The basic methods of simple plant propagation are easy to master, require very little in the way of tools or equipment, and provide an inexpensive way for gardeners to increase their stock of plants1
The three methods of propagating plants, practised by home gardeners since before the dawn of television horticulture experts, are seed, cuttings, and division.
Propagating plants from seed is essentially nurturing baby plants, the genetic offspring of at least one parent plant. There are several advantages to propagating plants from seed:
It is a relatively cheap way of producing lots of new plants.
It is a good way of acquiring hard-to-find, exotic plants from far away places.
It is a convenient way to share the bounty of your garden with friends.
The disadvantages are:
It takes longer to produce mature plants from seed than it does from cuttings or divisions.
Propagation from seed takes a lot of care and attention, and, in many cases, a good deal of experience and knowledge.
New plants from seed won't necessarily come true to type. They will be genetically distinct from their parent(s), so you may not end up with what you hoped for.
Those who are fortunate enough to own a greenhouse have an advantage over the rest of us. But perfectly satisfactory results can be attained on a table top in a sunny window. Or, to save a little space, shelves could be attached directly to window frames. Seeds can also be grown under artificial lights. Specialty lights are recommended for this, because ordinary incandescent bulbs produce a very limited spectrum of light and they get very hot.
The basic requirements for growing plants from seed are moisture and a sterile (clean) medium. Soil from the garden is not a good choice, because it contains an amazing amount of fungi and microscopic creatures, which can be harmful to your seedlings. And, although it is possible to kill many of the natives in the oven or the microwave, it is time-consuming and smelly to do so. It's a much safer bet to buy some potting soil or a commercial peat-based product. The latter, called soilless mixes, are favoured by many professional growers, because they are light, have a high water-holding capacity, and do not compact in containers after repeated irrigation. They are usually a blend of milled sphagnum peat, vermiculite, and perlite.
Whatever medium is used, it should be sieved to remove big clumps and to allow good contact with the roots of developing seedlings. When sowing very small seeds, it is a good idea to add a top layer of soil, which has passed through a fine seive, so that the surface layer is almost powdery.
One of the wonderful things about home gardening is the many forms of eccentric behaviour that gardeners are expected to engage in. And one of the most wonderful of these is the collection of wildly eccentric containers for growing baby plants in.
Seeds can be started in almost anything, as long as there is some provision for water to drain out. Having said that, obviously some containers are better than others. The best are simple trays, capable of holding about 5cm of soil. The advantage that trays have over old wellington boots is that they allow humidity to be controlled by laying a pane of glass on top, which can be propped up to varying degrees for ventilation.
- Plant pots (shallow bulb pans)
- Egg cartons
- Old baking trays
- Margerine containers
... and so on. Use your imagination.
Seeds can also be started by sealing them, with a small amount of moist soil, in glass jars. This offers the advantage of maintaining a uniformly high level of humidity. The disadvantage, of course, is that it is tricky to prick out the seedlings, once they begin to grow.
The vast majority of seeds will germinate if they are given a lttle warmth, a little light, and a little moisture. There are some, though, that will not. Nature tries to ensure the highest success rate for her own garden by designing seeds with built-in safeguards against premature and inopportune germination. She does this by programming the seeds with a period of dormancy. This is to prevent seeds from germinating at the wrong time of the year, and to allow them to be transported a respectable distance from their parent.
To coax difficult seeds to germinate gardeners must replicate the passage of time and accelerate the natural rate of wear and tear:
Stratification - This is a technique used to trick seeds into breaking their dormancy by simulating the passage of the seasons. Seeds are chilled for a specific period (depending on their type) at a specific temperature. Sometimes seeds require a second period of chilling to break their double dormancy. Some seeds require a long soak in water, or even acid, in order to break their dormancy.
Scarification - This technique accelerates the rate of abrasion that thick-coated seeds undergo in nature. Seed coats are cut or filed to speed up germination.
Pricking out is not rude. There is no need to snicker or look apologetic. This is the operation used to transfer young plants from seed trays into plant pots or plastic cells. It is a task usually accomplished with the aid of a dibble, a pencil, or even a chopstick. The ideal time for this is when the first true leaves develop. The trick is to treat the seedling as gently as possible. Handle the young plant by a leaf, so that the fragile stems aren't bruised. Work quickly; it only takes a few seconds for the tiny roots to dry out.
This is a truly awesome spectacle when it is performed by an old gardener with hands like gnarled roots, who performs this delicate task at an impossible pace for hours at a time, without showing any sign of tiring. To a novice - or someone pressed into service - this can be excructiating work.
A lot of fuss and bother can be avoided if you elect to sow your seeds directly in the garden. The disadvantage, of course, is that you have to wait for warm weather, which may limit the crops available to you.
Some seed can be sown in cold soil in very early Spring, but most should be sown in warm soil. Some perennial plants may need to have their seed sown in the Autumn, in order to break their dormancy in the following Spring.
Soil in the seed bed should be a very fine tilthe, to ensure a good soil contact with the seed. Larger seeds can be sown in rills, or in individual holes poked into the soil with a dibble. Very fine seeds are best mixed with an inert medium, such as sand or fine, clean soil, and then broadcast over the bed.
Gardeners should be prepared to lose some seed to birds and rodents, as well as to wind and rain.
New plants produced from cuttings differ from those grown from seed in that they are genetic replicas of a single parent plant. This is important if you want to propagate specific characteristics. Breeding plants in the quest for improvement can be a long and complex process2. Once a plant is found which fits the bill, it is propagated vegetatively (by cuttings); and the resulting progeny are referred to as cultivars of the parent plant.
Softwood cuttings are taken from the immature tips of new growth. These should bend easily, without snapping.
Take a cutting about two inches long with a sharp knife or a razor blade. It should have at least two sets of leaves.
Cut off the bottom leaves, and trim the cutting just below the bottom leaf node.
Trim the remaining top leaves by about two thirds, to reduce water loss.
Shave off a thin slice at the base of the cutting to expose the green cambium layer.
Dip the base of the cutting into softwood rooting hormone powder, and tap off the excess.
Plant the cutting in a clean, coarse growing medium, and cover to conserve moisture.
Some plants will produce new roots from the area of the cutting between the leaf nodes. These are referred to as internodal cuttings.
Semi-hardwood cuttings are usually taken from lateral growth. They are taken from tissue that is just beginning to mature. Semi-hardwood cuttings from most shrubs and trees, growing outdoors, are taken in the mid-Summer. Often a small slip from the main branch, a heel, is taken with the cutting.
Hardwood cuttings are taken from mature wood, often with a heel. They are usually taken at the end of the growing season, in the late Autumn. They can be planted straight away, but often they are tied in bundles and buried in moist sand or soil, left over the Winter, and planted in the following Spring. To make it easier to tell which end is which, the cut at the base is usually made at an angle.
All Willows are ridiculously easy to grow from cuttings. Experience has shown that soaking hardwood cuttings of more difficult plants in warm water with willow twigs will increase the success rate.
It is also possible to produce cuttings from roots or even leaves. Many perennial herbs are propagated by root cuttings. Many house plants, such as African Violets (Saintpaulia), are usually propagated from leaf cuttings, which are laid on the surface of the soil. The main veins are often incised to encourage rooting.
Layering is a method used to encourage new roots to grow from the stem of a plant. The new plant is then simply cut from the old one, just below the new roots. This usually means simply bending the stem of a plant down to the ground, making a cut through about two thirds of its diameter, and covering it with soil. Sometimes the wound is held open with a tiny stick, and rooting hormone may be used. Air Layering is essentially the same process, except that the soil is contained in dark plastic, which is bound tightly around the stem.
Propagating by division is by far the simplest method of increasing your stock of plants. Simply put, it is taking a few big things and turning them into lots of smaller things. This is the most popular way to increase herbaceous perennials.
Mature plants are dug up in the Autumn or early Spring and either pulled or cut apart. The best candidates for this treatment are perennials which naturally form clumps, and have fibrous root systems, such as Asters, or Daylillies (Hemerocallis). These can be divided effortlessly by pushing two garden forks through the clumps, back to back, and then prying the forks apart.
It is possible to divide herbaceous pæonies. But they can be a little tricky, because their thick, fleshy roots are quite brittle. A clump of pæony roots can look like the arthritic hands of an old gardener tying a bowtie. The trick is to remove as much soil as possible with a hose, and then let the plants wilt slightly in a shady place. This will cause the roots to soften enough that it is possible to untangle them without a lot of breakage. Each new section should have about five 'eyes'. They should be replanted just deep enough to cover the 'eyes', otherwise you may have a long wait before you see any flowers.