Growing Dahlias
Planting
For best results, select a sunny well-drained location with at least six hours of direct sunlight. Prepare your soil with an application of compost or well-rotted manure and dig or till to a depth of six to eight inches. A balanced fertilizer like 10-10-10 or 6-12-12 may be added if manure is not available.
In Nova Scotia, the tubers could be planted from mid-May to early June, depending on where you live. If you are planting green plants, wait until the last frost in spring.
If starting a new garden, a light application of limestone should be applied as Nova Scotia soils are usually acidic in nature and dahlias like a slightly acid soil. A soil test from the Nova Scotia Department of Agriculture would helpful.
Supports
Dahlias need support due to their height. Four- to five-foot wooden stakes or rebar can be used. Space stakes every two feet apart for a single tuber or three to four feet apart and plant a tuber on each side of the stake. Drive stakes in before planting.
Dig a hole three to four inches deep, about two inches away from the stake to accommodate the tuber. If your soil is a heavier clay-type, then plant shallower, two to three inches deep.
Place the tuber in the hole horizontally with the shoot end two inches from the stake and the eye or shoot pointing upwards. Cover with soil but do not water in as the tuber does not like to be in saturated soil and the tuber itself will support early growth. After planting, growth should appear from ten days to two weeks. At this time, you can place a tomato cage over the plant and secure it to the stake using a nylon zip tie. The tomato cage eliminates having to tie the dahlia to the stake at intervals as the plant grows.
Disbudding
You may allow all flower buds to bloom if you wish but, if you want stronger stems with larger flowers, you need to do a procedure called “disbudding”. You remove the two side buds on each side of the main bud on the stem so that all the strength then goes into the one flower.
Autumn Harvesting and Storage
After a hard frost has blackened the dahlia foliage, wait four or five days before cutting the stalks back to four inches above the ground. This waiting period allows the dormant buds on the tubers to swell, making them easier to see and divide. Long-handled cutters work great for this job.
If it is an extra long season, your dahlia plants may be cut down while still green. Follow the same process as above.
Using a round-nose shovel, dig around the dahlia plant about five or six inches away from the plant and gently pry the clump up out of the soil. Gently shake the loose soil from the clump. If you are keeping track of the variety name, attach the name tag now.
Allow the clumps to dry on the lawn or clean surface for a few hours. Store the clump as is or it can be washed for storage.
Many growers split the clump in the fall because they are easier to cut apart in the fall rather than in spring. Always dispose of the old tuber as it is usually rotten in the centre. A sharp knife or pruners can be used for this job.
To divide the clump, cut a tuber from the main stalk making sure it has a viable eye or shoot. Allow the cut tubers to dry for a day to heal the wounds and then pack them away in vermiculite for winter storage. Store the tubers at a temperature of 45-55 degrees Fahrenheit or 8-12 degrees Celsius.
See our page on Overwintering Dahlia Tubers
A Few Tips
In most areas of Nova Scotia you can plant your tubers in the ground around May long weekend.
If you started your tubers in pots and have green plants you will have to wait until the risk of frost has passed in early June. Started plants will yield earlier blooms but require some extra care to grow a green plant.
Labeling your dahlias is always a good idea, but many markers are not waterproof and fade in the sun despite the fact they are advertised as UV resistant. The best marker is a plain old HB Pencil that will last for years. There are numerous materials that can be used for labels that do not get brittle in the sun but probably the best would be vinyl siding cut in narrow strips and a hole drilled or punched for a wire to attach it to the stake or tomato cage.
Dahlias as Cut Flowers
The main reason for growing dahlias is to brighten your garden with their fantastic blooms especially into the fall season, but dahlias are becoming hugely popular as a cut flower. The popularity of the dahlia is growing each year for weddings and anniversaries, but it is hard to come by quality blooms from florists so plan on growing your own.
When cutting blooms for interior use, it is best to cut early in the morning when the bloom has stored up food reserves during the night and are not overheated by the hot noon sun. The blooms need to be cut on a slant to allow for more uptake of water and a plant food can be added at this time. The blooms can be placed directly into a vase of clean water and displayed as required.
If the blooms are to be used in an arrangement or basket, then they need to be "hardened off" which is where the blooms are allowed to sit in water in a cool place for a few hours before sticking them in oasis floral foam for display. Be sure to add additional water to the oasis as the blooms will remove a fair bit of water over time from the oasis. If you practice disbudding as previously mentioned, you will have larger blooms and longer and sturdier stems for use in your arrangements.