Raised Beds Don’t Need Wooden Sides
Some years ago, I attended a workshop on wood safety, part of an environmental conference sponsored by a group called Beyond Pesticides. About 50 people were gathered for this workshop, which presented alternatives to wood preservatives like arsenic and penta. Some of the speakers were scientists who have spent years studying the effects of pressure treated wood on humans. As a result, they were trying to get laws on the books that would require the disposal of some common kinds of treated wood as toxic waste. Happily, they succeeded, at least to some degree, and today, treated wood must be disposed of through a hazardous waste facility.
Want to know more? Check out this link: http://www.ecy.wa.gov/programs/hwtr/dangermat/treated_wood_waste_disposal.html
What has this got to do with gardeners? One of the questions that stumped the experts was what to recommend to gardeners who wanted to make raised beds. As it turns out, many plastic woods release a low-volume but steady stream of contaminants into soil, water, and food growing in plastic wood lined beds. Most treated wood releases significant amounts of copper, arsenic, and lots of other less-than-healthy chemicals when exposed to water, whether rain or watering sprinklers. here in the maritime Northwest, that is a significant consideration, of course.
Low Wall Or No Wall
What’s a gardener to do? Well, how about nothing? I was delighted to hear one panel member declare that she has fed her large family for many years from a garden filled with raised beds made without any kind of siding at all. She also said that her kids survived just fine without penta-treated play gyms, swing sets, or sand boxes. This gal had been the first woman hired to climb power poles to repair the lines for a city east of the mountains.
Not knowing she was pregnant, she continued to climb as many as 30 poles daily through six weeks of a very hot summer. Her baby had and still, as an adult, has neurological deficits that her other children don’t share. These deficits match known symptoms of acute penta poisoning. Does it make sense, she wondered, to line our garden beds with this same material, which is now well documented as unsafe? The answer is clearly NO.
If Not Wood, What?
So what do you do? My suggestion has long been to make mounded rather than raised beds. Instead of preforming rectilinear shapes with wood or plastic, simple heap the fresh topsoil and compost into beds. If you use good soil and plenty of compost, the gently sloping sides will not erode at all.
If you like, you can plant the sides with creeping thyme, oregano, marjoram, hyssop, lavender, sage, and other hardy herbs. The herbs will knit together quickly, making a tidy, aromatic and attractive edging for your beds. Their pungent scents will help drive away pests and their flowers will attract bees and other pollinators.
No Till, No Kill
What about tilling? It’s extremely hard to till the soil in box-beds anyway, so why bother? We now know that the upper few inches of soil are alive. Why smother the biota under a heavy load of less-good soil in the tilling process?
If we don’t till, we also don’t kill off the soil life. Sounds good to me! Instead, layer on fresh amendments each season, blending or covering them with compost. If you want a particular amendment to reach the root zone of particular plants, add it when you plant or before seeding a specific area.
Sweeps And Curves
Beds made by this mounding method are easy to make from scratch and easy to maintain. If you really need straight lines, by all means, have them. However, mounding allows you to break the box, giving your beds graceful curves that echo natural ones. Personally, I prefer the shapes of angel wings and ellipses over geometric boxes, but by all means, make shapes that give your eyes pleasure.
Whatever their shape, the beds should be at least 5-6 feet wide and long. Smaller mounds will dry out too quickly to be useful. If you prefer larger shapes, use stepping stones to make a central path so you can reach every part of your bed without stepping on the growing areas.
Use Cover Crops
When your crop is harvested, use a cover crop like alfalfa, clover, or winter peas to add nitrogen to your soil. Chop the top growth and turn it under come spring. You can use the same technique with young weeds; turn them under before they can set seed and they simply melt into the soil, returning their nutrients to crop plants.
To avoid weeds altogether (or almost), use plenty of mulch. I often use mulches that combine compost and soil conditioners with corn gluten. The corn gluten is high in nitrogen, which helps plants grow faster. Corn gluten also prevents weed seeds from sprouting, which saves the gardener from weeding. Do remember that it doesn’t know a weed seed from a carrot; don’t use this mulch in the vegetable garden until AFTER your garden seeds come up.
Now Is The Time
Is it too late to make such a bed now? Not at all. Just be sure that the soil is mounded at least 18 inches deep through the bulk of your bed. That seems high at first, but as the soil settles, the heaps will shrink down quite a bit. Top your beds with two or three inches of compost or mulch, then plant away. If you are planting seeds, leave the seed strips unmulched until your seeds emerge. When the warm soil coaxes your seeds awake, snuggle the mulch in closer as the young plants grow.
The warm beds will boost your plant’s growth, and their roots will be getting plenty of the air they need. The mulch will help conserve moisture and keep the plant roots cooler as the summer heats up. Bon appetite!