Potted heavenly bamboo should be treated as large bonsai

Q: At my parents home, Dad has always had heavenly bamboo planted in two big pots that sit at the front entrance. Not getting around as well as he used to, the bamboo is looking “not as full” as they have in years past. What would you suggest I do for the heavenly bamboo to bring them back to past full looking happiness? — H.B.O., Albuquerque

A: Since the heavenly bamboo — Nandina domestica — is living in containers, you’ll want to think of them as large bonsai plants. So here’s what I’ll suggest.

When the weather gets a bit cooler, perhaps in mid-to-late August, I’d go ahead and cut out to ground level a couple of the taller older branches or canes away. That will convince the plants to concentrate on refilling the balance of the plant.

Then, it could be quite a bit of work, but I’ll suggest you uproot them completely, knocking away and removing as much of the old potting soil as possible. Get all the “exhausted” soil out of the pots. If the dislodging of all the soil rearranges the pebbles or rocks at the bottom of the pots make sure to reseat them so once refilled, the soil stays in the pots.

Take a good look at the root structure and put yourself in a bonsai frame of mind. You’ll want to trim the root mass. It probably looks like a circular globe of roots. Your job will be to wiggle the roots free so they aren’t tied up. Trim away any really old root, making sure to cut away any damaged root too. Don’t go nuts with the clipping away, but you do want to lessen the root mass by maybe half. Be sure to use really sharp and clean tools for this part of the project. Don’t tear or break the roots. Cut them cleanly away.

Since the plants are unpotted, now will be the time to cut away the older canes too. Take them down as close as you can to the beginning of the plant. Come time to set the bamboo back in the pots, you’ll want to use fresh potting soil. I will recommend mixing in some clean sand with the potting soil too. No, not sandy soil from your yard. That might contain a whole host of seeds and bugs that you do not want to incorporate into the heavenly bamboo’s home. Packaged sand can be found at all home improvement stores and most nurseries. Mixing in the sand to the potting soil at a rate of ¼ sand to ¾ potting soil should make a nice mix for the bamboo.

Now remember that since you’ve trimmed the root mass, you’ll want to put more soil into the pot before, so when you set the bamboo back into the pot it doesn’t sit too low. Your aim is to cover the root mass only, leaving the green parts above ground. But don’t plant too shallowly, either. It’s a fine dance, but you can see what needs to happen. Tamp the soil into the pot firmly so the roots become stabilized, adding more soil if necessary, and voilà, you’ve successfully rejuvenated the heavenly bamboo.

Give the pots thorough slow waterings for the next couple of days to be sure all the soil has dampened and the plants have seated properly in their freshened homes. You might consider offering a dose of properly diluted root stimulator but since the soil is fresh and you’ll be monitoring the watering, that isn’t paramount for their health. Remember to keep the plants watered through the winter months, too. Never allow the pots to dry out completely ever.

With some tender loving care, the removal of the older canes, trimmed roots and fresh soil, I’ll bet the heavenly bamboo rebounds for you and will make Dad happy.

Happy Diggin’ In!

Tracey Fitzgibbon is a certified nurseryman. Send garden-related questions to Digging In, Albuquerque Journal, 7777 Jefferson St. NE, Albuquerque, N.M. 87109, or to features@abqjournal.com.