The Dirty Little Secret of Raised Bed Success
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Q. Bernadette in Allentown writes: "I grow vegetables in raised beds. I start with organic plants and grow them organically using compost from the Rodale Institute as my added fertilizer. This year I have four new raised beds measuring 4 ft by 8 ft and 12 inches deep. My question to you is: What kind of soil do I look for that is as close to organic as possible? I can't use organic soil in bags; it's too costly for the amount I need. I hear that mushroom soil is probably treated with chemicals. I would really appreciate your advice on looking for soil to fill the raised beds."
A. The first thing I want to say is that you should always take the long view here. Depending on your age and Gods' Good Wishes, these beds could be producing--or not--for decades to come. So assume the 'amortization' aspect and presume that what you start with will be with you for a decade or two. Filling a bed is easy; emptying it and starting over is not.
The second thing I want to say is that there really isn't anything called "organic soil". But bagged potting soils, composts and the like that carry the OMRI seal of approval (Organic Materials Research Institute) have been tested and are approved for use on organic farms and gardens.
Now, you mention The Rodale Institute, a fine non-profit facility in Kutztown just a half-hour or so from Allentown; especially if you take I-78 instead of slowpoke Route 222. I spoke with Rick Carr, Farm Director and Compost Production Specialist for The Institute and he explained that they will have organic compost for sale this season. (Hey, if you hear the name 'Rodale', you can be pretty sure it's organic!)
They offer bulk compost at $35 per cubic yard; you must bring your own method of transport (pickup truck or trailer), but they will happily load it for you. (A cubic yard of compost equals 27 cubic feet. A raised bed that's four by eight by one foot would require 32 cubic feet of material.)
But I never recommend compost alone when filling a bed for the first time; it can get too heavy, especially in wet climes. For me, the perfect filler is around 50 percent compost, 50 percent high-quality screened topsoil and a generous amount of perlite (a mined volcanic glass that aids drainage and retains water, which is quite a trick!).
No garden soil unless you are certain that it contains no lead (this problem is extremely common in urban areas and anywhere near an older home; and working in lead contaminated soil can be extremely dangerous to the worker/gardener). If a lead test clears your soil, you can use it as a base to take up some room in the bottom of each bed. Do NOT mix it in; and two inches on the bottom would be the maximum. Then mix the other ingredients well, preferably in a wheelbarrow, and pour them on top of that wretched garden soil.
And since only half of the mix is compost, two cubic yards would seem sufficient to supply the compost component of your four raised beds. That's seventy bucks plus gas money. (And for those who operate on a smaller scale, Rodale sells bags of compost (each about a five-gallon buckets' worth) for five bucks; and they supply the (non-plastic) bags.
Before you buy topsoil (or non-Rodale compost) in bulk, go to the facility and get a bucketful to test. Place some of the topsoil in a regular old plant pot. Place some more into another plant pot. Leave the first pot unplanted but water it frequently. Sow some fresh seeds in the other one (pea or bean seeds are best as they are extremely vulnerable to herbicide poisoning, which is what we're testing for here) cover with some more soil and water frequently. Try and do this inside if at all possible, to keep the pots warm.
If the empty pot stays empty, you're good to go. If the empty pot sprouts plants, take a pass because the material is full of weed seeds. If your test crop comes up looking nice and green and happy and healthy, go for it. If they emerge all withered and nasty looking, take a pass, cause there's herbicides in there.
You should perform this simple test on every load of bulk material you're thinking about purchasing. Do not wait until it gets dropped off! In addition, give every batch the duck test: does it SMELL like good rich soil? Does it FEEL like good rich soil? And does it LOOK like good rich soil? If it smells like a duck, looks like a duck, and feels like a duck, it's just DUCKY!
There are numerous facilities all over the country that sell bulk compost, bulk topsoil and mixes of each. Some may even be able to supply you with the equivalent of a soil test for bulk compost, so always ask for the paper. But no matter what, take home a sample of any bulk material for testing BEFORE you buy.