So far (and the weather may yet change things) 2019 is proving to be a great year for Dahlias. The warm weather has brought a flush of flowers with excellent colour in the petals. We are often asked the “secret to success” with these plants and, to be honest, we find the two main keys to good flowers are watering and feeding.
Dahlias are fleshy plants, so they rely on a good supply of water to keep the stems upright. If moisture is in short supply, it is channelled into keeping the plant stems and leaves first, then into the flowers later if there is any left over. In pots, this means checking them at least once a day. (Below: Dahlia 'Cafe au Lait')
They are also quick-growers once they get going, so they quickly exhaust the food near the roots. Controlled-release fertiliser helps with this and you can add a supplementary boost of tomato food once a week as the buds form and the blooms open.
Pot size is also important because the smaller the volume of compost, the less water it will hold and the quicker it will be used up. Dry pots are unstable and you will find they blow over easily in the wind. Larger pots are easier when it comes to staking the plant, too.
In the border, slugs and snails may prove problematic and will need dealing with. If you plant a Dahlia and wonder why you never see any shoots, it’s probably because they are being grazed off as fast as they appear. (Below: Dahlia 'Creme de Cognac')
The question of lifting the tubers in winter is one that causes lively debate between gardeners, with some who favour lifting and others who leave them in place. We find it depends on the soil. Tubers in a light, quick-draining soil are likely to be fine over winter, especially if you pack some straw into a wire hanging basket and invert it over the top of the tuber to keep the frost off. Tubers in a heavy damp soil may rot off in a wet winter and are usually best lifted.
Wait until the frost has blackened the stems, then cut the plant down and lift gently with a garden fork. The remaining stems will contain moisture, so leave them upside down somewhere dry (greenhouse, shed or garage) to drain for a few days. Once they have dried, they can be packed into a seed tray or similar with some wood shavings, compost or newspaper around the roots. Store them in a dry, frost-free place over winter and then start them back into growth by potting into fresh compost in late January in a frost-free greenhouse or frame. This might sound early, but you can often harvest a good crop of cuttings from these early shoots and increase your stock of plants.
(Below: Dahlia 'Creme de Cassis')
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