Although everyone had plenty of warning, did the sudden drop of temperatures around the freezing point in the wee hours of Sunday, March 13 seem completely unexpected considering all the warm weather we’ve had? Brunswick saw the temperature dip to 29°F, St . Simons, 32°F degrees, Jekyll, 34°F, albeit all lows were for a short amount of time. Typically, the Zone 9a frost-free date is March 15, so Mother Nature just snuck one last cold snap within that time frame. She’s done it before and will do it again. She certainly had me scurrying to cover cold sensitive outdoor container plantings of jade plant and Christmas cactus that reside on our front porch as well as two small citrus trees planted last spring. I even had to fetch 10 trays of sprouting tomatoes, cucumbers and squash I’d planted two weeks ago in a brand new 8×16 foot greenhouse because it didn’t have any heat source. I placed them in the garage for the night. Luckily, flowering blueberry and pear, emerging leaves on hydrangea, blooming perennial salvias and unfurling fronds of ferns seem to have escaped injury.
I also had to cover the first plantings of petunia, one of a variety of shoulder crops my husband and I have planted over the many years of coastal living. What is a shoulder crop, you ask? A shoulder crop is a crop used to help a flowering bed “hold over” from late winter to late spring and again from late summer to late fall. It is a crop usually planted in mid-March through mid-May or mid-September through mid-November, windows of time when the weather is neither too hot nor too cold. Plants used in shoulder plantings allow gardeners in Zone 9a to use annuals and biennials that tend to do well with night temperatures of 60-70 °F and day temperatures of 70-80°F. Rainfall and sunlight are generally sufficient to allow these plants to thrive in these two eight-week windows. The drawback is cost. Budget-wise folks will tell you to plant for summer and winter, waiting patiently for temperatures to either warm up or cool down. Because I like a means of extending these two growing seasons but have a limited budget, I plant shoulder plants in containers rather than in beds. However, I have seen breathtaking large displays of shoulder plants with those who don’t have to budget, outside of arboretums. In these rare circumstances seen in home landscapes , I have had to chide myself about plant envy. Think a 50-foot wide and 10-foot deep bed of yellow daffodils under a live oak, intended to thrill for just four weeks of early spring and then see the display rotate four to six times a year, temperature dependent.
Since we are currently in the spring shoulder season, I thought I’d share a few of the favorites I have on my list: dianthus, petunia, geranium, diascia, calendula, African daisy (Oteospernum sp.), edging lobelia, sweet alyssum , Million Bells (Calibrachia sp.), dahlias and snapdragon. You can find these at local home improvement stores and local nurseries but don’t expect them to make it through the heat of our summers unless you have a unique microclimate! You may have planted some of these in the late fall of 2021, but now is when they will recover from colder temperatures and look great … until the temperatures get too warm.
This brings me to a slightly different topic. Did you know that there is an AHS (American Horticultural Society) Heat Zone map available in addition to the USDA Plant Hardiness Zone Map? This map, developed in the late 1990s, parallels the plant hardiness zone map and is based on the number of “heat days” a plant can tolerate over 85°F. Combined knowledge of the two is a most useful tool for those of us living in a climate that allows for 12 months of flowering plants. Observe what is growing around you and ask questions to learn which plants grow best without a more prolonged cold season and which plants tolerate warmer nights in the summer. Spring flowering plants like tulip, hyacinth, lilac, forsythia and peony have chilling requirements to bloom, and summer annuals, like petunia and geranium need cooler night temperatures in summer. Therefore, they don’t perform well in most locations in the coastal south. Of course, there are always exceptions to the usual answer: “That won’t grow here.” Gardening is always an experiment and sometimes, it takes both experimentation and experience to provide the right answers for your landscape.