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Control yourself from planting flowers too early

Ask the Expert Gardening
Coreopsis-in-Bloom
Like a number of other perennial flowers, coreopsis can be overly exuberant in some gardens. Adobe Stock

What to do this week: Spring is here, but March demands restraint. You are still only preparing for a battle that does not actually start until next month.

So don’t buy too many seed packets, or stress seedlings by starting them now indoors. Wait for April so they don’t outgrow their pots before May transplanting to the outdoor garden. Also, mud season is a good time to try to stay off the lawn and out of the garden until the ground is dry enough that you no longer leave compressed footprints, so don’t dig in fragile topsoil yet and tread lightly as you begin your spring cleanup.

What can you actually do outdoors? Plenty. Repair outdoor screens and furniture. Check yard waste pickup dates and instructions with your Department of Public Works. Turn your compost pile if you have one, making room for the organic debris soon to come. Prepare for container planting and re-potting plants by dumping the old soil into the compost to recharge it for future use, and then soaking the pots in a 10 percent bleach solution for several hours, followed by a rinse.

To welcome spring, cut forsythia stems on a warm day and put them in a vase of water to open indoors. Soon your garden will be full of life, so hang for returning migrants. Don’t buy those with perches, which just give predators a platform for stealing eggs.

Q. One plants dahlias just before Memorial Day, yet mine don’t bloom until just before frost sets in. I’ve started to plant them inside in late March to get them started. Yet still, I only get a few blooms before the frost kills them. Any advice?

A.W., Newton

A. Perhaps you are transplanting them outside too early. Try waiting until after Memorial Day, when the soil has warmed enough not to shock heat-loving dahlias (and tomatoes) and set back their growth. Dahlia tubers, which look a bit like sweet potatoes, are not reliably winter hardy in most of New England. So some gardeners dig them up each November and replant them each May.

But they take a long time to bloom unless you start them in pots indoors in April six weeks before the expected date of the last frost in your area. That’s around May 15 in most towns near Boston or the ocean, and Memorial Day in colder areas.

Not all varieties store well, so discard dried-up or moldy tubers and don’t buy that variety again. To multiply the survivors, cut each cluster of stems so each plantable, fingerlike tuber has at least one tiny eye bump or a bit of stem attached. The size of the tuber doesn’t matter. You should get several plantable pieces from each cluster.

If you order new dahlias, which are expensive, you’ll get single pieces, and you should start these inside, too. Fill individual 5- to 8-inch plastic pots two-thirds full with potting soil and cover a horizontally positioned tuber with 2 more inches of mix. Label and water thoroughly.

I do this in a dark basement because the tubers don’t need light until they sprout, at which point I water them again. I move the pots outside to a warm sunny spot in mid-May, but I don’t plant them for a couple more weeks because the soil is still cold and I can move the pots indoors if temperatures below 50 degrees are predicted. If the dahlias get too big in the pot, I pinch out the center stem, which can make them bushier and more productive.