Types of mulch include pine-bark mini nuggets, pine soil conditioner, pine needles, straw or hay, shredded cedar mulch, wood chips, composted leaves, and buckwheat hulls.
Special thanks to Uli Lorimer, curator of the Brooklyn Botanic Garden's Native Flora Garden, for sharing this information and giving tickets to the Brooklyn Botanic Garden to our studio audience. To learn more about the soil in your area, visit websoilsurvey.nrcs.usda.gov. For more information on nurturing healthy soil, check out the Brooklyn Botanic Garden's book, "Healthy Soil for Sustainable Gardens." For more valuable gardening information, check out our vegetable garden center.