The plants you grow may be for your own benefit, for sale, or for the worthy cause of propagating wild flowers to put back in their natural habitats to help save them from extinction. Whatever your aims, you might as well learn about some of the methods that have proven most successful. The common method, of course, is planting seeds, which are the result of sexual reproduction in all cone-bearing and flowering plants. But you can also learn to grow ferns from spores. Here is the beginner’s guide to plant propagation.
They and many seed-bearing plants can also be propagated asexually, or vegetative, by those other methods. For example, many fruit trees, house plants, and hybrid ornamentals are grown from cuttings and graft unions in order to keep the strain pure and to get daughter plants which will definitely breed true to the parent plant.
Asexual means are often much quicker, too. I am glad that I have learned about the many plant propagation practices that have been developed over the years.
Things to Know and Things to Have
For the early steps in propagating you will need certain materials and equipment that have been found successful over the years for various methods and various kinds of plants by gardeners and professional breeders. Even so, your options are many.
Many starting and potting mixtures have succeeded, so you might as well try out what appeals to you and what is possible with the supplies and equipment you find easiest to get. But there are important principles to keep in mind when you are experimenting.
For cuttings, the starting medium should be clean, or sterile, sharp, and rather scratchy, with small enough particles so that the mixture can be packed down to come in contact with the stem you insert. It must be able to hold water and to circulate some air. Make sure at least one ingredient is included which can also absorb water, but there should not be too much this because it might block good drainage and the entrance of enough air for the young roots which will come from the cutting in time.
A soggy medium for stems like those of geraniums will encourage black rot and ruin the cuttings. The scratchiness is desirable so that there will be extra little wounds made along the stem, all of which raise your chances of getting the response that will cause good rooting.
If, however, you choose a mixture that is not very scratchy to start your cuttings, have more sand on hand to line the hole where you insert the cutting so it can be scratched when you put it in. Several recipes for starting or rooting mixtures are given in the next chapter, but one common proportion of materials used by many experts is a 1-1-1 combination of coarse builder’s sand, to help drainage and to be scratchy; vermiculite or perlite; and milled sphagnum moss or peat moss, to support the stems and to hold water.
Starting Mixtures for Cuttings and Seeds
You can put the moss through a sieve to shred it; and after you do this, moisten it slowly, let it rest for several hours, and then press it down before measuring it. Sometimes you can layer such a mixture putting the sand in first, the vermiculite or perlite next, and sphagnum moss on top; also put sand in the holes made, as suggested above.
Make the same sort of sterile mixture for starting seeds indoors, though of course the value of the sand for seeds is not scratchiness but good drainage. A starting mixture for the seeds or cuttings of acid-loving plants is often made from 3 parts of peat moss and 2 parts of sand.
When you use a mixture like this, I’d recommend sterilizing the sand, for acid-loving plants are especially susceptible to pathogens, especially strange fungi to which they are not accustomed. (Acid peat moss is already sterile.)
In the old days, leaf mold was often used for acid-loving plants, in combination with loam, peat moss, and a little sand. Then clean, sterile sand was also sprinkled on top of the flat after the cuttings were put in, to keep the surface sterile. Now vermiculite is often used instead, though sphagnum moss is also excellent because of its special qualities of acid and antibiotic sterility.
(To make a supply of pure leaf mold for this mixture, rake oak, beech, and other leaves into a heap inside a board frame, with good spaces between the boards to provide air. Water and tamp down the leaves as you add layers. Do not add weeds, green stuff, or twigs, which will invite fungi to come in instead of the bacteria you want to work on the leaves. Also never add manure, nitrogen meals, lime, or any leaves taken from tarred roads. Ripen the leaves for two years and then use in all mixtures calling for leaf mold. You can also substitute leaf mold for peat moss in all combinations except those calling specifically for acid peat.)
Potting Soils for Rooted Cuttings and Seedlings
Once started, rooted cuttings and seedlings grow fast, and nutrients are soon needed for the roots to draw on. Unless you have provided in some way for nutrients to be added to the starting mixture, you will need to move the young plants to a regular potting soil with loam in it. One method for including soil in the starting mixture is to fill your flat first with a layer of broken crockery or pebbles and gravel.
Then spread some nylon stockings over this to hold up the next layer of soil, on top of which you put a starting mixture for rooting or germinating. With this arrangement you still have fairly sterile conditions in the area where the seeds or cuttings are getting established, but you also provide nutritive material the roots can reach down to as soon as they start growing.
These will be new, tender roots, so you must be sure that the soil is loose enough to let them through. You don’t want to start their life in an environment where they have to struggle and be stunted because they cannot get through to what they need.
Peat or compost added to the soil layer will help to encourage the roots to grow. Keep them encouraged, and give light additions of fish emulsion or sea- weed solution or whatever mild organic fertilizer you wish. Setbacks at this early stage from lack of nutrients, water, and air can be very serious.
For best results, sometimes it is wise to make up mixtures of a wide selection of ingredients which can provide for several situations. These blends can very well include manure for extra nitrogen.
Then, as the plants grow larger, enrich the mixture from time to time with bone meal, dried blood, and hoof and horn meal.
The garden loam you might scoop up to put into a potting Pasteurizing Loam mixture may cause trouble, and is not going to be nearly so successful as pasteurized soil. It is imperative to know the difference between pasteurized and sterilized soil, and unfortunately people who give out gardening advice often recommend sterilizing.
Do not do it. Sterilization is usually at a temperature of 250°F and that is high enough to kill all the beneficial organisms you definitely want to have in the soil to help your plants. It is much better to pasteurize, for pasteurization means heating no higher than 180°F. It is useful to know that when you steam soil at 120°F., it will be cleansed of nematodes; and that at 140°F, most plant-pathogenic worms, slugs, and centipedes will go; but that it takes 160 Fahrenheit degrees of heat to rid the soil of all pathogenic bacteria.
At that heat the beneficial bacteria, it is believed, are not harmed, even after the recommended 30 minutes of steaming. Maybe 15 minutes of steaming is enough if you are only working with small amounts. And if you use a pressure cooker at 5 pounds pressure, you can reduce the time to 10 minutes.
The thing to remember is that too much heat is worse than none, for then you run the danger of killing all the living inhabitants needed for antibiotic and biochemical actions, and also of burning the organic matter, making it nearly useless for good soil health and good soil structure. In fact, if you use too much heat on peat moss or sphagnum moss, you might injure the moss and even create substances that can kill beneficial soil organisms. This could ruin the value of the humus.
Pasteurize the soil, therefore, before you add either kind of moss or compost. The compost or compost tea you add is likely to be free of pathogens. That’s because the heat of a well-made compost heap will disinfect the materials, for the temperature in such a heap goes up to 145°F or so.
And remember that sphagnum moss is already sterile, and so are vermiculite (which is expanded mica) and perlite (exploded volcanic ash). Potting mixtures you buy at the store are also sterile. The sand you use, of course, can be heated to any degree you wish because it is inert and no harm will be done.
Testing for Humus
If you are in doubt about the organic matter or humus in the soil you plan to use in your potting mixture, put some soil in a bottle of water and let it settle. The minerals will go to the bottom, and if there is no perceptible layer of lighter weight organic particles on top of the mineral layer, you know that you will want to add some good compost, pure leaf mold, peat, sphagnum moss, or whatever is needed to amend the mixture.
Keep Good Loam on Hand
A propagator who plans to make a lot of cuttings or to plant a lot of seeds indoors (or in a greenhouse) would do well to keep a supply of top-quality loam on hand, ready to steam for use. Keep the supply fruitful and productive by adding plenty of compost and nutrients as needed: examples are bone meal, dolomitic limestone, greensand, granite dust, and rock phosphate.
Keep improving the mixture over the years. You will then have a supply of the best sort of medium when you add it to the sand, moss, and vermiculite needed for propagation.
The benefits of a good loam in a good mixture include a more even temperature in the mixture, an increased capacity to hold the soil solution and its nutrients, a moderated pH that is not too acid or too alkaline, a better habitat for the soil microorganisms you need, and a closer affinity between the tiny new roots and root hairs and the soil particles and nutrients made available by the microorganisms that cluster in great numbers around new young roots.
Loam also provides enough air to promote the rapid oxidation characteristic of the very early growth of your new plant. This good soil, then, will have approximately 25 percent air, 25 percent water, 5 to 15 percent organic matter, and 35 to 45 percent mineral matter in it.
The Right Environment for Propagation
Water, both in the mixture and in the air, is essential. Seeds cannot swell and grow without a good supply. Cuttings and grafts cannot “take” without it, for they then wilt and shrivel. To keep the air and medium moist, shade is often needed.
In nature a few leaves, twigs, pebbles, or clods of earth are often enough to shade tiny seedlings, but in flats or out in the garden, artificial shade is frequently needed for both seedlings and cuttings.
Indoors it is easy enough to move flats into the shade or pull the curtains closed. Outdoors you can stick in small branches of brush on the sunny side of the plants or put on hot caps or homemade caps of newspaper.
Whether you’re using pots, flats, or the special propagation devices, you can put plastic or glass coverings over cuttings inserted in the rooting medium. If you use plastic, it should be polyethylene or polypropylene. Polyethylene and polypropylene are permeable to oxygen; all the others are not.
But plants need carbon dioxide as well as oxygen. Mist-sprays are often the best method to use to keep cuttings well-provided with a moist environment. This is a good method to use when the particular plant you are propagating needs a good deal of light and you’d be unwise to use shade.
Once the roots emerge, you need microorganisms to aid in Helpful Microorganisms the biochemical processes of supplying nutrients to the plants. Luckily you do not have to work at this because, unless you have killed the beneficial bacteria and fungi with overheating, they arrive anyway. In fact, there will be 3 to 50 times as many of these microorganisms near the roots as there are in other parts of the soil.
Because the soil in the garden also includes nematodes and other such pests, you may need to include marigolds in your garden environment once you plant out your new seedlings or cuttings; or you can provide manure fertilizers, which nematodes are said to avoid.