How to Start Tubers in the Spring

April 29, 2016

By: Ashleigh Bliss

Like potatoes and unlike most flowers, dahlias grow from tubers. The tuber stores nutrients and energy over the winter, ready to put both to use to grow a new plant in spring.

Trouble is, our climate is notoriously cold, so that if planted directly into the soil, the tubers barely have enough time to mature into new plants before frost cuts the flowering season short. That’s why, come mid-April, gardeners routinely give their tubers a head start by stimulating the tubers indoors, so that the plants are well on their way by the time planting season heats up in late May. Here’s how they do it:

Start with last year’s tangled cluster of tubers and roots (See below), having been stored indoors all winter. The “mother” tuber—the one you planted in the soil last spring—will still be there: it’s probably the largest and its skin is noticeably tougher than the newer ones.

The first task is to separate the big clump into smaller, manageably sized tubers. At a glance, it looks like all you do is just snap them off, but in fact, it’s a job that requires a lot of cutting and slicing, not to mention a strong arm. And not all the new tubers are viable. Like potatoes, the good ones have “eyes,” a little pimple or nodule from which this year’s plant will grow. (See Below) Unlike potatoes, however, the eyes aren’t all that obvious and are easy to overlook until they sprout. Once you’ve found them, circle each eye with a pen

Start by cutting off any remaining roots and the smallest tubers with garden pruners (See below). Slice off the mother tuber and discard it. (If planted, it will probably grow again, but we’re told it is unlikely to flower.) Use a wide, curved blade if necessary and use Japanese shears for the finer snips. Sometimes, the tubers will break apart conveniently; more likely, it’s a bit of a chore.

When you’re done, you’ll have more waste than salvage, but you’ll likely have three or four, maybe even five or six new tubers per cluster, ready for planting this year (See below). It’s like free flowers!

Using an artist’s paintbrush, apply sulphur to the cut surfaces to inhibit mould (See below).

Plant the tuber in a small flower pot, about 5¼” in diameter. Use potting mix. The soil should be moist to the touch, but not wet. Keep the eye above soil level. (See below)

Place the pot under a grow light (See below) and with the right heat and humidity, the eye should sprout within a few days. It will grow faster if you can place the pot outdoors in the sun on warm days. Bring the seedlings in at night. The temperature should never go below 12°C and of course, do not expose the plant to frost, ever.

The plant is ready for the garden once it has several true leaves (See below) and there is no risk of frost for the reason of the growing season.


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