Tips for starting new plants from cuttings

At the awkward stage of development we call puberty, our bodies produce hormones that trigger and enhance our development into adults.

The same thing happens with plants, though on a different timeline and with different results. As the sun strengthens in February in our part of the country (and in March and April elsewhere), plants begin making hormones, which carry messages to their tissues: “Wake up,” “Start growing,” “Produce new roots” and “Leaf out.”

Gardeners can catch plants in February when they are chock-a-block full of hormones stimulating them to grow and use that time to expand plantings for free. If you have favorite plants in your garden, from perennials to flowering and fruiting shrubs and trees, and would like more of them, don’t rush to buy more. Consider propagating the ones you already have.

The front edge of my driveway is lined with three bunches of hardy gloxinia (Incarvillea delavayi), a lovely perennial with scads of pink trumpet-shaped flowers very much at home here in Sonoma County.

Originally, I brought home a rooted cutting in an 8-inch pot and planted it. After a couple years, it grew into a large plant about 18 inches in diameter. So I cut the fibrous root ball into three parts, tripling my stand for the cost of about 10 minutes’ work. Next year, I’ll triple each of those and have a lovely drift of nine hardy gloxinias welcoming us home whenever we park.

How to propagate from root cuttings

Hardy gloxinia is a good example for propagation because you also can take root cuttings and quickly multiply the number of plants.

Start by filling 8-inch plastic pots with four parts potting soil and one part perlite. Gather 4- to 6-inch cuttings from the base of a healthy branch, taking as many as you have pots. Make sure each cutting has at least 1 inch of underground growth with new roots beginning to show. This means the plant hormones are active and working in the root zone.

Bury the cutting to half its length in the pot. The underground portion should be completely covered with soil. Firm the soil to hold the stem upright.

Place the cuttings in their new pots in bright shade, out of the prevailing wind and protected from afternoon sun. Keep the pots moist but not sopping wet for about six to eight weeks, until the cuttings put on significant growth. Then transplant them into your garden beds.

This method works for many perennials with fibrous roots that grow by sending out new shoots from their edges in early spring. If, after several years, you see a perennial’s center has died out leaving a ring of new growth, cut the ring into sections with several crowns (growing points) and replant them in soil refreshed with compost.

Tap-rooted perennials are much tougher to propagate

If you have tap-rooted perennials like Baptisia, butterfly weed (Asclepias species), rattlesnake master (Eryngium) and Amsonia, among others, propagation isn’t as easy. But it is possible.

You’ll need to cut a piece of the taproot on one side that has an eye (like a potato) and a secondary root attached to it, then replant that as deep as it was in its original soil. Keep it well watered. The mother plant also should regrow.

Plant hormones are at work when you propagate woody shrubs and trees by taking stem cuttings. February into early March is the best time to do this because the plant hormones are working hardest then and are concentrating in the tips of shoots. You’ll want to cut the shoots before the buds open.

Cut 6- to 8-inch stem tips with clean, sterilized pruners. Dip the cut end into an inch of root hormone, sold at most garden centers or online. Then bury the cutting several inches deep in a mix of four parts potting soil and one part perlite, in generous 1-quart or larger pots. Water them in. Place four bamboo skewers around the edges of the pots and place a clear plastic supermarket vegetable bag over the skewers, forming a mini greenhouse to hold in moisture.

After the buds burst and the first leaves appear, remove the plastic bag and keep the cuttings moist and in bright shade. Transfer them to a garden nursery bed until the cuttings finish their first year. Then plant them in the garden or landscape in the late fall when the plants are dormant, or in the early spring of the next growing season.

Plant hormones that are your helpers

Three plant hormones are your helpers — and you theirs — when propagating plants in February or March.

Gibberellins break the dormancy of seeds and buds and promote growth. Cytokinins promote cell division of roots and green growing tissues.

Auxins are involved in many plant processes, including turning toward sunlight and apical dominance. A plant’s apexes are the tips of its growing shoots, which receive a lion’s share of auxins to get them growing in spring. Apical dominance is the result of this extra boost given to shoot tips.

As for commercial rooting hormone products, you may see some that contain “IBA” rather than gibberellins, cytokinins or auxins. IBA is short for indole-3-butyric acid, which is one of the auxins and a powerful stimulant for root growth. Weeping willow trees have an abundant supply of IBA in their young, first-year branch tips.

You easily can make your own root hormone dip by taking first-year cuttings of the final 6 to 8 inches of young willow tips, stripping the leaves and cutting the yellow-bark stems into 3-inch lengths. Fill a quart jar with them, cover them with water and set in a cool, shaded place for four weeks. Then dip your cuttings in this solution before planting.

Jeff Cox is a food and garden writer based in Kenwood. Reach him at jeffcox@sonic.net.