You may have ordered your dahlia tubers and potted them up, and by March and April they will have started sending up fresh green shoots. This is the perfect time to cut the new bottom shoots, called basal cuttings, and sprout them out. These free plants will flower in mid-July or early August, without damaging the original tuber you purchased. In fact, each tuber can produce about five new free plants, and if you have a warm place with bright light to keep the cuttings safe from the last frosts, you can enjoy a garden full of dahlias.
Start with a clean, sturdy seed tray. You can reuse the seed trays over and over again, but be sure to clean them with warm water and a little disinfectant between each use.
Fill the seed tray with all-purpose peat-free compost, take a firm, healthy dahlia tuber and place it over the compost, then add more compost around the tuber, but leave the crown exposed. You should be able to fit 2-3 tubers in a seed tray.
Water the compost thoroughly, either using an overhead watering can or by dipping the seed tray in a tub or sink of water and letting the compost soak up the water. When the surface of the compost is damp, remove it from the trough or sink.
Place the seed tray on a bright indoor windowsill or in a heated propagator. After a few weeks, new shoots will appear.
When they have reached about 10 cm in length, they are ready to be cut from the tuber. Take a clean, sanitized, sharp knife and cut as close as possible to where the shoot emerges from the tuber. If you can also attach a thin slice of tuber, this will greatly help with rooting.
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Insert the cutting with the powder, gel or honey glued into each module about 5 cm deep.
If you can’t find modular cell trays, use a 7cm or 9cm pot for each cutting instead. Close the cutting in the compost, cover with sand and water thoroughly.
Place in a heated propagator or cover the cutting and pot in a clear polythene bag to conserve water and place in a warm position with bright light, but no direct sunlight, such as an indoor windowsill facing east or west.
Check regularly and keep the cuttings moist but not soggy or waterlogged.
Gradually harden off new plants. This will take between a week and two weeks depending on the weather and dramatic temperature drops. Hardening off is simply acclimatizing the new plant from the inside out. If grown on a windowsill, open the window for a few hours each day.
You can also move the plants to a sheltered location for a few hours, extending the number of hours each day.
If you are using a cold frame, open it during the day and over a week increase the number of openings at night.
After a few weeks, they’re ready to plant in your borders or containers for a summer filled with dazzling dahlia delights.