I planted a small wisteria vine that has flowered and performed well. How should I be pruning it to keep it under control? P.L., Sudbury, MA
Both grapevines and wisteria are considered high-maintenance plants. Left to grow on their own, they will quickly dominate their area and become unruly, eventually requiring drastic corrective measures. It is wise to prune and train their stems and branches at least once — and preferably several times — each year. Once you understand the basic principles, you should be able to easily do this yourself without hiring a professional.
Always train the branches to grow on their supports, not twine around them. It’s important to never allow stems to get a grip around a post or trellis, because as they increase in size, they will eventually damage the supports and may even pull them down.
Grapevines and wisteria can be pruned any time of year, but it’s easier to see their branching patterns when they have lost their leaves and are dormant in late fall or before growth begins in spring. Fall pruning can cause stem dieback in severe winters, and the stems tend to “bleed” when they’re pruned in late winter or early spring, but neither of these results is detrimental for most cultivars that grow in this region.
Look for books, articles, and information on the Internet for more details; a bit of easy periodic maintenance will afford you years of pleasure.
The instructions for planting Sempervivum suggest using “grit” as mulch so the plants don’t freeze in the winter or rot in the summer. What is grit and where can you get it? B.P., Shrewsbury, MA
The botanical name Sempervivum (houseleek or hens and chicks) is derived from the Latin words semper (“forever”) and vivo (“to live”). But to live up to its name, the plant’s roots cannot sit in water for very long or they will rot. In their native habitat, alpine succulents such as houseleeks and stonecrop (Sedum) grow on mountaintops where the soil is perfectly drained; typical home garden soil tends to be less well drained. Most commercially available hardy succulents have no problem tolerating cold winters, but in order to survive, their roots must stay anchored in the ground without rotting. Mulching with grit will help even out soil temperature fluctuations to reduce the risk of “heaving” (when the roots become dislodged as the ground alternately freezes and thaws in winter).
Grit is simply coarse sand or fine gravel that contains minimal amounts of clay. It’s commercially available at many garden centers, and bagged soils for alpines already contain the right proportions for good drainage. You can produce small amounts of grit yourself by running water through builder’s sand in a coarse sieve or screen.