Square Foot Gardening Project: Step 2, Making Dirt

| 4/12/2011 9:37:25 AM

A photo of Allan DouglasIn this, the second installment of this series, we will make the “dirt” or Mel’s Mix needed to fill the boxes we built last time.  Mel’s Mix, as stipulated by Mel Bartholomew, author of All New Square Foot Gardening is made up of equal parts peat moss, compost and coarse ground vermiculite.  The peat keeps the mix “loose” making it easy for plants to grow and develop roots, the compost enriches the mix; providing lots of nutrients for the plants, and the vermiculite holds water; making it available to the plant roots for a longer period than regular soil would.

A truck load of dirt makking suppliesThe first order of business in this dirt making project is to visit the local garden supply store.  No, that’s not true; the FIRST order of business is to locate a garden supply store that carries the commodities we will need, and preferably in the quantities specified in the book.  And this is where the problems started for me.


First off, call the local garden centers and ask if they carry the compressed peat, course ground vermiculite, and multiple brands of compost.  Compressed peat (according to Mel) should expand to twice its volume when removed from its bag.  Course ground vermiculite does a better job of storing water than medium or fine, and because this stuff is expensive, buying it in the big (4 cubic foot) bags will save money.  Compost is made by breaking down vegetable matter with aerobic bacteria.  If you have a large compost pile of your own, you may use that instead of buying compost.  But you want to be sure your compost is “done” before you use it.


I started making compost from leaves, lawn clippings, kitchen waste (vegetable and rinsed egg shells only - no animal waste) and fireplace ash last spring.  I learned quite a bit along the way.  There are three major concerns to watch as you make compost; 1) keep the pile moist, but not wet.  A little water helps the bacteria grow, too much turns the pile into s sodden, stinking mess. 2) Aerate the pile by turning the pile with a pitch fork or by using a tumbler; the bacteria you want to cultivate needs oxygen to live.  If oxygen is not available, the aerobic bacteria dies and anaerobic bacteria begin breeding.  Anaerobic bacteria will produce compost too, but they take much longer and smell like a garbage dump while they do their work.  And 3) allow the compost to “cook” until the material is a rich, crumbly, black matter.  The inside of a compost pile will reach 150° Fahrenheit, which is hot enough to kill weed seeds if kept at that temperature long enough.  Also, mixing compost that is not done composting into your garden soil can kill your plants because the bacteria that are “rotting” your compost will attack the roots of plants growing in it as well.  Once the process is completed, this is not a problem. 

Commercial compost is usually made from a single source for each brand of compost.  Brand A may use the cast-offs of a mushroom farm to make compost, Brand B may use the hay and manure from a dairy farm barn, Brand C may compost saw-dust from a mill.  All are fine, none are complete.  Mel recommends mixing a blend of at least five brands of commercial compost to get the best nutrient mix.

If you make your own compost, get a wide variety of materials to go into it.  Yard clippings, fall leaves, kitchen scraps, and expended plants from your garden (except nightshades: eggplant, peppers, potato, tomato) are all excellent fodder for your compost mill.  You can add horse or cow manure (but not dog or cat poo) for added richness.  If you know a woodworker, sawdust can be added too, but avoid black walnut if at all possible, black walnut trees produce the chemical juglone in their root systems that kill certain families of plants, and this chemical will be present in the wood produced from a black walnut tree as well.  Common garden vegetables that will not grow within 50 feet of a walnut tree, or in soil containing juglone are cabbage and other cole crops, peppers, tomatoes, eggplants, asparagus, rhubarb and potatoes.  For details, Read This.

Kris Williams
5/17/2011 7:49:31 AM

I use this method all the time and although I am just a small gardener, this method works the best for me. However, I do not tend to have the extra money for the store bought barrier at the stores, I generally use newspaper (sometimes layered and/or with grass clippings - but NOT any colored inserts!!) and/or cardboard boxes (which my grocery store gives out boxes each week for free and I also use to line my garden paths with). And I prefer to purchase my local nursery's growing soil than any store bought supplies (cheaper and it is already mixed perfectly). Sometimes I think the article writer's get mixed up on buying items store bought to much, when you can do better with FREE or less costly items instead. Keep it in mind with this economy and high unemployment! ~Kris Williams

Nebraska Dave
4/13/2011 10:08:19 AM

Allan, wow such a lot of work for raised garden beds. Of course I have built an automatic watering system so I don't have to worry about soil water retention. My solution to all the soil mixing is just buy the city yard waste compost which is $30 a yard and fill up the 8 inch depth of the raised bed with it. It's all good rich black compost. Under the eight inches of compost I have another four inches of my fall lawn leaf grass mixture that has started decomposition over the winter. Your mixture of soil I use for my containers that need more water retention due to drying out faster. It does work but it's much more expensive. I wish you the best of luck with gardening this year. Always as with any thing gardening is all about preparation. Growing the vegetables is just enjoying all the hard labor of the spring. Have a great gardening year.

Cindy Murphy
4/12/2011 10:45:40 PM

Ah-ha! So that's where this recipe came from - "Mel's Mix". I remember last year a customer came into the nursery looking to purchase what seemed like an ungodly amount of vermiculite; he said he read about making his own soil, and needed equal parts of compost, peat, and vermiculite, (it seemed pretty cost prohibitive to me, actually). I think I might be able to shed some light on the expansion of the peat, Alan - if you already haven't discovered it. A compressed bale of sphagnam peat will expand to twice its size when opened, unlike bags of peat (which may or may not be sphagnam). Bagged peat will not expand because the product is usually pre-moistened. If you got dried sphagnam peat it should definitely expand...if not, try getting it wet, which is always a good idea before planting, as the dried product will suck any water away from your plants if not moistened first, (moistening it thoroughly is not as easy as it sounds). One word on compost, (and this is from someone who works at a nursery, so of course, it's biased): expecting one garden center or nursery to carry compost from five different manufacturers is asking a bit much, but next time ask if they have it in bulk also; if they do, you'll have at least two sources, (and bulk is less expensive than bagged). Good luck. Looking forward to reading more.

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