Dahlias and vegetable gardens have gone hand-in-hand for many years and the bright, bold blooms of these tuberous rooted perennials still have much to add to our gardens today. Their flowers are a late summer and autumn beacon for honey bees and beneficial predatory insects. In addition, their roots exude chemicals that are said to suppress and deter microscopic worms that attack vegetable plants. The sky is the limit when it comes to colour – dahlias come in yellows, oranges, pinks, reds, purples, lilac, white, bronze and multi-coloured. There are 10 recognised groups that describe the differing dahlia flower shapes. You can choose from flowers that are simple and open faced, double flowers – with layers of petals, tight and compact rounded flowers and bizarre cactus-like flowers that are spiny-looking and complex – almost other-worldly. The size of flowers ranges from the diminutive ‘lolipop’ to the huge ‘dinner plate’. Dahlias are so varied and at times dramatic they can become a bit of an obsession – you have been warned!
Dahlias are planted as tubers. Tubers are effectively a bunch of fat finger-like roots with an upward-pointing growing stem in the middle. Tubers can be ordered from suppliers in the autumn or purchased from garden centres in the spring.
Companions Plant with cleome, echinacea. sun flowers.
Plant tubers in early spring and summer countrywide when all risk of frosts has passed.
Dahlias grow best in full sun but if all you have is partial shade then they are still worth a go. They can be planted around the fringes of your vegetable garden as well as sporadically amongst beds where space permits. Smaller growing varieties can also be grown in pots. Plants can tend to have brittle stems so shelter from wind where possible.
Dahlias prefer a reasonably rich, well-drained soil. They do grow on most soils, however their tubers may rot in persistently damp and poorly-drained soils. If your soil is sticky then dig in coarse sand or fine pumice and organic compost to help improve drainage and soil structure.
Before planting dig a hole the size of a bucket and fill with well-rotted compost, rotted manure and some coarse sand or fine pumice to help with drainage. Mix together with garden soil. This can be done in the autumn to allow for ingredients to settle, combine and integrate with surrounding soil.
If you are in a cooler part of the country you can plant your tubers in pots of compost several weeks before you expect conditions to become warm and favourable for planting. This encourages tubers to start to shoot early – enabling you to get a head start on the growing season when they will be planted out in the garden.
When the weather has settled and is reliably warm and sunny, plant tubers at an average spacing of an arm’s length apart – this will vary from variety to variety so check growing dimensions for the varieties you choose.
First dig a hand deep hole in your pre-prepared planting spot. Make a shallow mound in the centre of your hole and sit the tuber on it with the upward-pointing stem in the middle and the fingers (if there are more than one) of the tuber radiating around it.
Cover the tuber with a thumb-deep layer of soil. Don’t water tubers at time of planting – this can cause them to rot. Now is the time to drive in a strong stake just outside the area of the tuber if your dahlia grows to more than knee height. (if you do this later when the plant has grown you might damage the tuber by accidentally driving a stake through it).
When shoots start to appear through the covering layer of soil you can start watering and then cover again with another thumb-deep layer and repeat until soil meets ground level.
Pinching out the growing tip when centre stem has three pairs of leaves will encourage branching and therefore more flowers.
Water once or twice per week during dry periods. If plants grow well they will need tying in to stakes for support in windy areas. Tie your string tightly to the stake and loosely around the dahlia stems – to prevent constriction and damage. Mulch around the base of your plants to keep soil cool and moist and to suppress weeds.
Flowers can be cut for use indoors. Use secateurs or a sharp knife to cut them off. Plunge straight into warm water before adding to your flower arrangement.
Dahlias can be left in the ground through winter in warm areas with free-draining soil that does not get water-logged in winter.Anywhere with damp soil or cold winters dahlia tubers should be carefully dug up in late autumn before frosts or the onset of wetter weather. Cut all stems back to about a finger’s length. Using a fork, go in about one and a half hands’ lengths from the centre of the plant. Ease the tuber from all sides to help loosen it. Gently lift the tuber from beneath. Wash off excess soil and allow tuber to dry before storing in a box filled with sawdust, wood shavings or fine pumice. The box should be stored in a dry frost-free place until the following spring when they can be planted out once again.