How to get more dahlias for free: How to force tubers in winter

Buying dahlia tubers can be expensive, but here’s an easy way to increase your numbers.

Words: Jane Wrigglesworth

Love dahlias? Don’t like the ridiculous prices you can pay for tubers? Here’s how you can increase your stock by forcing tubers to produce early shoots. You can remove those shoots, pot them up and get 5-10 new plants.

Stem cuttings can also be taken from actively growing plants during summer, but you’ll get better results from tubers that are forced in winter. Ideally, use an established plant, as these will throw up more shoots than a young plant.

1. Plant your tubers in pots in a mixture of lightly moistened sand, peat and potting mix. Leave the neck exposed about 3-4cm so that it’s easy to take cuttings. Place the pots in a warm spot indoors with good light. Supplement with fluorescent lighting if necessary. Bottom heat works well too, although it’s not always necessary. You can use a heating pad if you have one, or try this compost method.

2. Shoots will emerge in 2-4 weeks. When about 7.5cm long, select strong, healthy shoots and sever them at the base, close to the crown of the tuber (but not cutting into it) with a clean, sharp knife. You can leave a few stems on your original plant to grow on.

3. Remove the lower leaves from each cutting. If the remaining leaves are large, cut them in half to reduce the amount of transpiration while the cuttings have no roots. Pinch out the growing tip too, to encourage the cuttings to form roots.

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Dip the ends of the cuttings in rooting hormone, then insert in moist, free-draining potting mix.

A 10cm pot will take four or five cuttings, placed around the edge.

4. Water the cuttings, then place a plastic bag over the pot and secure it with a rubber band. A couple of twigs inserted into the soil will stop the bag falling onto the cuttings. Leave the pot in a warm, light spot and invert the plastic bag daily to stop condensation building up.

5. In a warm spot, roots should form in about four weeks. At this stage they can be potted into individual containers and grown on for a few more weeks. When plants have formed four or more pairs of leaves, cut off the tip just above the third pair to encourage a bushy habit. You may need to repot once more before planting out in September or October.

NZ Lifestyle Block This article first appeared in NZ Lifestyle Block Magazine.
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