HOW TO PLANT AND GROW DAHLIAS
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Most Dahlias are bought in the spring as pre-pack sections of tubourous roots and these are very easy to deal with if you want to start them off early. If this is something you intend to do then do so no more than six weeks before planting out, but make sure that the threat of late spring frosts is over first.
Pot these root sections on into John Innes No.1 at a depth of about six inches - laying them down horizontally. Unlike most other plants it is important NOT to water them in - if you have done so by accident they will need to be placed into a warm environment for the compost to dry out, otherwise the tubers will rot. Label them and place them back into a cool but frost-free area and once the new growth begins to appear they can be moved on into a bright position - but not in direct sunlight - until the foliage has a chance to harden off. Then they can be planted outside into a free-draining soil located in a bright, sunny location . If you live in a hot Mediterranean climate then they will do better in just the morning sun preferring shade in the afternoon.
Unless you are growing miniature bedding varieties you will probably to need to stake your plants. Use 6ft canes and put them in the ground before planting your young plants to avoid damaging the new root growth. Short stakes can be used to start off with, but they may need to be replaced with taller ones later on. These can either be placed behind the originals or swapped over one by one. Once the new growth reaches about 8 inches high, nip out the growing tips. This will create a more stable plant by producing new growth from the lateral stems. Once this secondary growth gets to about a foot high you can look at tying them into the canes. This is repeated at every 1 foot of growth to prevent them from being blown over in poor weather. Resist applying fertilizer at this stage as this will produce too much leaf growth at the expense of flower production.
As plants near their flowering period you may wish to remove some of the juvenile flowering buds as this can improve flower size and stems. Feed your plants fortnightly with a high potash fertilizer as soon as your plants begin to flower as this will help with further flower initiation. It is also important to dead-head any flowers that are past their best to encourage the next generation of flower buds. If this isn't done the plant will form seed heads and stop flowering. Keep tying the plants in until the end of the season
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