I love spring. Everything is waking up, the sun is out, and my energy level peaks. I am itching to get my hands dirty and get back into the gardening groove.
Spring is a glorious time here in North Carolina. But don’t be fooled by the early warm temperatures. Invariably we will receive one last frost in late March to late April before winter temperatures finally call it quits.
Frost is a condition that occurs when temperatures at night drop to between 29–30 degrees F. The average last frost date for our area is April 13, however if you plant your annuals based on that date you may learn the hard way that you should add the standard deviation, which is 12 days for Durham, to the average frost date which equals April 25. This will decrease the probability of experiencing a frost to about twice in a 10-year period. If you want to lower your chances even more then wait another 12 days until May 7. This will change the odds of a late frost to about twice every 100 years.
So what do you do with all of the plants in your garden that have put out new leaves and flowers that may be lost in a frost event? Cover them up! If you have a row cover that has been specifically manufactured to protect plants from frost, that’s great, if not sheets and blankets will do. Small herbaceous perennials and shrubs can easily be protected this way, trees however can not. If you have flowering fruit trees, expect to experience some losses. You may be able to protect some of the buds by covering individual flowers temporarily using small paper bags secured with string. While this is a lot of work, on a small scale it can be done. Remember protective covers will need to be removed after the frost event is over to ensure pollination.
Potted plants should be grouped together and temporarily moved to a protected location close to a house or structure. Buildings do radiate heat and can provide just enough added protection to ensure plant survival. Potted plants are particularly vulnerable to temperature drops since their roots do not benefit from the extra insulation the soil provides.
To find out more information about Average Last Spring Frost for Selected North Carolina Locations go to http://www.ces.ncsu.edu/depts/hort/hil/hil-707.html or contact the Durham County Extension Master Gardener volunteers at firstname.lastname@example.org or 919-560-0528.
Michelle Wallace is the Consumer Horticulture Agent for the North Carolina Cooperative Extension Service in Durham County. You may contact her at 919-560-0525.