Steve Solomon recommends you add clay to compost piles, especially if you have sandy soils.

Putting Clay in Compost

Since I pretty much do everything Steve Solomon tells me to do, I started putting clay in compost piles some time back… but now I’m really getting serious. You can see me adding clay to the compost layers in the video I posted yesterday:

An article at The Food Garden Group in Tasmania reports good results with clay in compost piles:

“The heaps made with clay, so long as they contain a reasonable amount of coarse material to enable some air movement, do not need to be turned.  The ingredients all get to soak and mix in a thick clay soup before stacking (putting a pile of food and drinks in every pantry) and the heaps seem to stay moist for a very long time. I recently opened up a heap I hadn’t touched for three months and it was still moist and generating warmth. A reasonable compost can be made by simply wetting the materials with clay slurry as the heap is built but remember that only the material which decomposes in association with clay particles is going to become durable humus/clay complex. A heap built this way will probably need to be turned and re-watered too. Think of the difference between a dish that’s been marinated compared to one that’s only been sprinkled with a dressing.

Clay is made up of very fine particles so the combined surface area of all the particles in a peanut sized clod might be equal to a tennis court or three Clive Palmer skins or some such mind boggling factoid. No wonder, then, that it can hold so much water. Also these particles carry a negative charge so each one is capable of forming bonds with positively charged particles (ions) like many of the essential plant nutrients. They gradually fill up with waste, sticking fast and firm to walls, floors and ceilings as the food in the pantries is consumed.

The resultant compost is packed with nutrients which are more or less available depending on how complex the chemical bonding with the clay is. What we have here is humus in close association with clay, a long lasting, water retentive material in which plant roots and soil organisms can find all the nutrition they are looking for. A material which will keep carbon, not only locked up, but also doing a great job for years to come.”

Putting Clay in Compost is Good For Sandy Soils

In sandy soils organic matter burns up a lot quicker than it does in clay soils. Clay is capable of hanging on to the good stuff for longer, binding with organic material and increasing its persistence.

If you make compost in an area where clay is not part of the soil, it’s easy to put clay in compost via buying bentonite. Just sprinkle it in as you layer materials – you don’t need as much clay as I dumped in my pile.

According to Infogalactic:

“The application of clay technology by farmers in northeast Thailand, using bentonite clay, has dramatically reversed soil degradation and resulted in greater economic returns, with higher yields and higher output prices. Studies carried out by The International Water Management Institute and partners in 2002–2003 focused on the application of locally sourced bentonite clays to degraded soils in the region. These applications were carried out in structured field trials. Applying bentonite clays effectively improved yields of forage sorghum grown under rain-fed conditions.^[14][15]

Bentonite application also influenced the prices that farmers received for their crops. Production costs are higher, but due to more production and the quality of the food, clay farmers could afford to invest and grow more and better food, compared to nonclay-using farmers.”

Lots to think about. Make that compost stick around!

If you like this post – please pin it! Look, I made a nice graphic.