The easy way to plant and care for dahlias: 10 tips

by Vasanthi Vasudevan

Blooming abundantly in a riot of colours from mid-July to first frost, dahlias are beloved by both experienced landscapers and novice gardeners. Bring drama to your landscape with these 10 tips to plant and care for dahlias in your garden. [Image credit: iStock.com/LianeM]

With dahlias, as with so many things, “well begun is half done.” You should begin by choosing the right place to plant dahlias in your garden. Dahlias need six to eight hours of bright sunlight per day to reach their full potential. The ideal spot would get plenty of morning sun and some shade in the afternoon.

Choose the smaller dahlias for window boxes and borders; choose mid-size dahlias for the interior of flower beds; choose the large, “dinnerplate dahlias” for the back of the flowerbed where you can set up unobtrusive stakes or supports. Once you’ve made your choice of flower and place, follow these 10 tips to fill your garden with colour.

1. Get a head start: Start your dahlias with tubers instead of seeds. Seeds generally don’t produce robust flowers and tubers for at least a year or two. Moreover, flowers from dahlia seeds tend to vary from the photo on the cover of the seed packet. For these reasons, breeders and landscapers prefer to start their plants with tubers.
2. Avoid cold feet: Give the soil a chance to warm up before you plant the tubers. Dahlias don’t do well if the soil is cold. Some gardeners, unwilling to wait for the eight weeks it takes for dahlias to begin flowering after planting,  jump start their dahlias by planting tubers in pots indoors a month before they plant them in the garden.
3. Look up: Plant the dahlia tubers with the “eye” facing upward. Don’t cut or break the tubers. Create a hole six to eight inches deep so that the crown of the tuber just peeks over the top of the soil.
4. Keep it light: Dahlias like a slightly acidic soil that is well-drained. When the tuber is planted, lighten the soil with bone meal, peat moss and compost before refilling the hole. No fertilizer is necessary at this point, although fertilizing with a low-nitrogen fertilizer in about 30 days will help flowering.
5. Don’t make waves: Do NOT water immediately after planting; wait until the sprouts begin to emerge before watering. When you do water, water the bottom of the plant rather than dousing the flowers and foliage. Do not overwater as this will cause the bulb to rot.
6. Bug off: Use repellant or bait to keep slugs and snails away from the tender young plants. Planting some companion plants such as rosemary, cilantro and thyme will help repel many kinds of insects; you can also try organic pest control methods. Once the plant is established and growing, prune the bottom leaves of the dahlia plant itself and direct your watering to the bottom of the plant to wash off mites and other insects.
7. Just a pinch: You can encourage healthy, bushy growth on smaller dahlias by counting up three sets of leaves from the bottom and pinching off the center shoot just above that point. This will produce more lateral branches and flowers. You can also do this on larger dahlias, once they reach about 12 inches in height.
8. Size up: To produce larger flowers on tall dahlias, pinch off all but the center bud of the typical groups of three buds on the branch.
9. Dead end: Pinching off dead flowers and foliage will keep your flowerbed looking tidy and encourage your dahlias to bloom more.
10. Chill out: Once the first frost forces tubers into dormancy, trim the plants to about 4 inches in height; dig up the clumps and shake the soil off. Inspect for and remove any wrinkled, rotten tubers and let the rest dry naturally. Once dry, then can be packed in loose sand or vermiculite and stored in a cool, dry, well-ventilated place. In spring, you can separate the tubers from the clump and plant them again.

Planning your garden can help you weather a long, cold winter. Check out more great YP gardening content to help you turn your thumb green, with many handy references on landscaping and lawn care. Want professional advice? Use our search engine to find professional landscapers near you!