Garlic Cover Crops
Growing cover crops is a common soil management practice for many garlic growers. Cover crops are an important part of any soil maintenance system, especially on lighter soils that have lower organic matter. It is important to know the goal when planting a cover crop and to select the best one for that job.
Choosing a Cover Crop
If you examine a cover crop seed supplier list you will see that there is a wide variety of cover crops available; some exotic, some more common. Each cover crop has its own attributes, some are better suited for particular uses than others.
When using cover crops in your garlic rotation, consider the following when making your selection:There are often several cover crop options for any one goal or function. Consider your specific needs and management style to select the best cover crop for your garlic growing system.
Cover Crop Function
Best Choices for Cover Crops
Legumes - red clover, peas, vetch
Fall uptake - oilseed radish and other brassicas, oat
Winter/spring uptake - rye, winter wheat
Fast growing/shading plants - oilseed radish and other brassicas, winter rye, buckwheat
Soil structure building
Grasses - oat, barley, rye, wheat, triticale, ryegrass or fibrous root systems such as red clover
Strong tap roots that grow over time - alfalfa, sweet clover
Biomass return to soil
Fall seeded - oat, oilseed radish
Summer-seeded - millets, sorghum, sudangrass, sorghum sudan
Winter rye, winter wheat, ryegrass (well-established), spring cereals seeded early
Cutlass mustard, sudans/sorghums (Sordan 79, Trudan 8,) pearl millet (CFPM 101), marigold (Crackerjack, Creole), oilseed radish (Adagio, Colonel)
Characteristics of Cover Crops
The following is information on the most commonly used cover crops.
Grasses have fine, fibrous root systems that are well suited to holding soil in place and improving soil structure. Suitable grass species for cover crops are fast growing and relatively easy to kill, either chemically, mechanically or by winter weather. Grasses do not fix any nitrogen out of the atmosphere but can accumulate large quantities from the soil.
Grasses are often referred to as either bunch grass or a spreading grass. Bunch grasses generally do not have rhizomes or stolons, just a simple root system supporting the plant. The species with rhizomes or stolons have the ability to send up new shoots from nodes on these structures, allowing the grass to spread and form a sod.
Spring cereals are well suited for late-summer and early-fall plantings. Under good growing conditions, spring cereals will produce the greatest amount of crop biomass, making them valuable for feed or ground cover. Once well established, spring cereals are relatively tolerant of frost.
Planting spring cereals in fall is not recommended because of establishment end growth.
Winter cereals are highly versatile cover crops. They can be planted in summer and will tiller and thicken due to their need for vernalization (cold exposure) before reproduction, or they can be planted in fall for soil cover. Winter cereals will generally over-winter well, providing winter and spring erosion protection. These grasses can be used to create spring wind barriers, residue mulch or killed early to minimize residue cover at planting.
Warm-season grasses such as sorghum and millet are best suited for planting into the warmer soils of late June, July and early August. They are very sensitive to frost. Root growth is extensive and the top growth lush. Be prepared to mow these grasses to keep stalks tender and prevent heading out. Do not mow closer than 15 cm (6 in.) to ensure regrowth. Some nitrogen may have to be applied to achieve optimal growth.
Legume Broadleaf Crops
Legume cover crops can fix nitrogen from the air, supplying nitrogen to the succeeding crop. Legumes will take up residual soil nitrogen or nitrogen from manure applications. They are approximately 80% as effective as non-legumes in nitrogen uptake from soil. Legumes also protect the soil from erosion and add organic matter. The amount of nitrogen fixed varies between species, although generally, more top growth equals more nitrogen fixed. Some legume species such as alfalfa and sweet clover have aggressive tap roots that can break up subsoil compaction, but this requires more than one year's growth.
Non-Legume Broadleaf Crops
These broadleaf crops cannot fix nitrogen out of the air but may absorb large quantities from the soil. Most of these crops are not winter-hardy, so additional control measures are not normally required. They should not be allowed to go to seed, as the volunteer seed can become a significant weed problem.