Chapter 13. Special Soil Mixtures

Pick up any British gardening publication of the past two decades and chances are you will see something about John Innes Composts. Developed between 1934 and 1939 at the John Innes Horticultural Institution, these special mixtures of soil ingredients have been pretty well standardized as growing mediums for seedlings and pot plants. So sacred are they to gardeners in England (where the mix­tures are sold pre-packaged) that I suspect my comments about them will earn me a disapproving look or two. In spite of the public adulation given these mixtures, I believe the specialists who devel­oped them will agree with me that they were never intended to be the ultimate, perfect blends for growing a wide range of plants.

Reading between the lines, my guess is that what the scientists were really striving for were standardized, uniform growing me­diums that would always respond in the same way. These were de­signed for scientific research, so the factor of soil could be consid­ered an invariable in all tests. As can be appreciated, when a scientist tries to check differences in the qualities, functions or responses of plants, one thing he must have is a uniform environment.

John Innes Composts are nothing more nor less than standard soils for research work and should be considered in that light. That they work out well as seed growing and potting mediums is a happy by-product, which has led to a much wider use than I am sure was intended at first.

Here are the formulae for two of these special composts:

Seed Sowing Compost

3% parts (by volume) coarse sand;
3% parts (by volume) peat, and
7 parts (by volume) composted medium loam.

To each cubic yard of the above, add and mix in thoroughly two pounds of superphosphate (18 per cent phosphoric acid) and one pound of chalk (calcium carbonate).

Potting Compost

2 parts (by volume) coarse sand;
3 parts (by volume) peat, and
7 parts (by volume) composted medium loam.

To each cubic yard of the above, thoroughly incorporate the following:

Two pounds hoof and horn meal (13 per cent nitrogen);
Two pounds superphosphate (18 per cent phosphoric acid);
One pound sulfate of potash (48 per cent potassium), and
One pound chalk (calcium carbonate).

There are several obvious disadvantages to such mixtures. Me­dium composted loam would not be a uniform product by any means. Workers at John Innes might use loam from the same field each time, but chances of others matching this in other locations would be rather remote. Coarse sand in one man's language might be something approaching gravel in another's. Some ingredients might be difficult to find: I had to buy chalk at drugstore prices to run tests on these composts. And most gardeners would find hoof and horn meal hard to obtain. Also, original John Innes formulae call for steaming the first part of each mixture before adding other ingredients, a difficult operation for home gardeners.

Another standardized growing medium on sale in England is made up of two parts (by volume) of peat, two parts fine vermiculite (equivalent to the size used as a plaster aggregate in this country) and two parts kaolin clay. To a bushel of this mixture a fertilizer is added (8 oz. in all) made up of two parts magnesium sulfate, two parts potassium nitrate, three parts ammonium sulfate and four parts superphosphate (all fertilizer ingredients are by weight).

In Sand and Peat

A method of growing all kinds of plants in sand and peat was developed in the greenhouses of Vaughan's Seed Company, Western Springs, Illinois, and has been continued by Frank McFarland at Half Day, Illinois, following the razing of the Vaughan range sev­eral years ago. In this system, the greenhouse benches are packed with a mixture of sand and peat which serves largely as support for the plants; nutrient elements are provided by flooding the benches with fertilizer solutions. Frank McFarland uses nothing else to grow his superb greenhouse chrysanthemums. (He cuts a crop of blooms every day in the year on an exact schedule, and they command premium prices on the cut flower market.) This method of growing plants to maturity would be difficult for the amateur greenhouse owner, but is ideal for starting and temporarily growing seedlings, either in the house in a sunny window or in coldframes, hotbeds and home greenhouses. The following modifications have been worked out for amateur use:

Use clean (new or sterilized) flats, pots or greenhouse benches. The new "root-through" peat-and-fiber composition pots can be used without sterilization. Fill whatever containers you use with one of the following "soil" or growing mixtures:

1. 50 per cent Swedish, German or Canadian peat, plus 50 per
   cent sharp sand



2. 50 per cent Swedish, German or Canadian peat, plus 50 per
   cent horticultural-grade vermiculite (Terralite)



3. 50 per cent Swedish, German or Canadian peat, plus 50 per
   cent Perlite

After filling the container with growing medium, soak with plain water; allow the soil mixture to settle before sowing seeds. After sowing, cover growing unit with one of the plastic bags used to cover freshly-pressed clothes or with other thin plastic film. Often, the container will not have to be watered again until seeds germinate. After germination, water once with a soluble complete fertilizer such as the following trade-name products: Rapid-Gro, Plant Marvel. Use one level teaspoonful to one quart of water.

The U.C. System

One of the most complete methods for using special soil mixes ever developed is described in the publication "The U.C. System for Producing Healthy Container-Grown Plants," by Dr. Kenneth Baker, available for $1 from the University of California, Los Angeles 24, California. The publication recommends a system of growing plants which gets around the defects of John Innes Com­posts and also describes methods for overcoming diseases, pests and other problems. While primarily for commercial growers, the U.C. system should be of great value to anyone working with the special problems involved in growing plants in containers.

As stated, it is almost always advisable to sterilize soil (and pots, etc.) before use. This is most commonly done by steam (heat) or by chemicals. With any of the several chemical sterilants now on the market, be sure to follow package directions exactly.

 

SPECIAL SOILS FOR ROSES

Fortunately, some of the furor over special soils for roses has died down. I can recall a time when mere mention of that subject was an invitation to bitter arguments.

At the moment, the cow-manure-and-clay school seems to have lost out completely. I have not seen this system of growing roses mentioned in any article for the past year. (At one time, at least 95 per cent of all articles on roses included an admonition that if you wanted to grow the Queen of Flowers, you'd better have clay soil and be prepared to beg, borrow or steal several yards of cow manure. If you didn't, you risked being boycotted by all right-thinking rose lovers.)

Cow manure lost out to ordinary fertilizers when that ambrosial product disappeared from within easy reach of city gardeners. Rose growers on or near farms still use it as one of their special privileges. I can't pretend that I am not envious, or that I scorn it. At the same time, I am not unaware of the fact that persistence of blackspot fungus in many a manure-fed garden can be traced directly to sur­vival of spores in a cozy bed of damp cow manure over winter.

Persistent Clay

The preference for clay in rose beds has persisted longer. Even today, the notion that roses prefer clay pops up from time to time in print. An amusing item of contradictory advice appeared in a recent encyclopedic English book on roses. In one chapter the author advises against firm planting of rosebushes, while in another chapter he says he favors clay soil.

If truth be known, roses will survive in almost any soil, from a sandy loam to a stiff clay, so long as they have all the food and mois­ture they want. Actually I would say the lighter the soil the better the root growth. The most vigorous roses I've ever seen are volun­teer Rugosas that stand eight feet high in a grove that covers half an acre. The plants have stems 2 inches through at the base. This grove is in pure sand at the edge of a swamp but is fed by runoff from a richly organic meadow higher up.

When we speak of roses, most of us mean the modern hybrid tea which, as one outstanding authority described it, "is a damned poor excuse for a shrub." We must remember that the rosebush of com­merce is grown (grafted) on an understock which was selected as much for the convenience (ease of propagation) and profit of commercial growers as for its vigor and ability to recover after transplanting. The understock Rosa multiflora japonica has one weakness; it regenerates new roots so poorly after planting that sometimes a year or two is needed to allow it to make an adequate new root system. To illustrate: I dug up some rosebushes which had been planted in clay two years before. I found the bushes had made few roots and these few were stripped off in the digging operation. The same varieties planted in loose, friable Gardener's Loam not only grew plenty of new roots but made 25 per cent more top growth.

A Few Tough Problems

There are very few soils that will not grow good roses. Thin whitish and gray clays found occasionally on older farmlands in the East, pure sands without any organic matter, and the alkali soils of the West present problems too difficult for most gardeners to try to overcome.

Otherwise, any soil can be made suitable for roses. One proviso is to add all the organic matter you can afford, up to 25 per cent by volume. Provide good drainage and adjust pH to a reading between 6.0 and 6.9, and roses will grow.

One bit of nonsense to avoid with roses, unless time hangs heavily on your hands, is the old idea of digging out a pit 36 inches deep, laying down small rocks or broken bricks for drainage, adding a layer of organic matter and filling in with rich soil. I can't see any profit in such a deeply prepared pit for roses. Their roots are too feeble to take advantage of the improved soil depth; they probably would never get a chance to feed on that layer of organic matter buried 36 inches down. The 24-inch depth of double trenching should be adequate for the root growth of hybrid garden roses.

SOILS FOR ERICACEOUS PLANTS

Plants which prefer acid soils rarely need special soil treatment in areas where they grow naturally. When, however, the gardener in alkaline soil areas of the Middle West or California (to cite just two places) decides he must have azaleas, rhododendrons, blueberries or heather, a very real problem arises.

True, a soil pH as high as 6.9 can be pulled down with sulfur to 5.0 to enable such plants to survive. But maintaining such an acid soil in an alkaline area is often another matter. Surrounding soil will continue to be alkaline in reaction, and unless the site selected is on higher ground than the rest of the area, water runoff draining into the treated soil will bring in alkalinity to undo the gardener's efforts. Domestic tap water will usually be alkaline with a pH as high as the native soil or higher. This is particularly true in limestone country where ground water filters through limestone strata.

Among the worst offenders are earthworms (see Chapter Ten). They prefer an alkaline soil or at least one less acid than will sup­port ericaceous plants. Even though the native alkaline soil is re­moved to a depth of two or three feet and replaced with earth high in acidifying materials, earthworms will continue to burrow through this to reach the surface. Their burrows will be lined with limey slime brought from lower in the subsoil. Since most soils for erica-ceous plants are high in organic matter, this helps feed the worms, which will pull half-decayed leaves, grass and other vegetation down into their burrows and mix it with limey soil to help digest it. I have seen a specially prepared area of rich acid soil ruined in two years by these pests.

The answer to earthworms is to dig out the pit to a depth of three feet and sprinkle chlordane over the bottom before refilling with acidified soil.

To counteract alkaline run-off into acidified soil, a ring or band of dusting sulfur perhaps a foot wide can be laid down around the treated area; drainage water must run through this sulfur strip.

Domestic water does not usually contain very much suspended matter, so if it is alkaline the amount of acidifying material needed to neutralize it is relatively small. Two ounces of sulfuric acid to 100 gallons of water is usually enough. If the planting is too large to be watered out of a barrel of treated water, there are devices which attach to the end of a hose; they withdraw a certain amount of sul­fur solution out of a special container and mix it with tap water passing through the hose. Working out proportions to deliver two ounces of acid in each 100 gallons of water is a problem in simple arithmetic, once you know the proportioning ratio of the hose device.

Instead of liquid acid you can use a solution of one pound of ammonium sulfate or two pounds of ferrous sulfate to 100 gallons of water. The latter also supplies iron, an element often lacking in acid soils. (Used in this way, ferrous ammonium sulfate is not harmful, since the direct-nitrogen-fixing bacteria which it suppresses are not active in acid soils.)

Regardless of the chemical you use, check the water coming out of the hose; be sure (when pressure is full) that it checks at or below the pH desired. Always use the same pressure, since a change may change the ratio.

Asparagus Soils

Not long ago I read a book which offered elaborate instructions for making an asparagus bed. The soil was to be dug out to a depth of two feet, then broken brick, cinders or other drainage was to be laid down, followed by an organic-rich soil mixture to fill the excava­tion. This was to be allowed to settle, after which trenches 12 inches deep were to be dug for planting.

I am all for deep working of soil if it will be occupied by the same plants for ten to twenty years or more, as an asparagus bed well may be, and if the deep digging will return adequate plant-growth div­idends. But asparagus will grow well in any ordinarily prepared garden soil.

Planting 12 inches deep is a waste of time for the asparagus crop and merely delays by at least a week the appearance of the first spears of the season, which, to my taste, are the best of the crop. No matter how soil is prepared, set crown tips not more than 2 inches down. We no longer want to grow blanched asparagus spears through six inches of soil. We no longer want to run cultivating equipment right over the crowns: today we use chemical weed killers. As for soil, any directions previously given for Gardener's Loam will pro­duce a soil amply rich for this crop. Some of the best-flavored asparagus I ever ate came from a prairie which hadn't been plowed or manured for 30 years; in fact, the plants were growing wild all over the field.

Chapter Digest

Sometimes a need arises for a growing medium with some particular qualities—whether the material is to be used for garden or indoor plants. Among the special cultural compounds for container-grown plants are the John Innes Composts of English fame, while peat and sand mixtures (supplied with liquid nutrients) are used successfully by American growers. In the garden, of course, different problems surround the creation and maintenance of special soil mixtures or conditions. The pros and cons of soils for roses and acid-loving plants are discussed in helpful terms.

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