Soil quality is a major contributor to plant (and planet!) health and resilience. Many aspects of a soil contribute to its overall condition, including
- organic matter and humus contents
- aggregation and porosity
- mineral content
Wonderfully, one of the best methods for improving soil quality is using it to grow crops that enhance one or more of these attributes.
Cover crops and green manures are popular methods of introducing soil-enhancing plants into your production system. They can be grown during the winter, in summer between cash crops, or be in place for a full year.
These soil-improving crops offer many and diverse benefits. They can lead to increased soil fertility and water-holding capacity. They can prevent and correct soil erosion and compaction while generally improving texture. And they can be used to absorb excess nutrients (from compost or manure applications, for example) and thus prevent nutrient leaching.
Depending on crop choice and management, they can also result in decreased weed pressures and increased beneficial insect populations.
Improving soil fertility is a specialty of many soil-improving crops, which they achieve in different ways. Legumes fix nitrogen. Some plants produce large quantities of biomass (above and below ground) to add to the soil’s organic matter. Still others mine minerals from the subsoil, making them available in the topsoil.
Many plants transport some of their photosynthetically-produced sugars through their roots and release them to the soil. These act as biological stimulants to the microbial soil community (including mycorrhizal fungi), providing energy for its growth and vitality. In turn, this increases soil water-holding capacity and mineral availability in the soil to the betterment of the plant community.
This can be particularly effective when the soil-improving crops are from plant families typically underrepresented on farms and in gardens. They’ll enhance ecosystem biodiversity at the same time.
The following plants offer a diversity of soil-boosting benefits. Pay attention to their unique attributes and think about how they may work together—whether simultaneously or successionally!
A familiar green manure that prefers loose, moist (not soggy) soil, buckwheat (Fagopyrum esculentum) is for spring planting and known as an excellent soil conditioner.
Its rapid establishment and tight canopy allow it to shade out and suppress weeds, another of its finest attributes.
An annual and member of the infrequently seen Rhubarb family, buckwheat produces plant root exudates which will improve the soil’s biological diversity. Additionally, they enhance phosphorus availability in the soil.
Read more: Grow buckwheat for the bees!
Favored for erosion control and weed suppression, cowpea (Vigna unguiculata) can reach 3 feet in height. A nitrogen-fixing legume, it also improves soil fertility.
Exceptionally heat and drought tolerant, this annual was made to withstand the harshest of summers. And due to its tolerance of partial-shade conditions, it can be used as a living mulch.
Egyptian or Berseem Clover
An annual with a high rate of nitrogen fixation, Egyptian clover (Trifolium alexandrinum) has a tolerance of a range of soil types (excluding sand) and environmental temperatures. It can also withstand drought conditions, excess soil moisture and excess salinity—though it will positively thrive in slight alkalinity.
In good conditions, this high-quality forage produces enormous biomass. This clover’s rapid growth makes it ideal in various situations, all of which benefit from its ability to suppress weeds.
This perennial and member of the sunflower family possesses the familial characteristic of a substantial taproot. Its root system helps it to be drought tolerant, an improver of soil texture, and a miner of minerals.
Forage chicory (Cichorium intybus) favors well to moderately drained soils with medium to high fertility that are in full sun. It’s a favorite of cattle and an excellent addition to a diverse animal diet. And it is, of course, less prone to flowering than its familiar roadside-dwelling relative.
Attractive to the eye and numerous insects, though due to the itchy pubescence covering it all animals prefer to admire it from a distance, lacy phacelia (Phacelia tanacetifolia) brings balance to soil nutrient levels. More specifically, it’s a nitrogen scavenger. This means it gathers and holds nitrogen in the soil, preventing any run-off and retaining it for use by future crops.
A rapidly growing annual, it suppresses weeds by outcompeting them for water and nutrients. This member of the borage family has a reputation of being a soil-improver that conditions the topsoil better than any other plant.
Thanks to the large, deeply growing roots of these radishes, Korean Radish, or Asian Daikon Radish, (Raphanus sativus var. longipinnatus) greatly improve soil tilth by breaking up compaction and plow pans. You might want to pull a few for food or animal fodder as well.
Whether planted in spring or in the fall to overwinter, this annual (which is a biennial flowerer) is known as a biofumigant of the soil, producing root exudates that can eliminate root-knot nematodes. The presence of these soil pests can be detrimental to the growth of many plants and is absolutely disastrous to root crop production.
This annual produces a dense mass of roots that reach far down into the soil, leaving a loosened soil texture as they decompose. Oats (Avena sativa) can be planted early and grown in summer or planted later in the season. They’re cold-hardy enough to continue growth as cool weather moves in but sensitive enough that it will winterkill (see “A Management Position,” below) and become an automatic mulch for the following spring.
A forage-able grass crop and nitrogen scavenger, oats are also known to produce substances that have an allelopathic or chemically inhibiting effect on seed germination, which functions well in weed suppression.
This legume is easy to grow provided you offer it a cleanly prepared seed bed. It fails to compete with perennial plants. Growing very well in the summer heat and in average-to-dry soils, partridge pea (Chamaecrista fasciculata) will typically reach 2 feet in height.
A nitrogen fixer (naturally), farmers frequently use it in areas where erosion control is critical. It holds the soil, and its attractive appearance adds beauty valued by humans. Furthermore, in addition to lovely flowers, this plant has extra-floral (nonflower) nectaries and so appeals to many pollinators and other beneficial insects.
Read more: Grow pea shoots for delicious greens.
Rye (Secale cereale) is exceptional in many respects. Its root production is substantial, producing below-ground biomass reaching into the subsoils. It, too, is a grass with nitrogen scavenging and (strongly) allelopathic traits and is also an inhibitor of root-knot nematodes.
Often considered the hardiest soil-improving crop, rye can be planted in downright chilly soil and therefore has its window for planting open quite late (an advantage when dealing with crops harvested late in the year).
A winter annual, it resumes its growth in the spring. Also, its shade tolerance leads to greater opportunities to combine its growth with other plants, whether simultaneously or successionally.
Yellow sweetclover (Melilotus officinalis) and white sweetclover (Melilotus alba) are both monumental nitrogen fixers, aboveground biomass producers (potentially reaching 6 feet), nutrient miners and soil compaction rectifiers, all of which is aided by their deep, aggressive taproots.
Though yellow sweetclover (a biennial) has better drought tolerance, heat tolerance and biomass production, white sweetclover (an annual) is taller and “stemmier” and sometimes considered a better soil tilther. These willing self-seeders are ideally planted early during the cool, damp spring months for better establishment.
A Management Position
Soil-improving crops can be implemented on a large (as in plot or field) or small (as in row or bed) scale. It’s just a question of managing them properly based on the situation. But first, there are decisions to be made with your soil-improving crops.
Are they to be spring, summer or fall planted, and what will they be? Are you prepared to monitor soil-improving crops for diseases or insect outbreaks that may affect neighboring or future cash crops with the same susceptibilities (as can happen with radish or mustard soil-improvers)?
Do you wish to plant a mixture of species to produce a greater effect? For example, when planted together, a legume will fix nitrogen from the atmosphere while a grass will retain it in the soil.
Or a rapidly growing crop will “nurse” a slower one, producing conditions that allow both to become established. (Often this is an annual crop nursing a perennial, though, by way of example, oats nursing Egyptian clover is an annual nursing an annual.)
When it’s time to end your crop, will you do this with mowing, harvesting or grazing and then tillage; rolling/crimping, hand hoeing or manual pulling; or leave it to be winterkilled by cold weather?
Some of the managing you must do is simply timing steps properly. For example, there is terminating your crop before it develops tough stalks that resist decomposition (an issue with rye). And cutting a flowering soil-improvement crop prior to its seed set so that it does not reseed itself in a weedy fashion (sweetclover, hairy vetch and radish, to name a few, are known for this).
Coordinating between cash crops and soil-improving crops must be appropriately timed also. Crop decomposition uses moisture (making it unavailable for the growth of new plants), and its nutrients need time to be released as well.
Further, the allelopathic effects of some soil improvers on seed germination can influence subsequent crops as well as weeds. The effect is temporary and sometimes only on small-seeded crops. Generally, a 2-to-3-week window between improving-crop removal and the planting of your cash crop will avoid any resource competition or unfavorable influences.
And what other uses will you find for your soil-improving crops? Those which produce sufficient biomass may be repeatedly cut as a mulch source prior to flowering [most plants that have reached their reproductive (flowering) stage will not re-grow after being cut]. Others palatable to animals (whether cattle, goats, pigs or chickens) can be used as a food source for them, through grazing or mowing/harvesting.
Moreover, crops allowed to flower will offer food sources and other advantages to beneficial insects, including pollinators. Finally, you should note that traditional flowering plants (e.g., cornflowers, cosmos, dwarf sunflowers) can also be included in a planting to provide beauty, benefit insect populations and enhance diversity while performing soil-improving benefits of their own.
Whether your agrarian aims are personal or professional, or the extent of the soil you steward great or small, it and your plants will respond positively to the use of soil-improving crops.
Different Strokes for Different Folks
Soil-improving crops will produce a favorable effect when planted in many different situations. Sometimes soil improvement and/or protection is the objective of a planting. Sometimes improving the soil isn’t the primary goal, but it helps to better fulfill the principle purpose as healthy plants in healthy soil will always be more effective at their job.
Many soil-improving crops—such as clovers, vetches, grasses, buckwheat, selfheal, sunflowers, rudbeckias and salvias—can be used in most or all of the plantings below.
A buffer strip is land maintained in permanent vegetation in order to help achieve and maintain good air, soil and/or water quality.
It may slow surface runoff, control wind erosion, stabilize a stream bank, provide a space of protection from pesticide drift or perform some other environmental service.
A filter strip might be thought of as a particular kind of buffer strip. They are in place to reduce the concentrations of (leaching) nitrogen and phosphorus, sediment and pesticides from agricultural land into surface water specifically.
A cover crop is grown in between cash crops (in the temporal sense) when a cash crop wouldn’t normally be growing. In many places, this means growing in winter and with crops that are winter annuals or perennials (perhaps short-lived ones).
Though cover crops and green manures (directly below) offer essentially identical benefits, erosion prevention is often considered of particular importance with cover cropping as it protects soil that might otherwise be left bare during an unproductive season.
Green manures are grown in place of a cash crop, i.e., grown during the main growing season. Because production time is being “sacrificed” with green manures, cover cropping is the more prevalent of the two practices.
However, it can be possible to grow a green manure and a cash crop in one season if you were to select a very short-season cash crop (leaf lettuce or other cutting greens, radishes, etc.) or a very short-season green manure, such as buckwheat.
In place during the main growing season—like a green manure—but not taking the place of a cash crop, a living mulch grows underneath the canopy of a cash crop where it has been interplanted or undersown (a cover crop that is grown in between cash crops spatially instead of temporally).
As well as the soil-improving benefits it yields, it lives up to its name and provides the additional benefits of mulching, including soil temperature regulation and moisture retention due to a protected soil surface.
Insectary strips can be permanent, incorporating trees and shrubs and involving rigorous maintenance. The temporary or annual insectary strip is more likely to include plants common to these plantings and will also create improved soil conditions for crop planting, as they are located on land that may be put into production.
But the main function of insectary strips is to support beneficial insects with food sources and housing/nesting materials. These are possible benefits of the other planting practices, depending on the plant varieties and maintenance methods used.
Beetle Bank or Beetle Berm
A beetle bank is, again, a planting primarily for the support of beneficial insects, but particularly predaceous ground beetles.
It fosters them as part of an integrated pest management system, intended to reduce reliance on insecticides.
A beetle bank is a raised bed or berm located within or around cash crop areas and planted with an emphasis on native grasses and flowers.
This article originally appeared in the September/October 2022 issue of Hobby Farms magazine.