Back in the spring of 1969, my first job was planting seedlings for Hrnak's Flowerland, the largest florist and greenhouse in Oshkosh, Wisconsin. Some mornings as I walked through the long greenhouses, I could smell the potting soil steaming out back -- like a 60-foot roll of dark, Boston brown bread baking all morning to perfection. It was a malty, indescribable, delicious smell. The "bakers" were two plantsmen who ultimately tallied 30 and 40 years respectively at Hrnak's. Art Muegge (whose father along with Marcel "Bud" Hrnak left the Sears estate in Chicago to start the florist business 70 years ago) and Irv Poeschel. They were joined by George Pensenstadler, a comparative youngster at age 60.
Their's was a mix I could not recreate nor buy in any commercial package. For 15 years I bought my potting soil from Hrnak's. Even when I lived 1,200 miles away; the soil became part of my return baggage when I flew round trip to visit relatives.
In 1985 the current owner, David Geurdon, made a bottom-line decision when he was offered a price for a commercial mix that cost less than his ingredients alone, much less added labor and electricity. Hrnak's stopped concocting its own soil. Now he buys about a semi truckload a year.
It was more recently I learned that the mix was simply 1/3 peat, 1/3 perlite and 1/3 topsoil. The secret, after all, must have been in the chocolately Wisconsin loam from the Zillges farm or some alchemy that turns steam and mere earth under heavy canvas to black gold.
Ever since, I've searched for potting soil that has, to my hand, the perfect crumbly texture that allows oxygen and nutrients to reach roots, balances water retention with drainage and gets my seedlings off to a strong start. Like most gardeners, I find that buying potting soil is an act of trust; you can't see what is in the bag and the company barely reveals the ingredients, much less the recipe. Often as not I either concoct my own from scratch or add a few things to the packaged variety, depending on what will be growing in it.
Last year I casually experimented with eight different commercial mixes most purchased by me, some sent by their manufacturers. They were Baccto Seedling/Propagating Mix, Earth's Best 1881 Select, Hyponex All-Purpose Blend, Gardener's Best Germinating Mix, Jiffy-Mix Soiless Mix, Moo Mix, Peters Professional Plant and Feed and Peters Professional Potting Mix. I found that, for mainstream, home garden seedlings, every one of the soils brought seed to transplant, sustaining them until they found their permanent home in the garden. Plant size differences were imperceptible when seed from the same packet was grown side by side in different commercial mixes. So for the basic seed starting, you can't go too far wrong picking up whatever the nursery sells.
That's not to say that the mixes are alike by any means. They differ dramatically in texture and somewhat in the way they react to water. I'm convinced that fine vermiculite-laden mixes are more appropriate for germinating flower seeds the size of glitter or for slow-germinating perennial seeds. Heavy mixes suit the coarser vegetables like tomatoes, which I want to transplant bearing a good-sized root ball, not some powdery coating that leaves a dusting of vermiculite as I move it. I found that the mixes with extra doses of fertilizer tended to harbor a bit of green mold. The fertilizer also boosted germination of small seeds so that too much thinning of fragile plants was required.
The whole commercial potting mix industry is only about 30 years old and may be on the cusp of a shift in priorities and opportunities as soil companies realize that the problem of too much solid waste can become a lucrative business in compost and soil amendments. It was 1962 when James Boodley and Raymond Sheldrake, Jr., then researchers at Cornell University in Ithaca, New York, developed soilless mixes because commercial greenhouse operators were losing their once plentiful resource -- clean topsoil -- to urbanization and herbicide contamination. They came up with a dozen formulas for greenhouse use, including for tomatoes, poinsettias, foliage plants and epiphytes.
The formula for seedlings and bedding plants is: 1/2 cubic yard of sphagnum peat, 1/2 cubic yard of vermiculite, 10 lbs. dolomitic limestone, 2 lbs superphosphate, 1/2 lb. calcium nitrate and 1/2 lb. potassium nitrate.
Known as the "Cornell Mixes" or "Cornell Peat-Lite Mixes," "there are over 35 soilless mixes on the market with the Cornell Mix as their basis," says the Cornell bulletin published in 1982 that lists the 12 formulas. Standard commercial soilless mixes contain peat and some combination of vermiculite, perlite, granular fertilizers, polymers, dolomite lime, wetting agents and charcoal.
In the past few years the trend has reversed as organic commercial mixes debuted in the marketplace. Organic mixes usually contain compost, perlite, peat and often manure and seaweed. Thomas Weiller, professor of greenhouse crop production at Cornell, points out that "peat, perlite and vermiculite are very stable materials. (You know what you're getting.) But compost is highly variable. It's difficult to come up with uniformity from a commercial point of view." And for home gardeners who buy soilless mixes and then boost them with their own homemade amendments -- as most of us do -- he observes, "if you add compost or garden soil to soilless mixes, you're adding all the weed seeds and diseases that the mixes were developed to avoid in the first place.
"Still, the whole idea of composting solid waste and getting out of it a product is an idea whose time has come," Weiller says. "We're ready for the industrialization of it."
Lately garden writers and a few gardeners have voiced concern over the horticultural industry's ecological ethics in using peat -- a resource that takes centuries to be renewed. The Canadian Sphagnum Peat Moss News Bureau and its public relations firm has replied by issuing press releases reports saying that the 20 million bales sold by Canadian in a year represents only .02% of the total Canadian peat reserves and that a restoration and reclamation policy has been set up. Reports admit that Canada's market share of global peat moss harvested is less than 1 percent. No one seems to be trumpeting the fact that mica, perlite, greensand and some other horticultural products are just as unrenewable.
With some European countries enacting legislation to preserve their peat bogs and prices increasing on peat, there's a search for peat substitutes. Rice chaff, coconut husks (called coir) and cocoa bean residues have been explored by other countries as alternatives to peat. Back to Earth Resources, Inc. of Dallas, Texas, is manufacturing composted cotton burrs, which have the soil-building properties of peat plus 10 times its nutrient content. "Our product is cheaper than peat and easier to wet and rewet," says Janice Williams of Back to Earth. The company tests the product for pesticides and only uses cotton not sprayed with arsenic or sodium chlorate defoliants. Cotton burr compost has not been used specifically in potting mixes but is sold in 11 Southwestern states as a soil conditioner and top dressing. The University of Florida is researching the potting mix ability of Melaleuca quininerva, a tree that has become a weed on more than 500,000 acres in the state. Most of these products won't be on your local nursery shelves, and if they do ever arrive in the U.S., expect some to be more expensive than peat. If you have decided to take the peatless route, you might press into service your own premium blend of compost, or better yet, composted leaves -- for a lighter ingredient -- in homemade recipes calling for peat.
Horticulturist Charlie Nardozzi and assistant Peter Horvath prepare some 70 cubic feet or yards of potting each year for National Gardening's greenhouse, GrowLab experiments and test gardens surrounding the offices, and like the rest of us, they have their own variations. Horvath finds "all of the commercial mixes are too dense -- this can lead to daming off," so he buys a mix and "adds another 20% to 30% by volume of perlite or vermiculite.
Nardozzi has his own concoction that reflects his organic goals. It's 2 parts vermiculite, 2 parts perlite, 3 parts topsoil, 3 parts peat, 2 part cow manure and 1/2 part bonemeal.
My own variation on my favorite Hrnak's blend is 1 part peat, 1 part perlite, 1 part compost, 1 part bonemeal. I've also found that commercial worm castings add a good texture and some organic fertilizer.
If you find a brand that works well, stick to it. I haven't found any really terrible commercial mixes and most packages claim to be guaranteed free of insects, disease and weed seeds, but I have heard of gardeners who swear there were weed seeds or damping off spores in their mixes. Also, don't reuse soil from, for exampl, last year's hanging baskets or potted pansies. A bad batch of soil will set you back at least two weeks.
What is this stuff in my potting soil?
Bonemeal or Bloodmeal. Organic amendments added to fertilize the mix.
Charcoal. Additive to absorb toxic agents.
Compost. Decomposed vegetative material containing nutrients. Holds moisture; adds weight, nutrients and microorganisms to the mix.
Composted Bark. Lightens the mix.
Dolomite Lime. Limestone sometimes added to acidic mixes to bring the pH to around 6 and boost growth.
Granular Fertilizers. Wide range of chemical fertilizers used to boost germination and feed seedlings during their stay in close quarters.
Leaf Mold. Parially decayed leaves (one to two years). Adds texture, increases drainage, can add acidity to the mix.
Manure. You know what it is. Usually well aged or commercially prepared cow variety.
Peat. Decomposed sphagnum moss and other reeds and sedges (brown peat) or peat humus (black peat) harvested from bogs and dried. Aerates mix and retains water while at the same time improving drainage.
Perlite. A heat-treated lava rock, used for lightening and aerating mix and improving drainage by shedding water.
Sand. Coarse-grade, builders' sand (also called sharp sand) used to balance the light ingredients and increase the flow or water through the mix.
Seaweed. Various types used as fertilizer in organic mixes. - Vermiculite. Processed form of the mineral mica, used for absorbancy and aeration. Breaks down more quickly than perlite.
Observations on commercial mixes: Baccto. Excellent texture. Good mix of perlite and vermiculite, includes peat, lime "nutrients," trace elements, wetting agent. Black.
Earth's Best. Contains peat, composted pine back, compost, vermiculite, perlite, dolomitic lime. Very coarse. Visible perlite and sticks. Crumbly. Black.
1881 Select. Similar to Earth's Best/Earthgro. heavy, coarse, crumbly, black.
Hyponex All Purpose. Blend of peat, "organic vegetable matter," sand. This had the consistency and weight of gravel dust. Gritty and heavy.
Gardener's Best Germinating Mix. Blend of peat and vermiculite, "major and minor nutrients." Fine textured. High vermiculite content. No perlite. Brown.
Jiffy-Mix. Soilless mix contains peat and vermiculite Very find. Extra high in vermiculite. Brown.
Moo Mix. High proportion of peat, large chunks of perlite. Brown.
Peter's Professional Plant & Feed. Soil plus time-release plant food. Fine texture. Some vermiculite. Black.
Peter's Professional Potting Mix. Seems to be the same mix as above without the time-release plant food.
Nardozzi's Own Orgainic Blend 2 parts vermiculite 2 parts perlite 3 parts topsoil 3 parts peat 2 parts cow manure 1/2 part bonemeal
Author's Variation of Hrnak's Mix 1 part peat 1 part perlite 1 part compost (or leaf mold preferred if not too acidic) 1 part bonemeal 1 part worm castings (optional)
Cornell Soilless Mix for Seedlings and Bedding Plants 1/2 cubic yard of sphagnum peat 1/2 cubic yard of vermiculite 10 pounds of dolomitic limestone 2 pounds superphosphate 1/2 pound calcium nitrate 1/2 pound potassium nitrate
Copyright NGA
Reprinted with permission HouseNet, Inc.
Potting Soil
by Cheryl Dorschner