Monday, December 17, 2012

Spring Blooming Bulbs Leafing in December by Mary Small

Tulips Leafing in December Photo by Mary Small
Last time I checked the calendar it was December.  So why are some of my spring blooming bulbs leafing?  And what will happen to them following this recent cold snap?

Fortunately my plants (and maybe yours) don’t “think” it is spring! It seems that when fall weather is mild, some bulb plants send up a bit of green foliage. (Some bulb species produce green foliage whether or not the fall has been mild!) In most cases, leaves stay just a few inches above the soil  throughout the rest of the cold period. If the weather is really cold, foliage may freeze and turn yellow or brown and shrivel.  But generally new leaves appear in the spring followed by flowering.

Plants native to cooler climates have a mechanism to keep them from blooming or growing at the “wrong” time, called “chilling requirement”.  This is the number of hours a plant has to be exposed to temperatures between 32 and 45 degrees F before the plant can break dormancy.  Spring flowering bulbs, perennials and trees all have a chilling requirement, although it varies among plant species. Once a plant has met its chilling requirement, it “waits” until conditions are favorable for growth before leafing and flowering.  In our area, the chilling requirements can be met by around February.

Soil temperatures are one of the triggers that tell flowering bulbs that conditions are favorable and its “good to grow”. So we can help slow the progress of spring flowering by adding a mulch layer over the soil where bulbs are planted.  This helps keep soil temperatures cooler and slow the spring leaf and flower development.  If you haven’t applied mulch, go ahead and do it now.
Otherwise Mother Nature has things well in hand.  Enjoy your holidays!