Gardening on the Cheap: Stretch Those Annuals

Sweet potato vine (Ipomaea batatas)Long on planting space but short on plants? Many of the “annuals” we purchase in spring are actually tender tropical perennials easily produced from cuttings. Why not root new plants from ones you’ve already bought? Or, arrange a cuttings swap with friends. Sure, the cuttings will take a little while to catch up. But as the former owner of a tropical plants nursery, I can tell you that in the increasing warmth of late spring, tropicals are gunning their engines, ready to grow.

Here’s a list of fast-growing selections whose cuttings will root within three or four weeks if kept in a warm, well-lit location: coleus (Solenostemon); sweet potato vines (shown), like chartreuse Ipomoea batatas ‘Margarita’; flat-leaf moss rose (Portulaca olearacea); angels trumpets (Brugmansia); chocolate sugarcane (Saccharum officinarum ‘Pele’s Smoke’); ornamental sages (Salvia); and plectranthus, like the luscious silver Plectranthus argentatus.

In fact, the list of possible plants is huge. How can you tell if a tropical plant will form adventitious roots along its stem? Try it! Or, to be a little more helpful, as long as the plant’s leaves form at nodes along the stems instead of sprouting from a central crown, it’s worth taking a chance. After all, what have you got to lose but a single shoot?

Taking cuttings is easy—just snip four- to six-inch shoots from the tips of your plants. You can use shorter cuttings, as long as they have at least two sets of leaves, but larger cuttings produce bigger plants faster.

Many tropicals will root when dropped in a glass of water, but I don’t recommend that system. The young, tender roots are too easily damaged when planting out. Instead, scrub small nursery pots in hot soapy water and fill them with a fast-draining but water-retentive potting mix. Water lightly to settle the soil. With a pencil, poke a hole for each cutting. Remove the lower leaves from your cuttings and slide them into the holes, being careful not to bend or damage the stems. Make sure you get a leaf node or two underneath the soil. Some tropicals root all up and down their stems, but others will only sprout roots from the nodes.

Gently press the soil around each stem to remove air pockets, then water again. Keep the plants in light shade for the first three weeks, then gradually introduce them to more sun. It’s natural for new cuttings to wilt a little bit, so be careful not to overwater them. Soggy soil is more likely to cause stem rot than to cure wilting.

It’s that simple—and before you can say Portulaca olearacea, you’ll have new plants!

Pictured:
Sweet potato vine (Ipomaea batatas) is one tropical plant, often grown as an annual, that will root quickly. Buy one and make yourself some more. Image by Forrest and Kim Starr.

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