Keep your favorite tender perennials growing

Keep your favorite tender perennials growing

Ken Druse’s book is a good guide on expanding any plant collection.

Ken Druse’s book is a good guide on expanding any plant collection.
As the nights cool down and I start pulling sweaters out of the closet, I can’t help thinking about the end of the season. I still count on another good month or two of garden-y loveliness but nearing the end of one season gets me dreaming about the beginning of the next season, and so the cycle circles.

And, dreaming about what I want in next year’s garden wakes me out of my end-of-season reverie to make it so. It’s high time to take cuttings of favorite perennials that are too tender to overwinter outside and too big to bring in.

I have spent most of the summer sitting at my writing desk (fingers crossed, the book will come out next fall) watching hummingbirds work a potted Stachytarpheta mutabilis ‘Variegata’ on the deck just outside my window.

The leaves of this porterweed are splashed with creamy variegation but the hummingbirds come for flowers that have spooled up long snaky stems in tight coral-pink clusters since July.

I’d hate to see that rather expensive beauty land on the compost heap. I could cut it way back and squeeze its container into my chilly entry porch (the “plantry”) for the winter but if I took tip cuttings I could overwinter 10 plants in place of just one. The more the merrier.

I would bet that most of us learned to weed before we learned to propagate. I did anyway. But just as weeding is a matter of training your eyes to spot particular species of seedling, propagating (tender) perennials by tip cuttings is a matter of identifying the right sort of growth that would grow into a decent clone.

Look for new growth that is neither too woody and stiff and already blooming, nor too soft and baby-fresh. Think Goldilocks. Stems that are flexible, sturdy and green are just right. New growth that hasn’t yet formed a flower bud is best, but those may be hard to come by while everything is going through the last huzzah.

In the morning before plants have transpired the day’s moisture away, remove a few fat tips below two or three sets of leaves and place them in water or a baggie until you’re ready to root them. Nip out the flower bud, which will divert the gotta-flower energy into gotta-root energy instead.

Keeping the leaves at the very tip, slice off a set of leaves one or two nodes below the tip right at the stem (use an X-Acto knife or scalpel for precision) and re-cut the end a half inch or so below that. The exposed cells, at the armpits where the leaves used to be, are versatile and full of hormones that will trigger the production of roots as soon as they’re “stuck.”

For an extra hormonal kick in the pants, dust the stem end lightly with rooting hormone powder available at most garden centers. Don’t lick your fingers after.

Snip the remaining leaves in half to prevent them from wilting and plant the cuttings in a container of moistened rooting medium such as perlite, vermiculite or sand, any of which will keep them standing upright, allow oxygen to pass through, hold moisture without being waterlogged and help ensure that while roots grow, gunge doesn’t.

Tuck the leaf nodes in below the surface and make sure the stem end is in contact with the medium, too. Keep the medium moist — if you don’t have a high-tech mist system, cover the container with a low-tech clear plastic bag and spritz the cuttings every day or two. And keep them warm but out of direct sun.

In a few weeks they should be rooted and ready for potting soil. Easy. But don’t just take it from me. The prettiest instruction manual ever, “Making More Plants,” by Ken Druse, is back in print.

Any plant that offers as much pleasure in one short season as my Hummingbird Central stachytarpheta did is worth every penny and I’d spend it all over again. But like weeding, propagation is an important skill to practice. The ability to keep favorite tender perennials growing for years of entertainment — that’s priceless.

Kristin Green is the interpretive horticulturist at Blithewold Mansion, Gardens & Arboretum in Bristol, where she’s worked since 2003. Follow her garden blog at