Q . I have two indoor plants, a schefflera and a ficus, which are about 17 feet tall. They both started out 20 years ago as typical supermarket plants. I have transplanted them a couple of times into large pots, the last time about 10 years ago. They are now so large and heavy that there is no way I can move them into larger pots. The schefflera seems to be doing OK, but the ficus is kind of sparse. My guess is that it is totally rootbound. Is there some course of care I could follow short of transplantation that would maintain their health and extend their lives?

A. You can keep mature houseplants at a constant size, but you must prune both the branches and the roots, and the project is best done when the plants are repotted. You can use the same pot, or even a smaller one.

Schefflera and weeping fig take well to pruning, so you can remove as much as half the branches to keep the plant in scale with the pot and contain its growth. Cut the longest branches back to the main trunk.

Prune the roots by teasing away the soil from the outer portion of the root ball and clipping off any exposed roots.

Repot the plants, and keep the soil barely moist. When you see new growth, give them a monthly dose of fertilizer and water them more thoroughly, allowing them to dry slightly between waterings.

Q. My purple wisteria has been vigorous, healthy and in flower each spring for a decade. Recently I have noticed that all the leaves have slightly yellow blotches and the vine is dropping leaves. My local nursery advises that it probably has a terminal virus and that there is nothing I can do. When I check the Internet, I get a wide variety of answers, some suggesting that I add various nutrients to the soil. What's your advice?

A. The malady could be a virus. Wisterias are often propagated by cuttings, and cuttings from virused plants will be infected from the start. The disease can remain hidden for many years and then appear under certain environmental conditions.

Alternatively, the spots might have been caused by a fungal or bacterial infection, possibly Phyllosticta wisteriae or Pseudomonas syringae.

I would do nothing more than rake up the fallen leaves. Prune it near the end of the summer to promote good flower bud formation and to keep the vines under control.

Scott Aker is a horticulturist at the U.S. National Arboretum.