Warmer winter opens buds

Q. Will the warm temps have adverse effects on plants like magnolias and daylilies and spring bulbs?

Bruce from Youngstown

A. Yes. No. Maybe? It depends on the plant and what you’re seeing right now. Plants rely on environmental cues – day length, temperature, soil moisture, etc. – to know when to grow, flower or go dormant. Dormancy is a way to avoid unfavorable growing conditions, and in Ohio that would be cold temperatures accompanied by short days. The longer a plant is exposed to increasingly lower temperatures and shorter days, the more cold-hardy it will remain through the winter.

Many plants begin this process in late summer or through the fall before reaching maximum cold hardiness levels in December or January. In what we call a typical year there’s a steady decrease in temperature that provides continuous feedback to the plants that going dormant is the correct decision. That’s not always the case, as we have seen, and we will most likely see these temperature fluctuations during this unusual winter.

Blooming or swelled flower buds are the result of this warmer weather, which has inhibited plants from entering their full dormant state. Although the plants are still experiencing short day length, the higher temperatures are able to override any other signal and resume growth.

There’s also the phenomenon of chilling requirement that adds another level of complexity to plant dormancy. Chilling requirement is generally defined as a minimum length of time a plant must be exposed to a specific range of temperatures before growth can resume. The most commonly used temperature range is 32-45 degrees.

Chilling hours required for a plant species can vary greatly between individuals and different cultivars. For example, highbush blueberry chilling hours are typically between 300 and 800 hours. Plants originating from northern latitudes typically have shorter chilling requirements compared to those from more southern regions. A lower chilling requirement allows plants to resume growth in the spring more rapidly so the plant can take advantage of our relatively shorter growing season.

Sustained warmer-than-usual fall temperatures this year have resulted in rapid accumulation of chilling hours, meeting the requirement for many plant species – which have now begun to flower or have swollen flower buds. A flower that blooms in December is one less that will flower in the spring to produce fruit. That’s the “damage” we will see come spring. Also, flowers in bloom or swollen are more susceptible to low temperatures, which increases the chance for damage. So, we may see fewer flowers on some species. But weather experts have predicted a warmer winter (due to El Nino). Mulching is not recommended, but one caution: Dark-colored mulch (bark, etc.) will actually warm up faster and hasten emergence. The difference in soil temp between dark mulch and lighter-colored mulch can be as much as 30 degrees on sunny days. For perennials and bulbs that have emerged, just leave them alone. Once spring is here, you may need to cut back any damaged foliage.

Today’s answer is provided by Lee Beers, Extension educator for agriculture and natural resources in Trumbull County. Call the office hot line at 330-533-5538 to submit your questions. Regular clinic hours are over for the growing season, but you can still call and submit questions. Hours vary throughout the winter season.