Dahlias do take some care, but almost any gardener can have healthy dahlias without too much fuss. Dahlia plants come in a wide variety of sizes and shapes. They range in height from 1 to 6 feet, and the flowers vary between 2 and 12 inches across. Dahlias flower in a wide range of colours, and they bloom from early summer until frost.
Find a sunny location. Dahlias prefer a place that has protection from strong winds, and they like to grow in fertile soil that is well-draining. The proper pH level of the soil is 6.0 to 6.5.
Dig up the location, adding 2 to 4 inches of organic matter to the soil, such as compost, pine bark or well-rotted manure. When you this is incorporated into the soil, add 0.907 to 1.81 Kilogram of 8-8-8 or 10-10-10 fertiliser per 100 square feet. If you have a smaller area, add 2 to 4 tbsp of fertiliser per square foot.
Dig a hole that is 8 to 10 inches deep and a little wider than the tuber you are going to plant. To measure the hole, simply lay the tuber in the hole horizontally. With your trowel or shovel, loosen the soil at the bottom of the hole at least 6 more inches, but do not remove the soil. Refill the hole with the amended soil to a depth of 6 inches.
Place the tuber into the hole on its side, with the eyes facing upwards. Cover the tuber with 2 to 3 inches of soil. As the tuber grows, fill in the hole so it becomes even with the rest of the ground. If your dahlias are the tall variety, place a stake at the side of each dahlia hole, so the stake is ready to tie your dahlia to when it becomes taller. For spacing between each plant, consult the package directions of your particular variety of dahlia.
Add 3 to 4 inches of mulch around the dahlia flowers as they grow. This will keep weeds from growing and hold moisture in the soil.
Water your dahlias. Dahlias are heavy drinkers, so the soil needs to stay moist but not soggy. Keeping the soil too wet will cause the tubers to rot.
Pinch the stems back at the terminal bud when the dahlias reach 3 to 4 inches. You can find the terminal bud just above the second set of leaves. This will give your dahlia plant two main stems.
Fertilise the dahlias every month with a water-soluble fertiliser. Do not use a fertiliser that is high in nitrogen. Too much nitrogen will give your dahlias an abundance of leaves but very few flowers.
Remove the flower buds that appear on each side of the leader bloom. Dahlias bloom with three buds in a row. Leaving the middle bloom, pinch off the other two at the base of the leaf axil. This will give you a bigger flower. If you have the types of dahlias with smaller flowers, do not remove the blooms.
Dig the dahlia tubers out of the ground if you live in a zone below 8. Wait until after the first killing frost, and cut the foliage back so it is 2 to 4 inches above the ground. Begin digging at least a foot away from the centre of the plant to prevent spearing the tuber root. Gently brush the soil off the tubers.
Place the tubers on a screen for proper ventilation. Leave the tubers to cure in a shady place for 2 to 3 days.
Pack the tubers upside down in a ventilated box. Cover the tubers with vermiculite, perlite or peat moss that you have dampened with water. Store the tubers in a place that stays between 1.67 and 10 degrees C.
If the tubers are large, plant them two weeks before the last expected frost date. If the tubers are small, plant when all danger of frost is past. Check the tubers during their winter storage. If they are shrivelling, spray them lightly with water. If eyes on the dahlia tuber are not evident, simply place the tubers in moist leaf mould, peat, or soilless mix. A week or two later, the eyes on the tubers will appear