If Your Wisteria Is Listless, Try Pruning to Restore the Bloom

Question: We planted a wisteria in a big pot three years ago when it was in full bloom, but last year it had only a few flowers and this year none at all. It’s full of leaves, though, and we’ve been fertilizing it often, so what do we need to do to get flowers?

--G.G., Torrance

Answer: It often takes time for wisteria to settle in and start flowering, and fertilizing will not help since it only encourages more leafy growth, not blooms.

To get flowers, you must prune, and in California the best time is in summer, from June through September. You must “control the monster,” according to Lucy Tolmach, director of horticulture at Filoli in Northern California, a public garden in Woodside famous for its spectacular two-story wisteria.

There are two kinds of growth on wisteria, the vigorous vegetative twining kind and the shorter fingerlike flowering spurs that form near the base of twining stems.

These flowering spurs, similar to those found on apples, produce the fat buds that become spring’s graceful flowers.

To encourage flowering spurs at the base of each twining shoot and manage the size of the plant, Tolmach says whack back every twining stem that emerges from the canopy of leaves. Cut each back so it is roughly even with the rest of the plant. They will immediately start regrowing, so cut them back again. Each time you cut back a twining stem, you make more flowering spurs, so Tolmach suggests pruning monthly in summer.

When you cut back a twining stem, try to leave three or four buds, but don’t worry if there are more. The gardeners who work on Filoli’s towering wisteria with pole pruners often just have to approximate. It’s almost as simple as pruning a hedge, despite some rather complicated instructions found in garden books.

In winter, when plants are leafless, you can tidy them up, removing dead and crossing branches, plus stems that are growing in the wrong place. At Filoli, they work to preserve the lean, evenly spaced lines of the vines with winter pruning, which is why they are so graceful and elegant. The vines flower as profusely as they do because of the constant summer pruning.

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Q: We are preparing an old lawn area so we can put down new St. Augustine sod. We thought a first step would be to “weed and feed,” then bring in some topsoil and lay the sod. Will that work?

--L.S., North Hollywood

A: Lawn products that have herbicides and fertilizers mixed together in one package--the so-called weed-and-feed formulations--are not for new lawns or yet-to-be-planted lawns. They are for existing lawns, and the herbicides in them either kill broadleaf weeds in grass lawns or contain pre-emergents that prevent all seeds--including lawn--from germinating.

Most weed-and-feed formulations contain selective herbicides that can distinguish between plants with bladelike leaves--the grasses--and those with broad leaves, such as dandelions. They can takes oxalis out of a grass lawn but cannot get rid of devil or Bermuda grass in fescue lawns because both are grasses. They will not kill weedy grasses that you might want to eradicate.

To prepare an area for sod or seeding, most lawn companies use Roundup (glyphosate), a systemic herbicide that kills everything it touches, so you want to be very careful that the spray does not drift onto desirable plants. Roundup is translocated to the roots, so it also kills roots and spreading rhizomes. This makes it a very effective herbicide, especially on Bermuda and St. Augustine grass, and you can plant your lawn just days after using it

There’s no need for topsoil. Simply rototill or loosen the existing soil and plant.

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