GREEN PATCH

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For the Beginner

Question: I’d like to expand my herb garden, adding more perennials and shrubs. Can I do it this fall, or should I wait until spring?

Answer: Unless you ­already have the plants you want, you may be better off waiting. Nurseries and garden centers often promote fall planting, but they may be sold out of many varieties for the year. Check the inventory carefully, and avoid leftovers that have been growing in the same pots all summer, their roots crowded and their tops leggy or cut back. Plants like this may survive, but they’re second-rate and not worth full price. Even an attractive sale price is no bargain if the plant dies over the winter.

If you do find good-quality plants, if you already have plants that you want to set out, or if you want to rearrange or transplant herbs that are presently growing in your garden, the success of fall planting depends on your climate, the weather during the winter following planting, and just plain luck.

In Zones 8 and warmer, where the ground doesn’t freeze, you can plant anytime from fall to spring with generally good results, but a sudden and severe cold snap or unusually heavy winter rains that saturate the soil can kill even established plants.

In Zones 7 and colder, fall planting has no real advantage and can be risky. You may have heard that fall planting is advantageous because plant roots continue to grow after the tops go dormant, giving anything planted in the fall a head start. That’s true to some extent where winters are mild, but in cold regions, fall and winter root growth is insignificant compared to what happens in the spring. And several things can go wrong:

• The herb may freeze to death. A plant is hardier if it’s had all summer to get established.
• The roots may rot. This is especially likely in regions that have a spring “mud season”, when the subsoil remains frozen and the surface soil is soggy. New plants are more vulnerable to rotting than established plants.
• Repeated freezing and thawing may heave the plant’s roots out of the ground. Large plants can be lifted a few inches, and small plants can pop out altogether. Exposed roots are susceptible to freezing and/or desiccation.