What to Fill Your Raised Beds With
Q. Bernadette in Allentown writes: “I grow vegetables in raised beds. I start with organic plants and grow them organically using certified organic compost as my added fertilizer. This year I have built four new raised beds measuring 4 ft by 8 ft by 12 inches deep. My question is: What kind of soil should I look for to fill the beds that is as close to organic as possible? I can’t use {quote} “organic soil” in bags; it’s too costly for the amount I need. I’ve heard that mushroom soil is probably treated with chemicals. I would really appreciate your advice on looking for soil to fill the raised beds.”
A. You should always take the long view here. Raised beds that are constructed and filled correctly at the beginning should be producing excellent harvests for a solid decade or more without any kind of major overhaul. The amount of time you take thinking things through and the amount of money you spend on the contents will amortize over the next decade—IF you don’t rush your decisions or cheap out on those contents. Filling a raised bed correctly is easy; emptying it and starting over is not.
As I have stated repeatedly, there really isn’t anything you can buy in a bag or in bulk called {quote} “organic soil”. However, 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.
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 mix is around 40 percent compost, 40 percent high-quality screened topsoil and a generous 20 percent perlite (a mined volcanic mineral that aids drainage and retains water, which is quite a trick!).
Don’t be tempted to use your old garden soil. In addition to weed seeds, pests and pathogens like verticillium wilt, it could contain lead, an especially common problem in urban areas and anywhere near an older home, garage, roadway, railroad line, service station, etc. The danger is to you, not your plants. Lead contaminated soil can be extremely dangerous to anyone touching or inhaling the dust. And besides, that garden soil is what you’re escaping, not running towards!
Before you buy topsoil or compost in bulk, go to the facility and get a bucketful to test. Place some of the topsoil in two regular plant pots. Same with the compost. Leave the first pot of each unplanted but water it frequently.
Sow some fresh seeds in the other ones (pea or bean seeds are the best indicator of herbicide poisoning, which is what we’re testing for here). Cover the seeded pots with some more soil, water well and then stretch plastic wrap over the tops. Water as necessary to keep the soil moist. Do this indoors to keep the seeds warm enough to germinate.
If the empty pots stay empty after ten days or so, the material is weed-free. If the empty pots sprout plants, the material is full of weed seeds. If your test crop plants come up looking nice and green and happy and healthy, the material is clean. If they emerge all withered and nasty looking, there’s herbicide in that there dirt.
You should perform this test on every load of bulk material you’re thinking about purchasing. Do not wait until it gets dropped off! Once the material hits your driveway, you’re stuck with it. In addition, give every batch the duck test BEFORE YOU BUY. Pick up a handful. 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!
However, if it has any off odors, feels slimy or is soaking wet or crumbly dry, take a pass; it won’t get any better. Start your quest early, so you can take samples at a number of garden centers. If they are reluctant to give you any material for testing, offer them a few bucks and tell them your driveway is not quite finished enough to receive a big load, but you need some starter material for winter hardy plants. Or use the credible lie of your choice.
There are numerous facilities all over the country that sell bulk compost, bulk topsoil and mixes of each. Municipalities and larger garden centers should be able to supply you with the equivalent of a professional soil test for bulk compost, so always ask for the paper. But no matter what that paper says, take home a sample of any bulk material for testing BEFORE you buy.
Oh—and there are at least four different kinds of {quote} “Mushroom soil”: fresh and aged regular; and fresh and aged organic. The differences are important and will take another Question of the Week to fully explain, which we plan to do when you join us again, same Bat-Time. Same Bat-Station…
A. You should always take the long view here. Raised beds that are constructed and filled correctly at the beginning should be producing excellent harvests for a solid decade or more without any kind of major overhaul. The amount of time you take thinking things through and the amount of money you spend on the contents will amortize over the next decade—IF you don’t rush your decisions or cheap out on those contents. Filling a raised bed correctly is easy; emptying it and starting over is not.
As I have stated repeatedly, there really isn’t anything you can buy in a bag or in bulk called {quote} “organic soil”. However, 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.
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 mix is around 40 percent compost, 40 percent high-quality screened topsoil and a generous 20 percent perlite (a mined volcanic mineral that aids drainage and retains water, which is quite a trick!).
Don’t be tempted to use your old garden soil. In addition to weed seeds, pests and pathogens like verticillium wilt, it could contain lead, an especially common problem in urban areas and anywhere near an older home, garage, roadway, railroad line, service station, etc. The danger is to you, not your plants. Lead contaminated soil can be extremely dangerous to anyone touching or inhaling the dust. And besides, that garden soil is what you’re escaping, not running towards!
Before you buy topsoil or compost in bulk, go to the facility and get a bucketful to test. Place some of the topsoil in two regular plant pots. Same with the compost. Leave the first pot of each unplanted but water it frequently.
Sow some fresh seeds in the other ones (pea or bean seeds are the best indicator of herbicide poisoning, which is what we’re testing for here). Cover the seeded pots with some more soil, water well and then stretch plastic wrap over the tops. Water as necessary to keep the soil moist. Do this indoors to keep the seeds warm enough to germinate.
If the empty pots stay empty after ten days or so, the material is weed-free. If the empty pots sprout plants, the material is full of weed seeds. If your test crop plants come up looking nice and green and happy and healthy, the material is clean. If they emerge all withered and nasty looking, there’s herbicide in that there dirt.
You should perform this test on every load of bulk material you’re thinking about purchasing. Do not wait until it gets dropped off! Once the material hits your driveway, you’re stuck with it. In addition, give every batch the duck test BEFORE YOU BUY. Pick up a handful. 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!
However, if it has any off odors, feels slimy or is soaking wet or crumbly dry, take a pass; it won’t get any better. Start your quest early, so you can take samples at a number of garden centers. If they are reluctant to give you any material for testing, offer them a few bucks and tell them your driveway is not quite finished enough to receive a big load, but you need some starter material for winter hardy plants. Or use the credible lie of your choice.
There are numerous facilities all over the country that sell bulk compost, bulk topsoil and mixes of each. Municipalities and larger garden centers should be able to supply you with the equivalent of a professional soil test for bulk compost, so always ask for the paper. But no matter what that paper says, take home a sample of any bulk material for testing BEFORE you buy.
Oh—and there are at least four different kinds of {quote} “Mushroom soil”: fresh and aged regular; and fresh and aged organic. The differences are important and will take another Question of the Week to fully explain, which we plan to do when you join us again, same Bat-Time. Same Bat-Station…
