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9. Soils, Pots, and Potting

You will make bigger profits from your greenhouse crops if you plant them in the right soil mixture, in the proper kind of pot or other container, and shift or transplant them at timely intervals.

SOILS

The first-time greenhouse grower often faces the problem of finding organic material, an essential component of a light and rich potting soil. The usual recommendation is ⅓ garden soil, ⅓ organic matter (humus), and 1/3builder's sand. A com­post pile can supply the organic matter—or you can buy rotted manure to mix in the soil. Failing this, you can purchase bales of peatmoss or bushels of leafmold. Processed manure is also suitable.

Commercial growers obtain organic material in a way that may be adaptable for you. They cut sod and stack it in alter­nate layers, with manure and some commercial fertilizer spread between the layers. A man in my vicinity has some rather deep cold frames no longer used for plants. In these, he places a load of builder's sand, another of loam, and a third of brown peat. These materials are forked over until well mixed and allowed to age a year before use. You might try making up a similar mixture in a large wooden box or bin, or in a section of your cold frame. I think it is an excellent basic mixture, but I add special elements for various plants.

Any time is a good time to start a compost pile; the impor­tant thing is to have one. It will assure a reliable source of humus for little labor and less expense. Into your compost pile can go all kinds of vegetable matter: grass clippings, tree leaves, weeds, vegetable peelings, arid so on. If the pile is kept mois­tened and sprinkled with fertilizer or a special bacteria-activator as Activo, it soon becomes fine enough organic mate­rial for your potting soil.

Some gardeners dig a pit for compost; others prefer to have compost bins above ground. One manufacturer sells an alumi­num bin, 52 by 28 inches, that might suit your needs, especially if you are a city gardener.

When you consider that the small amount of earth packed into a pot must sustain a plant for weeks, months, or longer, you will see the importance of a good soil containing loam, organic matter, and sand. However, additions of sponge rock for greater porosity, charcoal as a sweetener, aluminum sulphate to acidify, or old mortar rubble (for cacti) can be beneficial for special crops.

The symbol pH is used to indicate the degree of acidity or alkalinity of a soil; pH 7.0 is neutral. Most potted plants grow well in a slightly acid soil with a pH of about 6.0 to 6.5. There are exceptions. Azaleas, citrus trees, gardenias, and hibiscus, do best in a definitely acid soil. You can purchase a soil-testing kit for your own testing, or have someone at your university or your county agent make tests to determine whether your soil is acid or alkaline, and what (if anything) it needs.

Do not use the same soil for more than 1 year. A sizable amount will go out every year with the potted plants, flats of seedlings, etc., you sell. But crops such as bulbs can be lifted and dried off, and you still have the soil. In any case, at the end of a year, remove any leftover used soil and pile it outside to aerate and revitalize for some months. Then it can be in­corporated again into potting mixtures.

Mixing Soil

Unless you buy or borrow a small cement mixer or similar type of heavy-duty churn, you will have to rely on your own strong arm to mix the soil. I have found a 16-quart aluminum canning kettle a good "mixing bowl." In this I mingle the extra in­gredients (charcoal, sponge rock, and such) with the basic soil mixture. If the mixture is dry, I add enough water so that it will adhere when I pinch a little of it between thumb and forefinger.

Break up large lumps of soil and peatmoss—but for most potting purposes you need not sift the mixture through a screen. However, seedlings and some cuttings do better in screened or milled material.

Soil Mixtures—To Buy or Sell

Of course, you can purchase a ready-made mixture from a large greenhouse, but this should be used only as a starter or in an emergency. Such standard or all-purpose potting soils will not be right for everything you grow. As you learn to mix soils, you may find them an added source of income. You can buy plastic bags in which to sell your own all-purpose mixture to customers. If it is sterilized, it will bring a higher price.

26.  For  a  busy  grower  a  well-organized,  professionally  efficient work room is more than a convenience, it's a necessity. This neat layout indi­cates that Dr. A. J.  Irving of New York holds a good work room in high regard.  (Photograph by Roche)

Sterilization of Soil

All soil should be sterilized before use. In large greenhouses this is usually done by steam, which is too costly for the small grower. But there are good sterilizing chemicals available. I like Fumi-Soil capsules. Place soil in a metal-lined bin, such as a clean garbage can, and add one capsule to each square foot of soil. If this is dry, moisten it a little. When the last layer of soil is placed, cover the container for 10 to 14 days. Then dump the soil out to aerate it before use. Follow package directions faithfully.

For soil in a bench, formaldehyde is a good sterilizer. Use one quart of 40 per cent formaldehyde to 12 gallons of water to cover about 4 square yards. Do not plant in the soil for about a week.

A few growers sterilize by the slow and rather clumsy method of baking soil in the oven for about 1 hour at 180 degrees F. This is not entirely reliable.

Storing Soil

If you must store potting soil in an unheated building, let it stand in a warm room at least 24 hours before use. Avoid fresh manure, it will burn tender plant roots.

POTS—SIZES AND KINDS

Regular clay pots are as deep as they are wide at the top. There are also three-quarter pots, called azalea pots, and bulb "pans." These are not really pans but simply pots which are about half as deep as they are wide. Pans are just right for rooting cuttings and forcing bulbs. The orchid pot has holes spaced all around the sides for extra drainage.

Some gardeners prefer plastic pots. They come in various shapes and sizes and can be time-savers for an experienced person who understands watering and the needs of plants. The plastic pots are lightweight, attractive, easier to clean than clay pots, and more retentive of moisture. Most commercial growers, nevertheless, still use clay pots for growing, reserving the plas­tics for shipping. They maintain that a clay pot is ideal because it is porous. Roots need to grow out and around the inside of the pot, and require water, nutrients, and air, which they receive more effectively in clay. Feel a clay pot filled with moistened soil and you will note that it is 10 to 15 degrees cooler than a plastic pot of soil. And that's a healthy condition for roots.

If you have old pots, scrub them well before use. I add 6 tablespoonsful of Carco-X to the boiler of water in which I wash pots. This antiseptic, which contains some tar, removes soluble salts and algae, and is not hard on hands. Never store plastic pots outdoors, as sudden temperature changes often cause them to crack.

If you live in Arizona, New Mexico, Texas, or other areas where summer heat produces excessive evaporation, you may save work by using plastic pots. However, crusts or chemical concentrates (resulting from fertilizing) may form and neces­sitate frequent repotting or scraping away from top soil.

HOW TO POT YOUR PLANTS

Correct potting and timely transplanting mean extra profits. You'll save time and effort if you first assemble pots, drainage material (pottery chips), soil, and plants on your potting bench. Use only clean pots. If you have new clay pots, soak them in water for several hours prior to potting so they will not draw moisture from the soil. New plastic pots need no washing.

Save broken pots and use the pieces ("crocks") for drainage material.

Repotting

When repotting plants that have outgrown containers, shift them to pots one or at most two sizes larger. Place an arched piece of crock over the drainage hole. For a 4-inch pot, add about a % inch layer of gravel or tiny crock chips. For smaller pots, decrease the amount of drainage material; increase it for larger pots.

To remove a plant from a pot, turn it upside down. Rest it on your left hand, with your finger tips straddling the plant's stem and supporting the soil. Use your right hand to hold the in­verted pot steady. Rap the pot edge against a table or bench and let the plant slip out of the pot. Before repotting, remove old drainage material which may cling to the bottom of the root ball. If this seems hard, with your hands or a stick remove some of the old soil before replanting.

Put a small amount of soil above the drainage material in the new pot, place the plant, and fill in the space around the root ball with fresh soil. Leave at least ¼ inch of space between pot rim and soil level in small pots, up to 1 inch of space in larger pots, so plants can receive enough water at one time. Finish by rapping the bottom of the pot on the bench to firm the soil. If you are transplanting large plants, mature amaryllis or philodendron, center the plant above the drainage material, fill in the sides with soil, and tamp it as you fill. Do this with your fingers or a rounded stick.

How to Pot Cuttings

Stem cuttings are sometimes rooted and grown on in the same soil medium, but more often they are rooted first in flats of sand or sphagnum and then moved into pots of soil. Cuttings are taken either just below a node or between two nodes (those little swellings on the stems) depending on the type of plant. The length of the cutting, too, is variable.

In most cases, you can hasten root growth by treating the base of the cutting with a hormone, Hormodin or Rootone. In­sert the cutting about 1 inch into sand, vermiculite, or peat­moss. Firm the rooting medium around the cutting and water it. Speed root formation by applying gentle bottom heat—about 70 to 72 degrees. When good root growth has formed (in 4 to 6 weeks, depending on type of plant), transplant the cuttings into 2- or 3-inch pots or plant bands or to larger flats, spacing the plants about 2 inches apart.

Use pots or bands large enough to accommodate roots with­out having them touch the sides. Transplant to larger pots as plants grow. With rooted cuttings of plants like coleus and geranium fill the pots or bands % full of soil. Place the rooted cutting on the soil bed and fill in to bring the soil level to within % inch of the pot rim (for watering space).

Firm the soil, but do not pack it so hard you exclude air from roots. After planting, give the cuttings a misting or sprinkling to settle the soil. Harden them in a cool part of the greenhouse for a few days. Growth will be speeded if you place a sheet of transparent plastic over the new plantings. If there is too much moisture, droplets will cling to the inside of the plastic cover; lift it for an hour or two to admit air and help prevent mildew.

Potting Up Seedlings

The first seedling leaves (cotyledons) pushing above the sand or soil are not the true leaves, which generally will be of rougher texture. When seedlings have 2 or 4 good leaves, it is time to transplant to larger flats, or to "individualize" by planting singly in plant bands, 1-inch clay pots, or prepared con­tainers, Ferto-Pots, Jiffy Pots, or Peat-Pots

27.  Another view of Dr.  Irving's tool house-potting shed-work room. Since time  is  money,  whatever you spend in setting up handy tool racks, portable storage cans and other time and money-saving features will be repaid richly and frequently.  (Photograph by Roche)

Make this first shift into soil screened through ¼-inch wire mesh. If you are using plant bands, place the bands in a flat. Fill with the screened soil and, with a pointed stick (or dibble) make planting holes. Commercial growers press a board with dibbles spaced on it into the soil to make several planting holes at once.

Insert the rooted seedlings into the planting holes and firm the soil with thumb or dibble. Water the seedlings and place them in a shaded place for a day or two to help them recover from the shock of transplanting.

Potting Plantlets

Plantlets which form on leaf cuttings of African violets and similar plants have stronger root systems than seedlings and are easier to handle. This applies also to plants formed on the split veins or wedges of rex begonia or gloxinia leaves.

When the plantlets show four or more leaves, lift the original leaf cutting from the soil and carefully cut off the tiny plants. Set them in individual "thumb" (1¼-inch) or 2-inch pots of the recommended growing soil and firm it around them. Moisten with a fine spray and set the plants out of bright light for a couple of days to help them become established. Speaking of thumb pots, use them with care. They dry out very quickly and are easily tipped over if not massed together.

Plantlets forming on the split veins of gloxinia leaves form tiny tubers. Separate plantlets and tubers from the leaf and pot them the same as other small plants.

Many profit-making plants will be rapid growers requiring shifts to larger pots. Shift to pots but one size larger. You save no time by placing plants in pots too large for their root balls. Instead, the fine roots may suffocate due to an excess of water in the soil. Potted correctly, plants can use all the water you give them. Water large plants thoroughly before shifting them. Within an hour or two the water should have drained suffi­ciently for the plant to slip easily out of the pot.

Drainage

Many growers omit drainage material, but I find it is good insurance against rot from over watering. Before potting, place a piece of broken flower pot, curved side up, over the drainage hole of small pots. Medium-sized pots (3 to 5 inches) require several pieces. Flats and bulb pans need a 1-inch layer of pot chips or pebbles, so water can quickly enter soil (with bottom watering) and also so excess water will drain quickly away. Obviously you can make use of plenty of broken pots. Toss them into a container and save them for potting.

In addition to clay and plastic pots, you will be using flats extensively. They are essential for large quantities of seedlings, for starting tender bulbs, and so forth—all of which is covered in succeeding chapters.

Potting and Dividing Older Plants

When you are potting up established plants, remember that they can stand having soil well firmed with your thumb; but do not pack soil so tight as to exclude air. Leave at least 1/2inch of space between soil and pot rim in pots up to 5 inches; at least 1 inch of space in larger pots. Filling up the pot completely with soil will make a one-shot job of watering impossible.

Occasionally you may buy a large specimen of a choice plant, intending to propagate it by breaking it apart and repotting the pieces. If there are several plants in the pot, knock them out. With your thumbs, separate the plant into as many rooted pieces as possible. If the plant still appears to have several crowns, you must cut it apart with a sharp knife. The sections with roots can be potted up in regular potting soil; the un-rooted ones must be stuck in sand or other media to root before potting. As growth on most plants is more rapid in spring, older plants should be repotted if possible shortly before the surge of new growth at this time.

Potting up Seedlings

Potting up seedlings is a little more work. Their first shift may be into community pots or, in the case of tender house plants, into thumb pots. When repotting these seedlings, avoid too much pressure on the roots; being very tender, they snap under a heavy touch. After potting, tap the pot on a hard surface to firm the soil.

Watering Newly Potted Plants

Finally, moisten the soil with a mist. If your hose lacks a mist attachment, place your thumb over part of the hose opening, and turn on the water at low force; it will come out in sprinkles. Or use a sprinkling can to finish the watering. When the plants are potted, set them where they will be out of full sun. Leave them in the shade for at least 24 hours. If they must be re­turned directly to the sunny benches, cover them with a sheet of newspaper laid on lightly—just as we sometimes protect new plantings outdoors.

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