Question:
What are the general rules for mulching plants for cold weather protection? I see very little being done, but I’m new to the area.Answer:
- Mulching plants with straw and other materials are used to insulate their roots when the ground freezes.
- Fortunately, the ground never freezes in the Bay Area, so mulching isn’t necessary. However, we do experience freezing temperatures that can damage or even kill many plants. Summer color and other soft tissues, such as herbaceous plants, are the first to suffer.
- The key factors in damage to woody ornamental plants are how long temperatures remain below 32 degrees after sunrise and how much moisture remains in the ground.
- Cold acts as a desiccant, rapidly pulling moisture from plant cells. This results in burnt or brown foliage, and in severe cases, the plants may not recover. Therefore, it’s essential to water container plants before a frost.
- Frost damage occurs when the air is still and is never a concern during windy conditions. Since plants have no central nervous system, wind chill does not affect them; only the actual temperature does.
- Herbaceous plants like parsley, basil, and others generally don’t survive prolonged cold and must be replanted each spring. Woody varieties such as sage, oregano, rosemary, and others are unaffected by our winter temperatures. We protect cold-sensitive plants such as Citrus, Bougainvilleas, Mandevillas, and Hibiscus with Bonide Wilt Stop. Wilt Stop creates a protective, transparent film or barrier on the leaves. I like to think of it as ‘ChapStick’ for plants.
- Additionally, plants can be covered with N-Sulate or a similar plant blanket. N-Sulate is a UV-treated, reusable tarp-like cover available at many garden centers. It can be draped over groups or clusters of plants.
- You could also use sheets or blankets, but plastic sheeting is not recommended. Plastic conducts cold directly through the material, whereas these other coverings do not. If plastic is used, it should be ‘tented’ over the plants to avoid contact with the leaves. It’s not advisable to wrap plants long-term as we do with water pipes during winter.
- Typically, the coldest temperatures are expected in January and February. Do not prune any cold-related damage until March.
Question:
The onions I planted this year had a problem: seed stalks developed when the plants were still tiny. Why do onions go to seed so early?Answer:
- When Onions go to seed, it's called bolting. The main cause of bolting is weather-related stress from sudden temperature changes.
- Onions are best planted in the fall and late winter through early spring. Onions planted from April through June tend to bolt as soon as temperatures rise into the 80s. Onion sets are now available, along with the Sweet Bermuda Onions, Stockton Red, Torpedo, Yellow, and White, which are sold at many garden centers.