In my last article, I talked about the problems with improving clay soil and amending sandy soil with sandy and clay, respectively.
The correct answer you’ve been looking for about amending soil is the same for both, and that is organic matter.
Compost is what I’m generally referring to. Amend soil with 6 inches of good compost. Work it right into the top of a clay soil and it will improve infiltration and will probably improve the amount of air and water available to your plants.
(I should mention that no amount of organic matter, rototilling and aeration will fix a serious drainage issue such as flooding. That needs to be addressed by installing drainage, or even better, work with nature and put in a pond.)
Back to compost. Amending sandy soil with 6 inches of good compost will drastically improve the water-holding capacity of the soil.
Amending clay soil with sand won't help, but compost will
Other Organic Gardening Implications
Since we’ve been learning about how water moves through the soil, I’d like to mention a couple of other important organic gardening implications of what we’ve learned about amending soil.
Take patio pots for example. Gardeners will often put a layer of gravel in the bottom of a container to improve drainage, but as we have seen it actually does the opposite. The soil on top has to be very saturated before the water will drain through. This is not necessarily a bad thing with the right plants, but it is important to know how this works.
The other main implication is with regards to organic matter. If you amend soil by turning in (burying) course organic matter such as leaves or straw and they end up buried in a layer, or if you drop 6 inches of soil on top of a big layer of course material such as sticks or straw, you could be creating a course layer underneath a fine layer.
This is the same situation where that soil will get very wet before water will drain out. If straw is incorporated very well, this will not occur, but if it is just turned under, it will.
If you need to bring soil into your yard in order to build your garden, you must make sure to rototill it in to the existing soil extremely well. If you just drop it on top, you are inevitably creating an interface that will slow drainage.
And try to find a soil that has a similar texture to your exiting soil (i.e. if your soil is clay, bring in more of a clay topsoil than a sandy topsoil). Also, use compost for perhaps 25% of the mix.
Is there anything organic matter can't do?
