When spring frenzy possesses gardeners, we tend to start planting things willy-nilly. The snow that fell over much of the Front Range on April 11 was a bitterly cold reality check.
Although many retailers have been offering warm-season annuals and vegetables for several weeks, it is just now time to start thinking about putting them out. The rule of thumb is two weeks after the average frost date for your area. For me, and most of us below 6,000 feet, that’s around the first of June.
Warm-season annuals and vegetables require warm soil and nighttime temperatures that stay above 50 degrees F. Though tomatoes, eggplant, pepper, squash plants and cucumbers might survive lower temperatures, they may never recover fully.
Seeds of basil, corn, pumpkin and all types of beans may simply rot in cold soil. By the time you realize they aren’t coming up, you’ve lost several weeks of growing time, a luxury we can’t afford with our short growing season.
The same is true for warm-season (also called tender) annual flowers such as ageratum, coleus, impatiens, Madagascar periwinkle, New Guinea impatiens, plectranthus, portulaca, flowering tobacco and sweet potato.
But the essential information is almost never on the plant’s label, so a smart gardener checks a good annuals guide. (I use an old copy of Taylor’s Guide to Annuals; recent introductions I look up online.) When in doubt, the safest thing is to treat any plant you don’t know as tender.
When I purchase annuals and vegetables, I separate them into hardy and not. Petunias, gazanias and verbena go outside onto my covered back patio, where I protect them with a frost blanket on cold nights. If a hard frost of below 20 degrees is predicted, they go inside overnight.
The non-hardies spend warm days on the patio but at night go inside onto a tarp in the family room, where the 60-degree thermostat setting is their ideal environment. They don’t go back out in the morning until it warms up to 50.
Admittedly, moving flats of plants inside and out is a lot of hassle, plus it means turning the house into a greenhouse at night and on cold days. (A couple of weeks ago a black widow who’d undoubtedly stowed away in the herbage, made its way to the guest bathroom, where it scared the bejeebers out of me. They don’t usually move in until late summer.)
The last week in May, my botanical sun lovers gradually spend more time in the sun. If the weather cooperates, I start leaving them outside with a cover at night.
Alternatively, you could wait until June 1 to buy your tender flowers and vegetables, but with this method, the plants at least double in size and are fully acclimated by the time it’s warm enough to plant them outside in pots or in the garden.
But in any case, always keep the frost blankets ready — June snow isn’t unknown in these parts.
Marcia Tatroe’s most recent book is “Cutting Edge Gardening in the Intermountain West” ($29.95, Johnson Books). E-mail her at mtatroe@q.com
