Trench-Bed Gardening for Drylands

Does the soil where you grow your vegetables get hard and dry when there’s little or no rain? Is it difficult to grow vegetables because you don’t have extra water you can put on them to help them grow? Let me tell you how some farmers with these problems grow very good gardens, even in the dry season.

There’s plenty of moisture during the rainy season of course, so at that time when there’s lots of rain they do something special to hold the moisture underground for their crops to use after the dry season begins.

Here’s how they do it: they dig a deep trench and fill it with alternate layers of soil and organic matter. Organic matter they use is grass, manure, kitchen scraps and other things that will rot or decompose. After putting all that organic matter and soil into the trench, they now have a long mound where the trench was. They then plant their crops in the soil on top of the mound.

When it rains, the organic matter that’s in the trench soaks up water and holds it for a long time. This way plants can grow even in the dry season, using the moisture that’s stored in the trench.

At the same time, as the organic matter in the trench rots, it adds good plant food to the soil, — so the trench is also useful as a way to improve soil fertility.

Although some people make quite shallow trenches, deeper trenches are really better in places where the soil is poor or very dry. A deep trench can be used for several seasons. It can be any length; it just depends how much space you need for the things you are going to grow. The first time you try out a trench-bed garden, don’t make it too long.

It’s important that the soil and organic matter in your bed be loose so that any rainwater that falls will soak right down into the bed. Because of this, you must never step on your bed. Now, so that you won’t have to step on the bed and so that you can easily reach the centre from either side to plant or to weed or to harvest, it should be no more than 2 metres (6 feet) wide.

If the land where you grow your crops is sloping or hilly land, even on a gentle slope, be sure to dig your trench along the contour, that is, across the slope, not up and down.

Dig your trench 1 metre (3 or 4 feet) deep; that’s a good depth for your trench. If that’s impossible, it could be shallower. If some of the soil you dig out is better than the rest of the soil, it’s a good idea to pile the better soil separate from the poorer soil. Then, later, when you’re filling the trench with different layers of organic matter and soil, you can put some of the poorer soil in the lower layers and all of the better soil in the upper layers. Also, if your trench-bed is on a hillside, some of the poorer soil can be used for making a small bund (ridge) to help hold rainwater in the area of your trench-bed.

Now, after you’ve dug your trench, first lay down a thick layer of organic matter in the bottom of the trench, about 30 centimetres (12 inches) deep. This could include weeds and grass, crop residues and kitchen scraps, manure, bones, feathers and anything else that will rot or decompose as time passes. Then cover this with 5 or 10 centimetres (about 3 inches) of soil. The trench should now be about one-third full.

On top of this add a second thick layer of organic matter, about 30 centimetres (1 foot) deep, and again cover it with a thinner layer of soil.

Then add a third thick layer of organic matter, so that the trench is full right up to the top.

On top of all this spread a thick flat layer of good soil, or good soil mixed with compost, about 30 centimetres (1 foot) deep.

You now have a flat mound of good soil piled on top of three thick layers of plant material and other things that will rot. These layers are separated by thinner layers of soil. Although the mound is now about 30 centimetres (1 foot) higher than the original ground level, it will sink down as time passes.

The first crop you plant on your new trench-bed should be a legume crop, such as pulses, peas, beans, soybeans, stylo (Stylosanthes), sunnhemp (Crotalaria) or alfalfa (lucerne). Growing legumes adds nitrogen to the soil, and this is very good for the crops that grow there after the legume crop.

As soon as flowers appear on this first legume crop, the best thing to do is to dig it all into the ground. This will enrich the soil a great deal. If you allow this first crop to mature and you harvest it, the soil will be improved, but not as much.

Now you can plant other crops — vegetables, root crops, and even grains if you want to. It’s best to rotate the kinds of crops you grow on your trench-bed each season. Be sure to grow legumes again though, after two or three seasons. This will help to provide more good nitrogen plant food for the crops you grow after that.

After each harvest dig the crop residues back into the ground. Also mix in other kinds of organic matter, including kitchen wastes and manure. Adding this organic matter will keep the soil rich and help it to hold soil moisture.

There’s something else you can do to be sure the bed doesn’t dry out on top — you can mulch the bed. By that I mean you can cover the soil with grass, leaves or other organic material. That’s a very good thing to do.

One final thing: if your trench is dug across a slope, you should plant strips of a deep-rooted legume such as stylo (Stylosanthes), alfalfa (lucerne) or legume shrubs along the lower edge of the bed. This will help to stop soil from washing away during rainstorms.

In Zimbabwe they grow vegetables including tomatoes, and even peach trees on these trench mound gardens; and in the Philippines Miss Zeny Ubaldo showed me her trench garden and told me what she was growing in it.

We have sweet potatoes, also we have string beans, peppers, okra and beside that this camote and potatoes will be harvested after three or four months — and we have small seedlings and different seedlings of fruit trees.

Thank you very much Miss Zeny Ubaldo, the Director here at Bulacan Farmers Training Centre in Malolos in the Philippines.

Serving “Agriculture, the Basic Industry”, this is George Atkins.