Friday, 20 March 2009

How do you improve clay soil?

This is a question I've been asked quite a bit lately, and it seems to be a common problem in many gardens. Put simply - clay soils have a very strong bond with water, and tend to get waterlogged, with very little space for oxygen for the roots to breath. The result being, that rot can set in very quickly, or at the least, plants tend to look unhappy and become diseased easily.

The simplest solution would be to 'soften' the soil by adding coarse sand (as much as is possible). The shape and size of coarse sand leaves lots of gaps for air, and makes the soil less 'sticky'.

Another way to fix clay soils, would be to add large amounts of compost or well-decomposed organic matter - this does the same thing as adding sand, but it will also improve the soil's fertility at the same time. The only problem is that you would need to add quite large quantities to see the equal 'softening' effect.

Also, bear in mind that clay soil compacts very easily when wet, and doesn't bounce back up the way sandy soil would. Because of this, make sure that when the soil is wet that you try to walk or run wheelbarrows over it as little as possible.

2 comments:

ryan said...

This is a big topic. We get this question all the time, too, and our first answer in part is to improve our plant choices rather than the soil, but no one seems to fully accept that answer. "We're going to fill your garden with bog sage, ma'am."
We have very heavy clay soil in the San Francisco Bay Area, a lot of it ruined by people driving trucks over it and so forth. Most frequent comment by new employees when they plant, "I could make a pot with this stuff!"
Our clay soil tends to bond with sand particles and make "waterproof soil." Probably the most effective soil amendment around here is pumice, because the large porous particles aerate the soil and they're high in iron, but it's expensive. We tend to top dress with sometimes compost and always fir bark mulch, let the microbes aerate the soil for us, and in the meantime plant the clay lovers. A few of our natives absolutely eat the stuff up.

Anonymous said...

I have had success using gypsum and lots of organic material. Once the soil softens a little green manure also seems to help by putting roots into the soil which die and compost when you dig the green manure in at the end of winter, before you plant your spring vegetables.

Clay soils are very water sensitive; too dry and you get concrete, too wet and you can't get the sod to drop off your spade.

To begin with, I do not even try to dig the soil. I just swing a mattock into it and create some big cracks. I then add gypsum and a dry old manure and then a good garden soil covered with plenty of straw. The first year I plant my veges straight into this and hope for the best.

The following year I can usually get a fork into the mulch. I then repeat the gypsum and compost and plant a green manure around April (southern hemisphere). Around July I turn in the weeds with a fork and add more compost and straw.

The third year, the soil is nice and crumbly. By then I usually move into a new area of raw clay and create another garden bed. I sometimes plant fruit trees in the old bed.

By the time I am 106, I should have covered the whole block.

Related Posts Plugin for WordPress, Blogger...