Hampton Gardener: Go forth and propagate

You’re at a friend’s house or on a garden tour and as you’re walking through the garden your eye is caught by the most magnificent coleus you’ve ever seen. The colors are unlike any combination you can recall and the sword-like foliage is completely unfamiliar. You’ve got to have one for next year’s garden, but no one knows where it came from let alone its name. There’s also that wonderful hibiscus you saw in another garden and while you know it’s a hardy perennial you’ve never seen the pink flowers with red striations and faint stripes and blotches. How in the world can you find out where to get one of these?

Or maybe you’re walking down the beach and just on the water side of the dunes you notice a wonderful grey foliage plant with tiny yellow flowers that makes a wonderful ground cover in the sand. That’s right, it’s growing in the sand. You get home and search your books on seashore plants to find that it’s beach wormwood (

Aretemisia stelleriana,

) but only one mail order nursery out in New Mexico is offering it and, according to its website, the variety is unavailable.

What’s a gardener to do?

Propagate!

The process is called asexual propagation (as opposed to sexual propagation where seed is produced) and in the case of all of the above examples, and hundreds of others, the method is to take what we call soft wood cuttings, strike them in a medium, get them to root and almost like magic you have an identical replication of the plant you want. Yes, it’s the most basic and rudimentary way of cloning and man’s been doing it for centuries. Better yet, you can do it at home at little cost and as your experience level increases you’ll find yourself taking cuttings and growing plants you never dreamed imaginable. But start simple and learn the rules (and tricks).

The cuttings that we’re seeking are generally from annuals and some perennials (though many perennials can be propagated by division) that for various reasons can’t be grown from seed. The cuttings of the annuals need to be taken while the plant is vigorously growing and before cold weather has signaled that it’s time to close down for the season. In addition, the plant should not be flowering or at least the shoot that you’re cutting from should not be flowering. Cuttings from perennials need to be taken early in the season before the stems begin to turn woody and also before flowering begins.

Cuttings are usually taken from the apex or growing tip of the plant. As a rule, the cutting should be 2 to 3 inches long with at least three leaves. If side shoot cuttings are taken, there’s a good chance that the plant from the cutting you’re taking will always grow sideways and while this works for plants in hanging baskets it usually doesn’t work well for plants going into the garden. Remember that plants like our coleus are genetically primed to complete their life cycle in one year or less, so you may have to take cuttings of your cuttings several times in order to have the plants you want for next year’s garden.

Cuttings should be taken on cloudy days; cloudy humid days are perfect as the cuttings will remain turgid and this is critical for success. Wilted cuttings rarely recover and easily rot. Cuttings can also be taken very early in the morning before the sun hits the plant, or at dusk, but never during the day. Have your propagation set up ready to receive your cuttings as soon as you cut them although a few plants such as geraniums can go for several hours before you “strike” them. Striking is the act of putting the cutting into the rooting medium.

In order to root your cuttings you usually need to dip the cutting into a liquid or powdered rooting hormone that stimulates root growth. These preparations come under trade names like Hormonex and Rootone and are available in small foil packets or small plastic jars. Some contain a fungicide that reduces the chances of bacterial and fungal rot in the warm and moist rooting media. There are also liquid hormones that claim to be more successful than the powders. The hormone is applied by dusting or dipping the cutting only on the length of stem that will be struck in the medium. One or two of the bottom leaves are removed, the stem dusted with a fine brush or dipped in the jar or packet. The excess is then shaken off the stem, as only a light coating is necessary.

You can buy domed plastic trays, small propagation houses (about the size of a standard flat or 11 inches by 22 inches) or simply use a plastic bag. In a tray, cell pack or very small pot, add sand, vermiculite, perlite or a propagation mix made of peat moss, perlite and vermiculite. This is your “medium” and it should be lightly moistened, not dripping wet. Never use soil from outdoors as it will contain pathogens that will induce rotting and never use a potting soil that has fertilizer in it as this will burn any roots that try to form. Using a pencil or dibble, make a hole down into the medium to the depth of the cutting that you are striking. Depending on the plant, roots will initiate either where you took the leaf off or where a callous forms at the cut end. Don’t push (you’ll rub off the hormone) but gently put the cutting into the hole and gently firm around the cutting.

Next, take a misting bottle (any spray bottle will do as long as it’s clean and contains only water) and gently mist the foliage of the cutting. Place the dome over the cutting or, if you’re using a pot and a plastic bag, put the pot in the bag and close it (zipping bags work great) making sure the bag doesn’t touch the cuttings. Place the whole setup in a bright area, but not in a place where it gets too hot or where the sun will hit it. The sun will bake your cuttings and since they have no roots yet, they are unable to deal with the water loss caused by the bright light and heat.

For the best results you’ll need a source of bottom heat as the soil temperature should be a constant 68 to 72 degrees. In the summer this can usually be accomplished in a warm spot in the house but at other times of the year we use heating cables, heat mats and other methods.

Now, the trick is patience. Depending on the plant you’ve taken the cutting from, rooting can take from two weeks to months, but your coleus should root in a couple of weeks. Mist the cuttings at least once a day as mist on the foliage reduces transpiration and wilting. The soil should remain moist, but not wet and you should never pull the cutting to see if it’s rooted. Control yourself. In time you’ll learn how long any given plant will take to root at certain times of the year, then you’ll know when to give that testing tug.

Silver leaved or hairy leaved plants such as the beach wormwood should not be misted and you may find that they will root better without the use of a hormone dusting. Plants like this seem to root well in coarse sand and at a higher temperature.

Once your cuttings are setting roots, reduce the humidity by opening the bag over a period of a few days or vent the dome beginning in the morning and evening. Then, when you see that the cutting remains turgid (rigid), the dome can be removed. When well-rooted, transplanting can take place and you can begin light liquid feeding, preferably with an organic material like fish emulsion or another low nutrient organic fertilizer.

In the case of perennials like the hibiscus, rooting will take longer and by the end of the summer you may have a plant with only a dozen or fewer leaves and a very tender root system. If you were to plant this out in the garden at this point the roots would not be hardened enough or mature enough to make it through the winter. Cuttings like this and those from vines like clematis should be overwintered the first winter in a cold frame where temperatures will moderate and not kill the new roots.

The idea with plants like coleus and geraniums is to create “stock” plants that you will grow through the winter making them stocky and lush with terminal growth. This is accomplished through successive pinching or pruning which also forestalls flowering. In late winter, cuttings are again taken and rooted and it’s these cuttings that will be your planting out material for next summer’s garden.

So, go forth and propagate. Beware of plants that may be patented or have copyrights as the commercial propagation of these plants can get you into hot water. For your own personal use at home though, rooting a few cuttings won’t get you into trouble. Keep growing.

Andrew Messinger has been a professional horticulturist for more than 30 years. He divides his time between homes and gardens in Southampton, Westchester and the Catskills. E-mail him at: Andrew@hamptongardener.com. The Hampton Gardener is a registered trademark.