Dahlias are warm-weather plants that grow best in a sunny, well-draining location. They thrive in warm weather and cannot tolerate frost, so you must plant them into warm soil well after all danger of frost has passed.
In cold climates, you can start your dahlias indoors about a month before your last predicted frost date.
Plant the tubers in one-gallon pots near a warm, sunny, south-facing window or under grow lights. Keep the soil lightly moist (not soggy).
The tubers may not sprout in this period but will develop roots. You can transplant them into your garden when there is no more danger of frost.
How Deep Should You Plant Dahlias?
Most dahlias should be planted at a depth of between 2″ and 4″ inches. However, you should dig the planting hole to a depth of 6″ to 12″ inches.
Then, fill the bottom couple of inches with a mix of native and light, airy soil well-amended with organic matter. Poorly draining soil can be amended with fine gravel to improve drainage.
Place the tubers on top of this layer of amended soil (1’ to 3’ feet apart) and then cover them with more of the amended soil.
Tamp it down lightly by hand, and add a layer of organic mulch over the top to help retain moisture and prevent weed growth.
You should see new growth within a month.
5 Tips For Dahlia Care During The Growing Season
1. If you are planting very tall, top-heavy varieties, such as Dinner Plate Dahlias, installing stakes when you plant is a good idea. In this way, you can be sure not to damage the tubers.
2. Throughout the growing season, you should provide a high phosphorus fertilizer to promote bloom production. Follow the packaging directions to feed your plants monthly.
3. Deadhead (or collect blooms for cut flower arrangements) throughout the growing season. This will help promote more abundant blooming.
4. Be sure to keep the soil evenly moist, never soggy, throughout the spring and summer. Then, reduce watering and cease fertilizing in the autumn.
5. At the end of autumn, after your first frost, you can cut back your dahlias’ foliage to a height of between 2” and 4” inches. Once this is done, you can prepare your tubers for the winter months ahead.
How Do You Prepare Dahlia Tubers For The Winter Months?
Because Dahlias are South American plants, they are only winter hardy in USDA hardiness zones 8 and higher.
However, if you live in zone 7, you can leave the tubers in the ground and give them a heavy layer of mulch to protect them against the cold.
In USDA hardiness zones below 7, you will need to carefully dig up your tubers and bring them indoors for the winter.
Place the tubers in a sheltered, dry location for several days to allow them to dry out. Once dry, brush excess soil off and store the tubers in baskets or other ventilated containers filled with slightly moist vermiculite, sand, or peat moss.
Place your baskets of dahlia tubers in a cool, dry place where the temperature will stay 45° to 55° degrees Fahrenheit throughout the winter.
Check on your tubers from time to time and remove any that show signs of rot.
Keep the packing medium very slightly moist by misting it with water occasionally. Always handle the tubers with care because they are quite delicate and can be damaged easily during this time of rest.
In the springtime, follow the directions provided above to plant your dahlia tubers into your garden after all danger of frost has passed.
How Do You Select The Right Dahlias For Your Setting?
Generally speaking, three broad groups of dahlias are divided into 10 classifications with many subcategories and distinctions.
Because there are so many choices, it’s a good bet that at least one variety is just right for your yard or garden.
Three Dahlia Categories
The largest dahlias can stand 3′ or 4′ feet high. The most popular of the large dahlias is the Dinner Plate variety. These stunning plants produce double blooms that may be a foot wide.
This sort of dahlia is a good backdrop for other tall, perennial blooming plants. They do well as a back border with a fence, trellis, or other support structure close at hand.
Dinner Plate dahlias present gorgeous, large blooms late in the summer and autumn.
These one or 2-foot-high plants are also a good choice as a border plant. In fact, medium dahlias are often commonly called “border dahlias.”
A blooming perennial bed with a back border of large dahlias and a front border of medium dahlias is a pretty sight. These plants combine especially well with asters and phlox, which also bloom late in the summertime.
Medium dahlias are also excellent container plants. They are large enough to put on a dramatic and impressive show but small enough to fit nicely into a large patio, porch, or poolside container.
If you have limited space but want to enjoy dahlias, small varieties that grow less than 2′ feet high are an excellent choice. These small dahlias can be successfully grown in planters, pots, and window boxes. They also make a nice border in flowerbeds planted with low-growing, blooming perennials or annuals.
No matter what size dahlia you choose to plant, you will have multiple choices in bloom characteristics.
All categories include varieties with either single or double blooms, with multiple subgroups within these varieties.