There are a few important things to know when planting dahlia bulbs. First, they like warm soil, so check your region’s last frost date to ensure the ground isn’t too cold.
Plant the tubers at least 2 to 4 inches deep, and space them about 1 foot apart, depending on the variety. Dahlias with large flowers grow best when spaced wider.
Preparation
Unlike bulbs such as lilies, daffodils and tulips that can be planted in fall, dahlias require warm, well-drained soils for planting. Prepare the soil before planting by amending it with 2 to 4 inches of high-quality compost or aged manure, a light dusting of bone meal and a balanced organic fertilizer.
To plant, dig a hole that is about 4-6 inches deep. Place the tuber with its eye facing up and gently cover with soil.
After a few weeks, check the soil to see if any shoots have emerged above the ground. If they do, it’s time to move them outside into a sunny spot.
Dahlias are very easy to grow and reward gardeners with outstanding blooms year after year. But like other flowering plants, they also need a few tips to help them thrive.
Planting
If you’re growing dahlias from tubers, it’s a good idea to plant them in the spring. Dahlias like a warm soil and can be planted up to mid-June in most parts of the country.
When planting your bulbs, make sure they are well buried and that they’re at a depth of around 3-4 inches below the surface of the soil. Then, fill in the hole with soil and firm it in.
To prevent the plants from tipping over, you can also add a stout stake to each bulb when planting them outside. This is particularly important with tall varieties, such as dinnerplate dahlias, which can easily topple over in the wind.
If you’re storing your bulbs over winter, lift them once the foliage has blackened by frost and store them in a dry place away from direct sunlight. This will encourage them to re-shoot next year.
Watering
Once you’ve planted dahlias, water them regularly. They’re thirsty plants and need consistent watering to grow and develop properly.
Dahlias like a moist soil and don’t do well if they’re overwatered, so set up soaker hoses or drip irrigation to keep the soil damp throughout the growing season.
When you’re ready to plant your dahlia bulbs, dig a 6- to 8-inch deep hole and amend the soil with plenty of compost. If you’re planting on heavy clay, add some grit to the hole.
When dahlias are 1 foot tall, pinch out 3 to 4 inches of the center shoot to encourage low basal branching, which increases flower production and stem length. For large flowers, try disbudding: Remove the two smaller buds next to the central one in a flower cluster.
Fertilizing
One of the most important factors that determines dahlia plant health and blooms is the amount and type of fertilizer used. If you want your plants to thrive, it’s important to use a low nitrogen formula in the right amounts.
In order to stimulate flowering, your fertilizer should be rich in potassium and phosphorus. Potassium is the key to a thick, upright stem, while phosphorus promotes dense growth and strong color display.
The first step is to get a soil test to determine what nutrients your dahlia bulbs need. This will help you choose a formula that works best for your soil.
Harvesting
If you’re growing dahlias in a colder climate, you must dig up and store the tubers before the first frost. This can be done in the fall, before they’re killed by frost or as soon as they go dormant in the winter.
Once you’ve dug up all of the tubers, rinse them thoroughly and examine each clump to make sure that there aren’t any rotten pieces. Also check to make sure that each clump has at least one eye.
Once the clumps are clean and dry, you can place them in plastic bags or crates. Be sure to place them in a cool, dark place with good air circulation. Some gardeners use vermiculite, wood shavings or sand to keep the tubers from drying out.