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How Much Compost Could Wood Chips Wreck; if Wood Chips Could Wreck Compost?


You Bet Your Garden
Question of the Week © 2019 Mike McGrath

Note: Hundreds of Mike's informative articles are available (in alphabetical order!) right here at the Gardens Alive website. To find Mike's answers to your specific garden problem, Click here and find your topic (like Weeds, Worms, Rhododendrons...) in our complete alphabetical archive of Questions of the Week.

How Much Compost Could Wood Chips Wreck; if Wood Chips Could Wreck Compost?

Q. Bethany in Montoursville, PA (just outside of Williamsport, PA--home of both the 'family newspaper' known as Grit and the Little League World Series) writes: "I have plants in several 'Square Foot Gardening' boxes that are seeing slow growth and yellowing of leaves--especially on the snap peas, but really on everything. I used "Mel's Mix", but where he recommends five different types of compost, I went with a yard waste compost with pine bark that my local garden center recommended. I'm fearing the worst--that the pine bark is tying up all of the available nitrogen--and that I'll have to start all over again."

A. The worst? Starting over in late June is hardly the 'worst', Beth. Late blight destroying your tomato and potato crop while infecting your neighbor's gardens is 'bad'. A 'helpful neighbor' spraying Round-Up on your beds is 'very bad'. A sinkhole opening under your squash plants is 'very very bad'. And a secondary gate to hell (the primary one, as everyone knows, is in Turin, Italy) opening up next to your habaneros (perhaps attracted by their heat) would qualify as 'very very, very bad'. Your situation is 'unfortunate' at best. Honestly, you don't even make the 'Legion of Substitute Plagues' list.

Now, let's drop back to praise the memory of the late Mel Bartholomew, creator of the Square Foot Garden method and a dear friend of mine. In brief, Mel's SFG method was to take an area--say four by four feet or four by eight--remove all the existing soil, replace it with "Mel's Mix"--essentially a container mix of light, loose ingredients like peat moss and perlite plus compost, frame it out as a raised bed and use lattice-work dividers to grow the plants in designated areas of one square foot per crop. Perhaps four lettuce plants in one square-foot grid, nine carrots in another, one to two peppers or eggplants in the third grid and a single small (determinate) tomato in the fourth.

This grid system appeals greatly to people who have modular minds; it also looks very attractive when done well. It is not--and this is one of Mel's best friends speaking--the ideal way to grow some plants (like pumpkins or full-sized tomatoes). But Mel was savvy enough to realize that despite a few drawbacks, this new system of gardening would appeal greatly to neat freaks; and that the most important part of the plan was the soil improvement. (Also: Mel was an engineer before he was a gardener and was always fascinated with grid systems, so he wrote what he knew and loved and wound up being the author of the best-selling gardening book of all time.)

Now--that thing about "five different kinds of compost". That actually came about through a conversation between myself, Mel and Dr. Frank Goin--a compost genius affiliated with the University of Maryland. We were trying to answer the question "what if the only compost available to a gardener was in bags at the local garden center?"

The answer--which came from a smart person (Mel or Dr. G; not me) was to purchase one of every different type of bagged compost that was available, take them home, open them up, smell them, feel them, look at them; maybe test them for weeds and herbicide residues (as described in this previous Question of the Week). If one brand seems infinitely superior, go back and buy more. If they all seem more or less the same, Mel and Dr. Goin suggested you buy one or two bags of each (or however much you need), mix them all together in a big pile and use the result as the compost portion of the famous "Mel's Mix." Although we did pick 'five bags' out of the air as an example, there's nothing magic about the number five; it could just as easily have been three or four.

Now--your compost and bark mixture. I first noticed this disturbing trend about a decade ago at a garden center in Annapolis. A company was marketing what they promoted as the best of both worlds--yard waste compost and wood chips mixed together. Yikes! I finally got them to admit that they had failed to make enough compost to meet pre-order demand and had added wood waste to make up the missing yardage.

As foolish as wood mulch alone is, its much worse mixed with compost, where, yes--it will certainly tie up the available soil nitrogen; stunting your plants' growth and making them turn yellow. There is no cure other than to remove all that material, pile it up someplace and turn it weekly until you can't see any wood anymore. Then it might be usable compost.

But the fact that your peas were the most affected makes me fear that the compost in this mix may also be contaminated with herbicides, as peas and beans are the canaries in the coal mine when it comes to the kind of herbicide poisoning that occurs when grass clippings from treated lawns are used to make compost. (Again, this previous Question of the Week describes a simple home test that will reveal is your compost is so contaminated.)

So: you definitely have uncomposed wood stealing nitrogen from your plants. The material you purchased could also have toxic herbicides in it. The first step is to follow the paper trail. Any large-scale bulk compost offered for sale is supposed to be tested. Ask for (or demand) those test results. At the very least you should be able to make the garden center reveal their source and follow the breadcrumbs back to the original supplier.

No matter what, you deserve reparation. Removal of and reimbursement for the junk "compost" you were sold, repayment for the peat moss, vermiculite and or perlite you added; and compensation for the plants you lost. You still have time to replant in a clean soil mix--but never buy compost that contains visible wood again.

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