Q: SHOULD I CUT BACK MY DAHLIA?
A: Short answer, no.
Like all bulbs and tubers, Dahlias get their energy for the new season in the year prior to flowering.
Think of the tuber ( or bulb if you’re growing daffodils and Lily’s and such ) as a battery that powers the flowers. The leaves and stem act like the charging cord for the battery, if you cut them down then you are taking away its ability to store that energy, and the next season’s plants will be stunted, unhealthy with fewer blooms, and more prone to infection. Allow them to die off naturally, which usually occurs after the first frost has hit. If it’s really stressing you, you can remove up to but no more than 50 percent of the foliage with no ill effects.
Q. DO I KEEP FEEDING THEM?
A. no, reduce water and stop fertilizing them now. Spray for powdery mildew using a fungicide, whether homemade or purchased.
Q. When do I dig?
A. If you are digging up - not everyone needs to, it depends on personal choice and the conditions of your ground and climate- wait until the foliage has died off before digging out. I recommend using a garden fork instead of a shovel and gently loosening the soil in a two-foot radius around the clump, then lifting using the fork. I allow mine to dry with dirt attached as it helps protect them but you need to ensure they are DRY before storing as otherwise, they will rot. Dividing is done in spring once tubers are sprouting, as its almost impossible to see the eyes prior to this and without eyes, you won't get flowers. This is one reason why we DONT recommend buying tubers on TradeMe until October. Not only do you have to keep the tubers alive until spring, but a huge number of members received tubers that died due to being poorly divided or that had no eyes.
Q. How do I store them?
A. Again, depends on personal choice and the conditions of your climate. Some store in sawdust in containers in the garage, others place the clumps under trees and hedges, others wrap in glad wrap or newspaper. I've stored in open cardboard boxes in my garage before with no issues. The main requirements to successfully storing dahlia tubers for the winter is making sure they stay dry, have good air circulation, and are in a cool, dark spot.