Protect Your Soil by Growing Winter Field Peas and Beans

18 September 2014, written by Benedict Vanheems

As summer turns to autumn and bare patches of ground begin to pop up all over the plot we're left with two options: plant and sow more for winter and the spring that follows, or do something with the newly exposed soil to keep it in good heart. A well-planned kitchen garden will of course maximise the use of space to produce the highest possible yield of fruits and vegetables. Inevitably, however, there will be fallow periods when the ground simply isn't in use; winter's when this is most likely to be the case.

Keep Soil Covered to Keep it Healthy

It is important to remember that soil isn't just an inert material in which we grow our plants. Living within each square foot of ground are literally billions of microscopic organisms, and the majority of these inhabit its top few inches. This living soup of bacteria and fungi is joined by a host of worms, beetles and other creatures that work in harmony to keep the soil in fine form and its nutrients readily available to your plants' roots.

Leave the soil completely bare over winter and you'll starve its occupants. The result is less-than-optimal growth the following growing season – something no-one wants! The solution, of course, is to cover it up with plenty of organic matter that will break down slowly over winter to nourish the soil and its inhabitants. Another solution is to grow a green manure, or cover crop, which will protect this fragile subterranean ecosystem and provide material on site to either dig in or chop down and leave on the soil surface as a mulch by spring.

With warmer weather waning, your choice of green manures is limited. Thankfully the best plants to grow for this purpose are among the most powerful in their soil-nurturing benefits. Field peas and beans won't just cover the soil up but will act as a shot in the arm for nitrogen levels while contributing plenty of roughage for soil structure.

Wonderful Legumes

Peas and beans are both legumes, a family of plants that also includes the green manures of clover and lupins. These wondrous plants can fix nitrogen into the soil thanks to a canny relationship with rhizobia (one of the soil's many bacteria) that form nodules on the plants' roots to secure nitrogen that those plants can then readily absorb. By cutting your peas and beans down before they flower in spring this extra nitrogen will be made available for future crops to encourage healthy leaf growth.

Field peas or beans sown in autumn will also limit the effect of rain on otherwise bare soil, which can create a hardened pan on the surface or, worse still, wash out nutrients. By competing against weeds during any warm spell they will maintain a 'clean' soil for spring's crop sowings. Field beans have the added benefit of helping to break up heavier soils courtesy of their extensive root system.

How to Grow Winter Field Peas and Beans

The nature of a green manure means you will want as much cover as possible, which means a very high rate of germination. Soil preparation is therefore as important as for any other crop. Sow the seeds as per the seed packet instructions – usually 5-10cm (2-4in) apart in rows spaced 20cm (8in) distant. In a temperate climate you can sow right up until mid-autumn, giving you plenty of time to follow on from late finishers.

Your green manure needs to be dug in at least two weeks before a new crop is sown in order to give all that organic matter time to start rotting down. You can speed this process up by chopping up the stems into as small pieces as you can manage – a sharp edge to a spade combined with a stabbing action helps with this. Pick a day when you've plenty of frustrations that need working out!

Always cut your field peas and beans down while the growth is relatively soft and certainly before they start flowering. Flower and pod formation rapidly uses up most of the nitrogen that's been diligently locked up by those rhizobia, so while it's tempting to let them grow on, you'll lose a lot of the benefit. Needless to say, avoid following on with more crops in the pea and bean family; nitrogen-hungry leafy crops such as cabbage are best placed for this.

Field peas and beans are incredibly generous green manures, providing a very cost-effective means of giving your soil a boost while maintaining its modesty over winter. Give your kitchen garden a little extra love this autumn and see what a difference it makes.

By Benedict Vanheems.