Growing Concerns 585: Store plants for next year, dogwood defoliators

Early Fall!

Dig and dry tender tubers for next year or read and try tricks to save them in-ground


Dear Janet,

How can I keep a tuberous begonia, caladium, some cannas, dahlias and a dwarf palm tree from my garden for next year?


Dear S.T.,

Dig them now, pot up the clumps or divisions and grow them as houseplants over winter.

Or, to hold a begonia, caladium or canna as a dormant root, cut it back or let it be cut back by the frost, which will kill the top but not the root. Dig it and shake off excess soil. Don't break any big roots or nick the tuber, as fungi can enter through wounds while it's in storage.

Invert the clump on a screen in an airy, warm place for a few days to let the soil air dry and the tuber cure. When most of the soil can be crumbled away from the root mass, wrap newspaper around the soil-clad tuber and put it in a paper bag full of crumpled newspaper. Alternatively, bury the clods in a box of clean, sharp sand or peat.

Now, the tough part. Find a storage place that is cool and not too dry. 50 degrees is perfect for the begonia and caladium, 45 for the canna and dahlia, and about 50 percent humidity for all. A Michigan basement or root cellar is ideal, but those few gardeners who have such a space could fill it ten times over with roots that their friends have no place to store.

As for the palm, it depends on the species. Check with the garden center that sold it. Most species have to be kept growing all year, frost-free.  Consult a book to see if your bamboo, banana, palm or another tender plant might be allowed to winter outside under deep mulch, with special care.

Short reports

Overgrown shrubs and vines overwhelming you?

Hold the shears, if you plan a significant cut-back. It is not good to prune a woody plant while its leaves are falling. During that time its twigs and branches harden off for winter using compounds withdrawn from the leaves. Wait, and prune several weeks after leaf-fall ends, or in late March or early April next year.

Outwitting dogwood defoliators.

Liz wonders about caterpillar-like critters that are stripping her yellowtwig dogwood. White and fuzzy at one point in their development, the culprits are now greenish, smooth, and striped.

Those are dogwood sawfly, Macremphytus tarsatus. They pupate like caterpillars, but emerge not as butterflies but small flies. These mate and lay eggs on the undersides of dogwood leaves in June. They're common on native graystem- and redtwig dogwoods in the fields and marshes.

Although they do little lasting damage and are only numerous every few years, a new shrub like yours would be better off keeping all the starches produced by its leaves toward quicker establishment.

This sawfly overwinters in rotting wood. The larvae may already be wandering off in search of a fallen branch or decaying wood siding to call home. Many will be eaten by predators before next June but some may find their way back. Reduce that chance by placing rotting log(s) under the shrub. After the killing frosts come, collect and burn that wood.

Put a magnifier on your wish list for the holiday season.

Every gardener can use a hand lens or a six- to ten-power loupe as sold at camera stores. If L.G. had looked through a magnifier at the catalpa leaf she sent to me, there would have been no question of what leaf spot it might be. The nature of the problem would have leapt out so that L.G. wouldn't have thought "disease" and "fungicide" but leaf removal and then a close watch and perhaps an insecticide next year.

The leaf was mined, not infected by a fungus. Mines are excavated within a leaf. In the twisting, turning tunnels sawfly larvae and pupal cases are still visible through the paper-thin leaf surface. I think if you had seen them, L.G., you could have guessed that they might overwinter in the leaf litter. Clean up and destroy or hot compost all the leaves.

Leaf miner is nearly unheard-of in catalpa, but was reported in scientific papers at least once before in your area, in 1982. So you may never see it again. But do watch next June for mining, and in that case check into appropriate insecticides.


Green thumbs up

to a healthy plant's ability to look after itself. Catalpa is one wonderful example. When a leaf is chewed by catalpa sphinx caterpillar, that leaf secretes a nectar that attracts ants. Then, the ants defend the leaf against the caterpillar!


Green thumbs down

to those who'll write to me in the future about their lawn problems and tree trouble, without thinking to mention that during the 2004 Ryder Cup they parked twenty cars on that lawn. That compacted the soil, killing roots and impeding new root growth. Next year you'll see poor leaf growth and increased pest problems. What you charged for parking should have included greens fees for core aerating the lawn and vertical mulching the tree root zones.


Originally published 9/25/04