How to Grow Dahlias
Dahlias are fantastic flowers as the images show which look great in the garden borders and as cut flowers in a vase. There is a huge range of colours and types but the drawback is that Dahlias require a good amount of time and attention and merit a red wheel barrow. Dahlias will flower from mid summer through till the autumn and the first frosts providing a long flowering season. Dahlias are like soil which is reasonably well drained, lots of sun and rich soil with lots of compost or manure. Dahlias originate from Mexico and Central America so it is no surprise that they survive and flower best in warm sunnier parts of the country.
How to Plant Dahlias
If you are planting Dahlias in leaf, as small plants, only do so when all risk of frost has passed as Dahlia are not hardy, (what does hardy mean?) and the growth will be damaged by frost. If planting Dahlias as tubers, this is best in May although you can plant Dahlias at any time provided the risk of frost will have passed about 6 weeks from your planting date, which is generally around late May depending where you garden in the UK. This is because it takes about 6 weeks for the plant growth to make it above the soil and the top growth is very frost sensitive. If you get caught out by a late frost place a cloche over the plant to protect it. When planting Dahlia as tubers they will need to go into a hole about 15cms deep having previously dug out the soil, added well rotted manure, and added blood fish and bone or your preferred fertiliser. Prepare the ground the same for ready plants, but plant more shallow with the pot soil level similar to ground level.
It is really important to be aware that Dahlias are not fully frost hardy for which reason at the end of the growing season, in all but the milder and sheltered parts of the UK, Dahlias need to be lifted and stored over winter. Dahlias do best planted in the more sheltered part of the garden and require full sun, a lack of sun can lead to poor flowering.
If your growing conditions are not ideal it is best to start tubers in a container and grow on under glass until around May when bring the container outside to harden off. This also makes it easier to lift the tubers for overwintering.
How to grow Dahlias
Once established and growing, to make plants bushy and produce more flowers when the Dahlia plant is grown to a good border height (depends on your border and variety say around 35cms) pinch out the growing tip which will make the plant throw out side shoots which will carry more blooms.
Another reason why Dahlias are a red wheelbarrow plant is that Dahlias need to be staked and to be tied in to provide support for the plant and blooms. It is best to get the stakes in before the plant gets too large, I nearly always leave it too late to stake plants and find myself trying to thread delicate shoots into the plant support. It is best to insert the canes around the plant as soon as growth begins.
Dead heading is essential throughout the entire summer to keep the plant flowering. Dahlias are prone to aphids and earwigs.
For the best blooms Dahlias need feeding, firstly about 4-6 weeks after planting with a feed high in nitrogen and potash and then regularly during the growing season.
Storing Dahlias over Winter
Dahlias are not frost hardy which means it is not generally advisable to leave the plants in the ground in all winter, unless the garden is in a very sheltered spot. It is advisable to lift the tubers in the Autumn. When the foliage has been blackened by the first autumn frosts, dig up and lift the plant, and then cut off the top growth, so you have just stem and tuber. Take care when digging up the tuber not to put the fork through the tuber or damage it as a cut or bruise can lead to rot when storing the tuber overwinter. Throughly clean off all clinging soil and this is usually best done by hand to ensure the tuber is clean for storage. Place the Dahlia in frost free place to dry out moisture retained in the tuber, which could take up to 3-4 weeks.
Once the tuber is fully dry, place the tuber in a box and cover the stem the vermiculite/sand/or dry compost to keep dry and frost free over the winter. Its a good ideal to label them. If you are lucky the Dahlia tubers will survive without mildew saving you the cost of buying them again next spring. Check them regularly and if any are showing signs of rotting discard. It is not unusual to loose some tubers over winter.
To make lifting Dahlias easier, you can grow them in containers and then when planting sink the container into the border. At the end of the season ens. Rather than dig up the individual tubers, the whole pot can be lifted out in Autumn.
There are many different types of Dahlia, classified by the shape of the flowers into 10 groups 2 of which are illustrated; left and centre Semi Cactus, and right Waterlily, as the images show the flowers are different shapes.
Dahlias are definitely a red wheel barrow plant. I have seen Dahlias described as "easy to grow" but in my book they are high maintenance. Ofcourse, it is often the case of "right plant right place", and in the more sheltered, warmer places in the UK Dahlia are easy to grow. Visiting the Cotswolds is such an example; marvellous Dahlias in abundance, flowering beautifully and no need to lift in the Autumn.