Dahlias have been slow to get into their stride this summer because of the chilly weather and those frequent showers. Large border dahlias love plenty of moisture but they tend to grow a lot of stems and leaves at the expense of flowers. Sunny weather and higher temperatures bring on flowers early and keep flowering going later in autumn. This is not surprising for a plant that originated in sunny Mexico.
While dahlias generally start to flower from late July or early August, they really look their best in early autumn. The vividly-coloured flowers seem to glow in the softer autumn light. There is an extraordinary range of colours - everything from pink to deepest red-black, yellow to dark orange, purple and white - but no true blue. Rich pink, dark red, smouldering orange and bright yellow are good for autumn as these colours resonate with the changing colours of the season. Planted among shrubs and perennials, they are invaluable for the lift they give to their surroundings late in the year.
Apart from the huge colour range, dahlias have been bred in a staggering variety of flower shapes and sizes. The original flower was a simple daisy-type flower with a ring of petals and a flat round dark centre. Now, apart from single-flowered kinds, there are anemone-flowered, collarette, water lily, ball, pompon, cactus-flowered and semi-cactus flowered, among others recognised for show purposes. A feast of rich colour is to be expected if the weather warms up a little. Border dahlias are very fast-growing, making a big plant in just a few months, so they like good fertile soil and lots of organic matter and they need good shelter. Staking is usually necessary.
Dahlias are prone to frost damage and the first really hard frost of the winter blackens the foliage and brings flowering to an end overnight. In mild areas it is possible to leave the tubers in the ground over winter without frost damage. Exposed tubers or tubers very close to the surface are easily killed. If loose compost or soil is placed over them, there should be no problem even in quite cold districts. But the tubers can rot in heavy soil and drainage must be good.
The emerging new shoots are frequently subject to snail damage in spring and this may result in the loss of tubers. To be safe, tubers can be lifted after the first frosts and stored in a cool, frost-free shed. The tubers are potted up in spring and started into growth, ideally in a greenhouse.
"I planted a hydrangea in early summer and it was thriving for the first 6-8 weeks but now some of the leaves are looking burnt and a bit dried out. More distressingly, all the flowers are fading in colour and turning brown. The soil is moist. I'm sure it doesn't need water but I have no idea what is happening to it." M O'Neill, Co Kerry
The plant may not have rooted away from the root-ball yet and has not settled in at the root. Therefore its capacity for growth is reduced. Also the plant may be growing in a more exposed position than it was used to and has taken some hardship, but it will adapt. The flowers are first to go when a plant is struggling, fading and turning brown. Give it a feed of shrub fertiliser in spring.