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I am in the process of building 35sqm of beds. The beds will be raised to 20cm high using besser blocks. Unfortunately the soil were I am has a lot of clay. In fact it seems like it would be better suited to ceramics :-). I have read enough to indicate that clay soil can be improved but I have a few questions:
How long would it take to improve clay soil to a standard I can grow vegetables in including root veg like carrots?
What is involved and what sort of expense would I be looking at?
Finally, would I be better off trucking in some quality soil instead?
Clay is indeed a good base for growing food. Good soil is a mixture of sand, clay and organic matter. So you have clay. I suggest loosening the clay if possible and digging some sand into it. Be quite generous with the sand. Make sure its not beach sand which would have salt in it. River sand is the best. Then grow a green manure grow on the bed. Check out my blog and movie a few weeks ago about growing green manure crops.
This green manure crop will give the soil more organic substance. You then have a base to start growing food, ie clay, sand and organic matter. Over time these three will combine more and more to generate a growing layer of loam. The loam is really the result of the life process going on in this mixture of substances.
The cost of doing all of this will be minimal as long as you don;t pay too much for sand. Green manure crop seeds are very cheap, for example, I bought enough for 1000m2 from greenharvest.com.au and it cost $30 including postage. You can buy smaller quantities.
With regard to carrots, they prefer soil which is more sandy, so you will probably need to wait a bit before growing them. Carrots are not the easiest crops to grow. I suggest starting with easier crops requiring less soil fertility. One of the searches in our gardener subscriber site allows you to search crops by ease of growing.
Please keep us posted on how you progress.
Thanks for the reply Peter; I have a few more questions:
How much sand should I add per square metre? I have heard that adding too much or the wrong sand can make the situation worse.
In addition to green manure crops should I be adding other composts e.g. cow, horse, or mushroom?
How long will it take until I have useable veg beds?
With the sand, try a shovel full per m2. If its river sand, this should be OK.
It certainly good to add animal manures. They should really be composted before you plant food crops in them, but if you mix the sand, manures and some wood ash (important for potassium in the soil which lots of vege's like, have a two shovels per m2), then plant your green manure crop and let the green manure crop grow up to max height before seeding. Cut it down and leave bed for a month then plant. This whole process should take about 8-10 weeks, so from now you should have your bed ready by May.
At the same time it would be good to get a composting process underway so that you have some nice compost when you are ready for planting your veg.
It would be simple to go out and buy soil, but "first grade" soil is rarely what its marked as, you may import weeds and if you go that way, you won't learn anything yourself about the wonderful process of creating healthy soil which is the bedrock of any successful food garden.
Thanks again Peter.
Point taken on the imporance of learning how to create healthy soil.
I will follow your advice and let you know how it goes.