PROPAGATION: BEG A CUTTING

Rather than blowing the budget on a flat of coleus, buy one of everything you like and grow a dozen more of each. Take advantage of spring growth spurts to root cuttings of tropicals and tender perennials that will mature quickly in summer’s heat and bloom with their parents. Taking cuttings of fresh growth again in late summer and fall is the best way to overwinter plants that grow too large to easily bring inside. Those original cuttings might stretch and become gangly through the winter but they will produce new growth in early spring ripe for taking a fresh round of cuttings to plant out in the garden.

The first step is to choose a rooting medium. Most of us have successfully rooted coleus and begonia cuttings in small glasses of water set on the windowsill. But water has a couple of drawbacks. Some plants will rot before they root. And because water doesn’t offer new roots any resistance, rooted cuttings may take a while to adjust to growing in soil.

The ideal rooting medium will retain moisture but still drain well. It should also be coarse enough for oxygen to reach the buried stem, sterile, low in fertility, and supportive enough to keep the cuttings from falling over. The best options, used singly or in combination, are perlite (a crispy white volcanic glass capable of holding ten times its weight in water), and vermiculite (an expanded mica that also holds a lot of water without becoming waterlogged), both of which are lightweight, perfect support for the delicate root systems of most perennials. Coarse sand, peat moss, or soilless potting mix may also be used but are less ideal. (Sand is dense, better suited for shrub and tree cuttings, and it can be difficult to regulate the moisture content in peat moss and potting soil.)

Professional propagators use a shaded cutting bench filled with their preferred medium and rigged with bottom heat and a system that automatically mists the cuttings when the medium begins to go dry. The rest of us can use a homemade Forsythe pot, which doesn’t require complicated plumbing and works just as well. With this method, one container (preferably plastic) holds the medium and cuttings as they root, while a smaller porous terracotta pot sits in the center of the first container and gradually and evenly seeps water to the cuttings. A clear plastic bag tented over the top keeps the humidity level high, which helps prevent wilting.

Taking tip cuttings

In most plants, the versatile cells that wait for hormonal direction before growing into whatever the plant needs—be it shoots, roots, or leaves—reside in leaf nodes along the stem, at the very tips of a plant’s freshest growth. Convince those cells to make roots by exposing and burying them.

Choosing the tips

Early morning, before the leaves have transpired the day’s water away, look for new growth and critique it like Goldilocks. If the stem is floppy and weak, it’s too soft. If it’s stiff and woody, it’s too hard. If it’s flexible and green, it’s just right. Try to find tips that haven’t yet produced a flower bud. That is especially difficult in late summer, when plants are extra busy producing flowers from every tip. Look for non-flowering new growth at the base of the plant or from lower leaf axils.

If a plant hasn’t produced cutting-worthy growth by the start of the school season, try pruning a few of the plant’s stems by half (or to the ground) to trigger a fresh flush that will be ready for cutting in two to four weeks. Otherwise settle for tips with the smallest undeveloped buds. Remove growing tips below at least two sets of leaves (three to be safe). If you can’t immediately prepare the cuttings for sticking in rooting medium, place them in a jar of water or wrap them in a wet paper towel inside a plastic baggie to prevent wilting.

MAKE A FORSYTHE POT

MATERIALS

1 clean gallon-sized plastic nursery pot and saucer

1 sheet of paper towel or window screen (sized to cover the drainage holes of the plastic pot)

Perlite or vermiculite

1 unglazed terracotta pot (4-inch diameter) with rubber stopper or cork

STEPS

1. Cover the drainage holes of the plastic pot with the paper towel or window screen. Then fill the pot almost to the top with the perlite or vermiculite medium.

2. Plug the drainage hole of the terracotta pot with the stopper or cork. Place the terracotta pot into the center of the medium and push it down so that it sits flush with the top of the plastic pot.

3. Run water through the medium and then fill the terracotta reservoir with water. The Forsythe pot is now ready for your tip or leaf cuttings.

A Forsythe pot with an assortment of cuttings taking root.

Prepping the tips

To prepare cuttings, you will need to make a few cuts with a clean sharp knife, scalpel, or razor blade. Make the first cut ¼ to ½ inch below the second or third set of leaves, then cut the lowest set of leaves off at the stem, taking care to not damage the stem. New roots will form from these cells at the leaf node and the stem end. Cut the remaining leaves in half to keep the cutting from transpiring more water than the stem can draw, and remove any flower buds to help divert energy to root production instead.

Some plants are sufficiently hormonal on their own but giving them a little extra incentive with rooting hormone won’t hurt. You can purchase rooting hormone in powdered form, with and without fungicide—choose the one with—or as a gel. Dip the end of the stem in rooting hormone and tap off the excess. (Rather than dipping straight into the container, fill a small dish as you need it—this will prevent possible contamination.)

You can also make your own rooting hormone using willow (Salix) twigs, which happen to be excessively hormonal and full of infection-fighting salicylic acid. The process is simple. Cut first-year growth from any willow, remove the leaves, and recut the twigs into 1-inch sections. Place them in a bowl, cover with boiling water, and let them stand overnight. In the morning, strain out the twigs and refrigerate the water, which should remain useful for up to two months. Let your cuttings stand in the willow water for a few hours before sticking them in the medium.

Finding a decent tip for cutting on a blue anise sage (Salvia guaranitica).

An African blue basil (Ocimum ‘African Blue’) tip cutting before and after preparing it for sticking.

Ready for rooting

Use a pencil or chopstick as a dibble to poke holes in the rooting medium of the Forsythe pot. (The holes should be just deep and wide enough to insert your cuttings.) The bottom of the cutting should contact the medium with the cut leaf node under the surface. Snug the cuttings in so they stand upright and allow for airspace between them. Cover the pot with a clear plastic bag, supporting the bag with a few pencils or chopsticks to keep it from collapsing onto the cuttings.

Place the pot in a warm, bright spot out of direct sunlight. Check periodically to see if the terracotta pot needs to be refilled with water; at the same time, tug the cuttings gently to determine if they have rooted. If they resist, they’re ready. If they still feel loose, they need more time (two to four weeks should do the trick). Once cuttings have rooted, scoop them out gently and pot them up—there’s no need to remove any medium that stays attached to the roots. When you are finished, top up your Forsythe pot and start all over again. Note that vermiculite breaks down much faster than perlite so it may need to be replaced more often.

A Forsythe pot full of cuttings and tented with a plastic bag to keep the moisture level high.

Taking leaf cuttings

Certain frost-tender keepers (begonias, echeveria, graptopetalum, and kalanchoe, for example) may be propagated from their leaves as well as stems. Leaf cuttings not only root, they generate a plantlet, a whole new tiny plant.

To propagate any plant whose leaves are attached by a petiole (fleshy stem): cut off a leaf, keeping an inch or so of its petiole, then dip the end in rooting hormone, shake off the excess, and stick the leaf upright in the rooting medium. If the leaf is large, cut off the top half to reduce transpiration. Leaf cuttings may take a month or two to form roots and a plantlet at the base of the petiole.

To propagate the leaves of succulents, snap them off at the stem and lay them on their side or stand them upright in the soil or medium. Plantlets will form, usually within a month, from the broken end. Dusting with rooting hormone powder is optional.

A fallen leaf from Graptoveria ‘Fred Ives’ (a cross of echeveria and graptopetalum) forming roots and a plantlet.