Dear Miss Floribunda,
The forsythia in my backyard is blooming, so I’ve gone out and pruned my roses, as advised by you and some others. What I’m not sure about is when to put out the seedlings I started indoors this year for the first time. Although I’ve looked up what our last frost date should be, different sites give different answers. Also, even if I were sure, I know that some plants tolerate frost better than others. I usually plant peas directly in the ground in March, and I even think they prefer a cool air temperature. Probably even a very light frost would kill my tomato seedlings if I planted them now. Is there something like the forsythia-in-bloom rule that might help guide me here?
Curious on Crittenden Street
Planting your seedlings outside is not just about frost and how severe it is, nor air temperature, but it’s also about the warmth of the soil. When the soil warms to 60 F or higher, it’s safe to bring out seedlings for tomatoes, eggplants, peppers and other warm weather vegetables. You can plant seeds for summer squash and zucchini directly in the soil at that time, too. Usually late April is safe in our area, but you might want to invest in a soil thermometer to be sure. It’s not a bad idea to bring your seedlings outdoors earlier, keeping them in their pots and bringing them back in the house at night. This will help them gradually adjust, or “harden off.”
However, what you’re asking for is quite valid, and it has a name: phenology. Literally, it means “the science of appearances,” and is the study of such seasonal biological phenomena as bird migration, animal hibernation, leaf-color change in fall, and the sprouting and flowering of plants. When you live in a capricious climate, as we do, it helps to watch what is happening outside your window.
While this is an old science, it has become trendy of late under the name “springcasting.” Forsythia isn’t the only plant watched, but the blossoms of cherry and apple trees, dogwood and lilacs are among other flowering plants used as markers.
The Japanese, by the way, began recording the flowering of their cherry trees as early as the ninth century. In the western world, Carl Linnaeus (known as Carl von Linné in his native Sweden) recorded his observations systematically in the 18th century, along with other amazing achievements that earned him the title “Father of Ecology.” And, if you’ve ever looked at an Old Farmer’s Almanac, you have seen quite a bit of phenological lore — including what phase of the moon is best for planting root vegetables, why grasshopper eggs hatch when the lilac blooms, what the signs of imminent rain are, and so on.
Folk advice is of varying value: It won’t help to know that it’s time to plant garlic when the feet of the snowshoe hare turn white in the fall if there are no snowshoe hare in your area. Nor do I really want to peer up into oak trees to see if the leaves are the size of squirrels’ ears before I plant corn.
However, I know that it really is true that a good time to plant corn is when apple trees finish flowering because I actually have apple trees. From my own observation, I have learned to wait to plant cool weather veggies until crocuses pop up in my yard — and that includes potatoes and peas. When my next-door neighbor Patapanelope’s lilies-of-the-valley bloom, I know it’s safe to set out tomato plants.
The point is to find floral phenomena around you that reliably indicate the level of light and degree of soil temperature appropriate for certain garden activities. You already know that when your forsythia blooms, you can start your spring pruning. My neighbor several doors down, Mr. Greenspan, takes this as a sign to fertilize his lawn.
Is there a floral signal that will tell you when to set out your tomato seedlings? A marker you can use is the blooming of bearded iris in your own or nearby gardens. In our microclimate, that means the soil is warm enough for you to set out tomatoes and all your summer seedlings, as well as to plant seeds of tender annuals and vegetables. I’ve been told that if you have a lilac near you to watch, you can plant beans and squash when it’s in bloom and cucumbers and squash after the flowers fade. However, I still advise buying a soil thermometer!
To learn more fascinating lore from seasoned gardeners and participate in a plant exchange, please come to the next meeting of the Hyattsville Horticultural Society on Saturday, April 15, at 10 a.m. It will take place in the lovely back garden of Mary Jane Stevens and Robert Meyer, 3925 Nicholson Street.