Sunday, March 27, 2016

Is it Safe to Plant Summer Annuals?

You would think so, given that the garden centers in the big box stores are bursting with blooms. Two weeks ago, most of this bloom was from spring-blooming perennials and annuals like phlox and dianthus and snapdragons, but in the last week, tender summer annuals have appeared in great numbers. Is it time to plant summer annuals like salvia, zinnia, vinca, and impatiens?

According to the National Weather Service, the "average" last freeze date is March 28. This means that there is still a 50% chance of a freeze occurring.  Another way to think about this is that if you list all the historical last freeze dates for Memphis by year in date order, half of them occurred before March 28 and half of them occurred after. The latest recorded freeze date for Memphis is April 16.

Another thing to think about before buying your tender summer annuals is that, even absent a freeze, these plants don't thrive in cool weather. They like warm air and soil temperatures and will sometimes just sit there until they get temperatures more to their liking. If a cold snap occurs, they might not die, but they might not fully recover either. One year, I bought annual salvia after a temperature dip. It looked a little stunted but I did not see any obvious tissue damage, so I assumed it would recover. But it did not grow, and I eventually replaced it.

So what should a gardener to do? We have an old family friend who never plants anything tender until after May 1. This is probably a good strategy in terms of plant health, but the best selection of plants in the garden centers is usually earlier than that. So I plan to wait until mid-April and shop at my favorite local grower. (Local growers time the availability of their plants to be more in line with the best planting times for the geographic area. So petunias might be available a few weeks before vinca is available.)

Don't be fooled by this warm winter and seemingly early spring. Weather forecasting is getting better but Mother Nature still fools us. Besides, it seems to have been an especially good spring for pansies. Why would anyone be in a hurry to replace something looking like this?

(And speaking of pansies, don't forget to fertilize them. Barring a heat wave, they'll perform for at least another month but they need to be fed.)

One final word: this discussion has been about setting out ornamental plants. If you are planting seeds of these same plants, that's another subject entirely.

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