As regular readers of this column will know, I'm an enormous fan of dahlias.
They're the most prolific cut flower I know, and they bloom for months on end. A few tubers planted in your garden will keep your vase filled for at least five months.
But I won't waffle on any more about the virtues of this great plant, again. Suffice to say, if dahlias are one of your favourite blooms, now's the time to produce early cuttings to increase your stock.
It's easy to grow new dahlias from cuttings and it means you can quickly build up your numbers from a single tuber. If you plant one tuber out in the garden you will get one plant, but if you force a tuber to send up shoots in early spring, you can remove those shoots, pot them up and have between five and 10 new plants.
Stem cuttings can also be taken from 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, from which a number of cuttings can be taken.
Plant your tubers in pots in a mixture of lightly moistened sand, peat and potting mix. Leave the neck exposed, about 3 centimetres to 4cm, so that it's easy to take cuttings. Place the pots in a warm spot with good light.
If you have access to florescent lights you can place them beneath these. If you place your pots in a cool room, such as a garage, then bottom heat may be necessary. Use a heating pad or place on top of a fridge, or somewhere that you may get free heat.
After a while, shoots will appear. The time taken depends on the variety, although even tubers of the same variety may send up shoots at different times. Some may emerge within two weeks, others may take four weeks.
When the shoots are 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.
Remove the lower leaves from each cutting. If the remaining leaves are large, cut them in half to prevent the cutting from drying out. Pinch out the growing tip to encourage the cuttings to form roots.
Neatly trim the base of the cutting to remove untidy ends if necessary, then dip the cut end in rooting hormone. Insert cuttings in moist, free-draining potting mix. A 10cm pot will take four or five cuttings, placed around the edge.
Water the cuttings and place a plastic bag over the pot and secure it with a rubber band. A couple of short stakes 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.
In a warm spot, roots should form in about three or four weeks. At this stage, they can be potted into individual containers and grown on for a few more weeks. Keep pots in a warm, light spot.
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 re-pot once more before planting out.
Another means of propagating dahlias is by dividing the tubers. The best time to do this is once you've dug them up after the flowers die down in autumn. At this time they are soft and easy to cut. However, it's not so easy to see the eyes at this time, so if you do have trouble locating them, leave it until spring.
Bear in mind that the tubers themselves won't produce new buds. You must make sure that each tuber already has an eye on it for it to produce growth. The eyes are located on the swollen part of the tuber that attaches to the main stalk. Not all tubers will have eyes.
Use a sharp pair of scissors or secateurs to divide tubers, making sure there is at least one eye on each division. Discard any damaged tubers. A tuber that grows out from another tuber will not produce growth, so discard these as well. Then trim off the feeder roots to tidy up the tubers.
If dividing in autumn, wash tubers and allow to dry completely before storing in a box with dry sawdust. The box should ideally be stored around 4-10 degrees Celsius. Plant them out again in September or October.
Tubers divided in spring can be planted out once the risk of frosts has passed.
Then come summer you can enjoy your increased stock of dahlia blooms without a single penny spent.
- © Fairfax NZ News