As winter approaches and you harvest the last of summer’s vegetables from your garden, sowing Austrian winter peas is an ideal way to protect your precious garden soil through the winter while providing green manure in the spring. And, as a bonus, the leafy green vines may be periodically pruned and fed to chickens and other livestock at a time when fresh forage is otherwise scarce.
What is a Cover Crop vs. Green Manure?
Cover crops and green manures are plants grown for the benefits they provide the soil. A cover crop suppresses weeds and protects bare soil from erosion. So what is green manure? A cover crop becomes green manure when it is incorporated into the soil to improve soil fertility. Green manure is, therefore, a cover crop that serves as both a mulch and a soil amendment.
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Austrian winter peas (Pisum sativum subsp. Arvense) are one of the most common cover crops for gardens in winter because they are well adapted to cold temperatures. Some of the benefits of winterizing your garden with a cover crop of Austrian winter peas are:
1. Minimizing soil erosion.
2. Building soil organic matter.
3. Increasing the soil’s nitrogen content.
4. Reducing soil compaction.
5. Encouraging earthworms.
6. Controlling weed growth.
7. Disrupting insect and disease cycles.
8. Providing early spring nectar for honeybees
Growing Field Peas as a Cover Crop
Austrian winter peas, also known as field peas or forage peas, may be purchased at nearly any farm store by the pound or by the bag. For a garden large enough to use one or more 50-pound bags, that option is generally cheaper per pound. And any peas you don’t use this year may be saved to sow next year.
Although winter peas are related to garden peas, they are not grown for their fresh green pea pods. Instead, wildlife managers use them to create food plots for deer. Farmers use them as livestock forage and also as part of planned crop rotation. Organic gardeners grow them as green manure.
Like other legumes, winter peas capture nitrogen from the air and “fix” it in a form plants can use. In healthy soils, they fix nitrogen with the help of naturally occurring rhizobium bacteria. Where peas have not been previously grown, inoculating them with Rhizobium leguminosarum helps assure good nitrogen fixation.
The process of inoculation is quite simple. Rhizobium leguminosarum comes as a powder in which the pea seeds may be shaken before being sown. Or the powder may be sprinkled over the soil after the seeds are scattered. The more bacteria you use, the better it works. As the peas grow, the bacteria bond with the roots and produce the nodules that are responsible for fixing nitrogen.
Austrian peas prefer well-limed, well-drained clay or heavy loam soil of moderate fertility and near-neutral (6.0 to 7.0) pH, but they adapt pretty well to a wide range of soil types. Each fall, after clearing our garden beds of the season’s final crop, we liberally scatter peas over the soil. Since these peas are long-vined, unless they are seeded fairly thickly the growing plants tend to fall over against the soil and rot.
After we scatter the peas we cover them with about an inch of loose soil. Alternatively, they may be raked in to incorporate them into the soil. Peas left on the soil’s surface will not germinate well. They need adequate contact with moist soil, which also provides better anchoring for the roots of the growing plants.
If rain is predicted, we let the rain give the freshly sown peas a good soaking. Otherwise, we water them well and then let nature run its course. In a week or less the peas start to sprout, and within a couple of weeks, our garden beds are covered in a sea of green.
When to Sow Field Peas
To maximize winter survival, Austrian peas should be sown early enough for the vines to be 6 to 8 inches tall before the soil freezes. Since they are sensitive to heat, they must be sown after the heat of summer has passed. But as soon as the weather turns cool and moist, they grow rapidly.
Here in zone 6, we try to get our garden covered during September and October, although fall-harvested vegetables sometimes delay sowing the cover crop into November. As long as the peas sprout before the soil freezes, they will grow. If, as often happens in our area, we have a hard freeze followed by a period of warm weather, the peas just come up a little later than usual.
In zones 8 and 9, delay sowing until mid-October. In zone 5, try to get them sown between mid-August and mid-September. Although Austrian peas don’t consistently overwinter in areas colder than zone 6, your garden will still benefit as long as they have grown a good stand before freezing weather arrives.
When temperatures dip below freezing, the vines may lose some of their top growth, but they usually continue to grow even at temperatures as low as 10°F. However, long periods of cold below 18°F without a snow cover typically results in winterkill.
Whether the peas succumb to winterkill or survive into spring, they serve their intended purpose. Plants that freeze into a mat covering the soil’s surface act as a mulch, retaining moisture and retarding weed growth. Plants that remain green outcompete spring weeds, provide an abundance of early greens for our chickens and dairy goats, and produce beautiful purple blossoms that attract honey bees at a time when little else is blooming.
Preparing the Spring Garden
In years when our peas freeze to form a mulch mat, we rake the dead vines off the soil’s surface in the spring and toss the residue into the compost pile. The roots are left to rot in the ground.
Peas that survive into spring grow rapidly to a height of two to four feet. The slender, hollow, succulent plants are easily killed by snipping them back to ground level, by mowing them or by shallow cultivation.
When allowed to mature to full bloom, besides serving as one of the earliest bee-loving plants, vines that are then incorporated into the soil decay rapidly and contribute a quick source of nitrogen for the vegetable crop that follows. If we don’t need a particular garden bed right away, we’ll let the peas continue maturing until they produce seed, which we harvest to use for next winter’s cover crop.