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Originally published Thursday, October 31, 2013 at 5:39 AM

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Putting pelargoniums to bed for winter, dividing dahlia tubers

Garden writer Ciscoe Morris gives advice on overwintering pelargoniums and dividing dahlia tubers.

Special to The Seattle Times

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In the Garden

One spring, a caller to my radio show shocked the living tweedle out of me. She told me that her entire collection of pelargoniums died after following my advice on overwintering them. I had told her to dig the plants and allow them to dry in a frost-free location before hanging them upside down in an unheated garage for the winter. Fortunately I had warned her that this is a risky proposition. If the plants freeze, get too warm or if the air is too moist or dry, it can end in disaster. The most foolproof way to overwinter any type of pelargonium is to pot it up and grow it as a houseplant by a window in a cool room with temperatures in the 50s. If you have lots of plants to overwinter, space restrictions may require you to hang them upside down. No matter how you overwinter them, take cuttings first. Pelargonium cuttings root easily in water. Next March, when the cuttings have substantial roots, pot them up in 4-inch pots using quality potting soil and keep them near a window or under grow lights in a cool room with temperatures in the 50-degree range. Water only when the soil surface feels dry, and fertilize every two weeks with soluble houseplant fertilizer, beginning with about half-strength dilution and increasing the dose slowly as spring temperatures rise. Put them outdoors on warm days, and pinch back the shoot tips to encourage bushy growth. You’ll have plenty of pelargoniums to plant out by Mother’s Day, and you won’t be as mad at me if your collection of mother plants ends up in the compost pile.

Divide your dahlia tubers now and then

I leave my dahlia tubers in the ground during winter. After cutting the plants back in fall, I cover the roots with an 8-inch deep cover of evergreen fern fronds. The fronds are great insulators and repel water, preventing the tubers from rotting in our cold, rainy winters. Although I’ve lost one or two in excessively cold winters, most survive year after year. Over time, however, dahlias left undivided for several years begin producing smaller, less spectacular flowers. That’s a sure sign the dahlia needs dividing. Dig up the rootstock in fall after the leaves and stems turn black. Tap off the soil and dry the clumps in a frost-free area for at least three days before beginning the dividing process. First, discard the original mother tuber and any broken, rotten or shriveled ones. Next, divide the rootstock, either into individual tubers or chunks containing several tubers. However you do it, make sure that the tubers in the division are attached to a stem from the previous year, as those are the only tubers that produce growth. Store the divisions in plastic grocery bags. Don’t add peat moss or any other substance. Tie the top of the bag, making sure there is plenty of air trapped in the bag with the tubers, which will maintain enough humidity to keep the tubers from drying and shriveling. Store the bagged tubers between 40-50 degrees. Untie the bag once per month, and if any tubers are shriveling, spritz them with water from a spray bottle. If any long stems emerge from the tubers in storage, snap them off right before replanting in mid-to-late April. Then start doing your push-ups. You’ll need strong arms to carry all those enormous dahlia flowers into the house for bouquets.

Ciscoe Morris: “Gardening With Ciscoe” airs at 10 a.m. Saturdays on KING 5.


About Ciscoe Morris

Ciscoe Morris' column runs Thursdays. His show "Gardening with Ciscoe" airs at 10 a.m. on Saturdays on King 5.

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