Dahlia Grow Guide

Storing the tubers once they arrive

If you need to store your tubers before you plant them out, I recommend using wood shavings or vermiculite (moist but on the dry side). Fill up a plastic container or box and put down a layer of the storage medium, then alternate tubers and more storage medium. Finish up the box so that the tubers have a layer of medium (wood shaving, etc.) covering them. Check on them every day or two and try and store them in a cool place that receives good air flow.

When to Plant

Many people say to plant your Dahlias the same time that you plant tomatoes. Typically an open, sunny location preferably on the Eastern side and sheltered from the western sun. They prefer morning sun and afternoon shade. You can plant Dahlias anytime from June to December depending on where you live. In subtropical or tropical climates, I recommend planting them at the beginning of September, after the risk of frost has passed. Dahlias also need 12 hours of direct sunlight to come out of dormancy. It typically takes 3-5 weeks for tubers to come out of dormancy.

How to Plant

Ensure your raised Dahlia beds are prepared with cow manure or compost and ensure you use drip line to water them to minimise tuber rot and disease (Dahlias have hollow stems which can catch water and cause rotting). Keep in mind that they prefer a slightly acidic soil (our soil is alkaline and they still grow well). Please place your stakes or steel pickets in the ground prior to planting them to avoid damaging tubers. They need strong support as the branches get very heavy and can snap off. Many people use flower netting or wire horticultural mesh to provide reliable support. Always plant Dahlia tubers with the eyes facing upwards. Make sure you sow them 7-10 cm deep and approximately 40cm apart in a raised bed nourished with good compost or cow manure. The tubers seem to grow better than when they are planted at this spacing distance. Always keep the soil moist but not drenched and aim to water deeply 2-3 times a week. Also, please do not plant your tubers if a week of rain is forecasted, try and wait until after the rain event to avoid rotting your tubers. If your Dahlias are planted in a full sun location you should definitely consider growing them under 30% white or beige shade cloth to minimise sunburn.

How to Maintain

After the plants have been planted in the ground, you can pinch out the Dahlia plants when they have 3 sets of leaves (20-30cm). Just pinch out the middle stem just above the third set of leaves. This is to encourage more branches (therefore more flowers). Once the plant is established, you can also disbud flower buds to get larger flowers by removing the two outside buds and leaving the central bud. Always remove every flower to encourage the plant not to go dormant by setting seed. To fertilise treat with a high nitrogen fertiliser(leaf growth) through the middle of season but restrict that towards the end. Seaweed applications are also beneficial to the soil microorganisms. If possible, cover crops over winter are also useful at replenishing nitrogen in the soil.

How to Dig Up and Divide

At the end of the season (April-June), it is time to cut the plant down by thirds and encourage it to go dormant (leave about 15cm-20cm of the stem). If you live in a warm climate you can leave them in the ground but run the risk of having difficult to divide tubers the following year. Use a pitchfork to gently loosen the soil around each plant. Once, you have pulled the plant up I recommend to leave the clumps of soil around the tubers (somewhere out of direct sunlight) and only wash the tubers when you are ready to divide. Make sure you leave the Dahlia stalk and tubers upside down to ensure all water drains away from the tubers. Next, you need to divide the tubers ensuring you leave a section of the main stem with each tuber which is where the eyes from. All healthy tubers need an eye, neck and body (or part of). Please note that the size of tubers is irrelevant, the smaller tubers are said to grow more quickly into a plant. There is an abundance of videos on Youtube or Facebook Dahlia groups on how to divide (we will create a how-to soon).

All the best with your Dahlia growing journey!

Anna xx