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Jessica Walliser

Give dahlias a head start to coax earlier blooming

Jessica Walliser
| Saturday, March 26, 2016, 6:00 p.m.
Dahlias typically bloom in mid- to late summer in Western Pennsylvania.
Jessica Walliser
Dahlias typically bloom in mid- to late summer in Western Pennsylvania.

If you love the gorgeous blooms of dahlias as much as I do, you'll do anything you can to see more of them. I'd like to share one of my favorite tricks aimed at encouraging earlier bloom production.

Dahlias grow from tuberous roots. They're winter-hardy in the South, but here in Pennsylvania we grow dahlias as an annual. Many gardeners dig the tubers up in the fall and store them in a peat-moss-filled cardboard box for the winter. Then, we replant the tubers into the garden as soon as the danger of frost has passed. When planted this way, most varieties won't produce blooms until mid- to late summer.

But, to grow dahlias that produce blooms four to six weeks earlier, instead of waiting to plant the tubers directly into the garden, give them a head start by planting them in pots and growing them indoors. You can do this with tubers you've overwintered yourself, or with new tubers purchased from your favorite garden center or mail order source.

Begin the process six to eight weeks before our last expected frost; around here, that's anytime between March 15 and 31 (our last expected frost date is around May 15).

You'll need an 8-inch-diameter pot with a drainage hole for each dahlia tuber and enough high-quality potting soil to fill all the containers. Fill the pots with potting soil about three-quarters of the way, then position one dahlia tuber on top of the soil in each pot. Make sure the growth nodes are pointing up. Then, fill the pots to the top with more potting soil.

The top of each tuber should be about two inches below the soil line. Water the pots well, but do not allow the base of the container to sit in standing water, as doing so could lead to rot.

Place the containers in a bright window or under grow lights. Ideally, they should receive a minimum of eight hours' sun per day. Water the containers regularly, and do not allow them to dry out completely.

In one to two weeks, you'll see dahlia sprouts poking out of the soil. For even growth, turn the pot one-quarter turn every day to expose all sides of the plant to an even amount of light.

When the danger of frost has passed, transplant the sprouted dahlias into the garden, locating them where they will receive full sun. Be very careful when handling the sprouted tubers so you don't break off any of the new shoots. Give each plant plenty of room to grow, and provide some sort of stake or trellis to encourage strong, upright growth and keep the plant from flopping onto the ground.

By starting dahlia tubers indoors a few weeks in advance of outdoor planting, you'll see earlier blooms and a longer flowering season. I don't know a single gardener who wouldn't want that!

Horticulturist/author Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. Her website is jessicawalliser.com.

Send your gardening or landscaping questions to tribliving@tribweb.com or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.

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