Like all creatures on planet Earth, our ornamental plants just want to reproduce. And they have a variety of ways to do it, ways we can take advantage of in order to get many more of them at no cost except for a little pleasant time and effort in the garden.
February and March are the right months in our part of the world to propagate ornamentals. As the weather begins to warm up, plants with root systems that persist from year to year, such as perennials, roses, shrubs and many others, start producing hormones that stimulate growth of both roots and vegetative foliage. It is when plant tissue is flush with growth hormones that we have the best chance of success when propagating.
Plants produce new plants by making seed, by producing new growing points (crowns), by extending underground roots that produce new top growth at intervals and by making special structures in plants of the lily family (bulbils). We humans add other techniques that plants don’t often or never do by themselves: taking and rooting stem cuttings; cutting segments of fleshy roots and replanting them; and layering and taking apart lily bulbs into their single scales and replanting these.
Let’s take a look at these techniques one by one.
Seed — Only open-pollinated plants produce seed that grows into the same kind of plants. Hybrids — that is, crosses between subspecies with slightly different characteristics — will produce seed that shows whatever variations were in the parents’ DNA. In other words, if you plant hybrid seed, the resulting plant may not be anything like the hybrid it came from. Annuals like Love-in-a-Mist (Nigella damascena) are more likely to be open-pollinated than the seed of perennials. If you want to save seed of a favorite flower or herb, just make sure that it’s not a hybrid. If the botanical name is known, and there’s an X in front of the species name (for instance, Dianthus x allwoodii), that X tells you it’s a hybrid.
Division — Many flowering perennials evolved in temperate zones, where the roots persist in the soil while winter kills back the top growth. Plant a perennial with one crown — a crown is the growing point from which the stems arise — and the following spring you may find that the plant has made two or three smaller extra crowns over the past growing season. You can dig up the whole plant and gently separate these crowns, and each will have its own set of roots. If the plant hasn’t been divided in years, you can hack between the crowns with a Japanese saw.
Now trim back any long, trailing roots, trim old stems back to within an inch of the crown, and replant so the crown is just at soil level. Water the crowns well. You will have many plants where you had one before.
Extending underground roots — Think of bamboo, or just about any other invasive plant that spreads by underground roots. Plants need no help from us in making babies this way. Our job is more like keeping this technique from overrunning the garden.
Stem cuttings — When a semi-woody plant like a rose or a flowering shrub is pushing new buds, cut off about 8 to 10 inches of the growing tip of a stem or branch, dip the cut end in root hormone (available at any garden center or online), plant 4 to 6 inches deep in good soil or in pots, water well, and cover with clear plastic bags to keep the air humid.