When that first spell of warm weather with above-freezing temperatures at night comes along in spring, it's sometimes difficult to resist the temptation to get everything into the ground: plants, seeds, bulbs, rhizomes, and corms. Every year I wrestle with that impulse, especially when spring comes early to our zone 5a Cottage-in-the-Meadow Gardens, as it has for the past several years.

Many gardeners have their favorite methods for determining when those magic dates for planting finally arrive: In the region where I garden it's Good Friday for potatoes, after the Drei Kalte Männer* in May for plants especially susceptible to frost damage, specific dates on the calendar, and the various phases of the moon. For the more scientifically-minded, a soil thermometer does the trick.

I, on the other hand, prefer to let plants themselves tell me when it's safe to plant. Here is a list of plants I consult when I begin gardening each year:

· When forsythia blooms, it's time to plant the seeds of alyssum, carrots, cornflower, peas, poppies, and radishes.

· When cherry trees and flowering quince bloom, it's time to plant broccoli, cabbage, cauliflower, larkspur, onion, pansy, and snapdragon.

· When lilacs are in full bloom (as they are in our garden right now), it's time to plant the seeds of beans, corn, cucumber, marigolds, morning glory, nasturtium, petunias, squash, sunflower, and zinnias.

· When bridal veil (Spirea vanhouttei) and wild cherry trees bloom, it's generally safe to assume that the last frost of spring has passed. This is the time to plant all those frost-tender plants you've been eying at garden centers for the past month or so.


As I've indicated above, cool-season vegetables--including most salad greens, peas, onions and popular cole crops such as cabbage, cauliflower and broccoli--can tolerate temperatures slightly below freezing. Warm-season vegetables such as tomatoes, peppers, eggplant, squash and melons can suffer greatly, if air temperatures drop below 50 degrees, unless you've protected the transplants with cloches or some other plant-protection device.

ImageA special word of caution about caladiums and peppers: Caladiums are sensitive to temperatures below 50 degrees. Prolonged exposure will cause the leaves to droop and eventually the plant will go dormant right in the midst of spring. Those beautiful multi-colored leaves look great in stores and greenhouses right now, but if you want to keep them looking that way, don't purchase caladiums until the nighttime temperatures are consistently above 50 degrees. Alternatively, you can purchase them now and keep them in a warm, bright spot (no direct sun) until it's safe to plant them outdoors. Peppers also follow the 50-degrees rule. Their leaves won't be harmed much by lower temperatures, but they generally will not bloom well, if at all, if it's below 50 when its time for the plant to start producing flower buds. Hence, there will be few or no peppers.

ImageOn the other hand, there are plants that are amazingly hardy and survive even hard frosts in spring. A number of years ago temperatures plunged into the teens just as tulips and daffodils were about to bloom (some of the earlier varieties already had blossoms) and the garden perennials had poked their heads up about six inches out of the ground. I went to check on them the next morning and found that the tulip leaves had literally turned blue, the daffodil leaves were drooping to the ground, and the perennials were stiff as a board. I tried to bend a phlox shoot and it simply snapped in two. It was hard as a rock! I was convinced that every plant that had dared to venture above ground was doomed. Yet, much to my surprise, two days later there was barely any evidence of frost damage anywhere!

What are your favorite methods of determining when it's safe to plant? You can let me know in the space provided below.


© Larry Rettig 2008

Thanks to my wife, Wilma, for her gracious permission to use her photo. The lilac in the background has been growing in our gardens for over 50 years.

*Amana German for "three cold men," which refers to three succeeding nights of frost in May. After these have passed, it's considered safe to plant anything susceptible to frost.