When To Plant Dahlias: How Late Can You Plant Dahlia Tubers?

Summer would be incomplete without dahlias. These beautiful flowers bloom in almost every color imaginable, ranging from hot, vibrant shades to stunning, pale pastels. They add color to your lawn during the late summer months and complement every garden style, whether it’s a cottage-style border or a lush, exotic scheme. But when’s the right time to plant dahlias? 

It’s better to plant dahlia tubers in spring, specifically in the months of April and May. If you live in a warmer area, you can start planting a bit earlier. You can also plant the tubers indoors in March and then transplant them to your garden in spring for faster results.  

Understanding when and how to plant dahlias correctly will help ensure a magnificent show of flowers. However, with the flower existing in so many different colors and forms, it can be difficult to determine the right planting time. Let’s look at the ideal time to plant dahlias, the proper planting and growing process, the best companion plants for dahlias, and how to safely store them during the winter. 

What Is the Best Month to Plant Dahlias? 

Gardener planting flowers in the garden

It’s best to plant dahlia seeds (on Amazon) during spring when the soil is still warm and there’s little to no chance of frost. If you also grow vegetables, then you can simply plant dahlias with the tomatoes. 

In many places, spring falls from April to May. However, if you live in a warmer climate, you may need to start the process a bit earlier. If you’re experiencing or expecting a lot of rain during these months, then it’s best to wait for clearer skies. 

If you want your dahlias to bloom as early as possible, you can start planting the tubers indoors about a month before the actual outdoor planting time. By starting early, you’ll have a small plant you can transplant as soon as spring starts.  

However, don’t rush the process. While it’s tempting to have a garden filled with growing dahlias even before spring starts, it’s best to wait until the soil has properly thawed and there’s no risk of frost.

Also, make sure the ground temperature is at least 60˚F, or 15˚C, before planting. It’s advisable to consult the USDA Plant Hardiness Zone Map as well, and then plan accordingly.

How to Plant Dahlias

To help ensure you have a vibrant and breathtaking flower bed, here are a few tips on how to plant dahlias:

  1. Don’t plant dahlia tubers that look rotten or wrinkled. Pink buds or “eyes” and a few green sprouts are good signs. 
  2. Dig a six- to eight-inch deep hole for the tubers. 
  3. Place a dahlia tuber into the ground, with the eyes or growing points facing upwards. Don’t cut or break individual tubers. This should only be done if you’re planting potatoes.  
  4. Cover each tuber with around two to three inches of soil. 
  5. Once the stem sprouts, fill the hole with soil until it’s at ground level. 
  6. Don’t water the tubers immediately after planting, as this can lead to rot. Instead, use your watering can after the sprouts appear above the soil.
  7. Make sure the planting hole is slightly bigger than the plant’s root ball, and add a bit of sphagnum peat moss or compost into the soil. It’s also advisable to mix some bone meal into the soil. 

Should You Soak Tubers Before Planting? 

You don’t need to soak the tubers before planting. However, there’s no hard and fast rule on the matter. In fact, some gardeners soak dahlia tubers to rehydrate them after winter storage. 

Soaking dahlia tubers before placing them in pots will also speed up and stimulate the growing process. It’s advisable to soak them in lukewarm water for around an hour before you start the planting process to ensure proper rehydration. 

However, after the initial soaking and watering, make sure you don’t over-water the plant. It’s best to wait until the soil has almost dried up before picking up your garden hose again. Dahlia tubers will not dry out, but they might decay or rot if the soil is too damp for the roots to spread and get a good start. 

Can You Plant Dahlias Straight Into the Ground?

While you can plant dahlia tubers straight into the ground, it’s first important to create the right environment for the plant to grow. 

Dahlias thrive under full sun and in well-drained, fertile soil. To ensure a vibrant, colorful flower bed, it’s a good idea to mix organic or compost matter into the soil before planting the tubers. You can also add an all-purpose granular fertilizer (on Amazon) for the larger plants and bigger blooms. 

Make sure you plant dahlia tubers, with the eye (the point from which the flower grows) or bud facing upwards. Place them at least three to four inches deep into the soil and keep each tuber about 12-18 inches apart. 

However, keep in mind that the distance between each tuber varies with the type of dahlia you plant. Larger flowers might need as much as 30 inches of space between each tuber, so make sure you consider the ultimate size of your selected variety. 

Before you cover the tubers with soil, insert a stake or any other type of plant support to avoid damaging the tubers in the future. Most dahlias grow up to five feet tall, and adding a stake can actually help protect the stems from the wind.  

Lastly, fill the planting hole with soil, pack it in, and give the plant a good watering. Don’t water again until you see green shoots, or the plant could rot. 

Your dahlias should sprout within a couple of weeks. Once they’re about eight to twelve inches tall and have at least three pairs of leaves, remove or pinch out all the growing tips. This will encourage branching and help ensure a healthier plant with more dahlias. 

To do this, you just need to use sharp, clean pruners and cut around 3-4 inches above a pair of leaves.

How Deep Should Dahlias Be Planted? 

Large-growing dahlia tubers should be planted around six inches deep, while it’s better to plant smaller-growing ones four inches deep into the soil. If you’re planting them in pots, cover the tubers with around one to two inches of potting mix (on Amazon)

If your dahlia will reach more than two feet above the ground, insert a stake into the planting hole and place the tuber about two inches away from the stake. This way, you won’t have to worry about damaging the tuber by adding a stake in the future. 

How Much Space Do You Need Between Dahlias?

Dahlias need a lot of room to grow, so make sure you plant each tuber about 12-18 inches apart. As we mentioned above, this varies depending on the type of dahlia. It’s advisable to plant larger dahlias in a separate plot where they won’t have to compete with other plants. 

Plant the tubers in rows and leave around 3 feet of space between each one. If you want a flowering hedge, plant the dahlias about one foot apart, so they can support each other. 

It’s better to plant low- to medium-height dahlias that grow up to three feet tall with other summer flowers.      

Unless your dahlia is of a dwarf variety, you’ll need to add some support after planting them. Dahlias grow incredibly fast and tend to flop, especially if they have large flower heads. To avoid this problem, add bamboo canes or stakes at all four corners and tie in any new growth every few weeks.

How to Grow Dahlias

Once you’ve successfully planted your dahlias, you’ll need to water them two or three times a week. You may need to use your garden hose even more frequently if you live in a hot, dry climate. 

It’s also important to tend to the flowers before and after rain, as the wind can damage the fragile stems. Large, open blooms fill up with rain water, so make sure you empty them out as well. 

Here are a few more tips that can help ensure healthy and steady growth:

  • Dahlias bloom approximately eight weeks after planting, generally in mid-July. 
  • Occasionally apply low-nitrogen, liquid fertilizer, like 10-20-20 or 5-10-10, to promote healthy growth. Fertilize after you see sprouts, and then every three to four weeks, from midsummer to early autumn. However, make sure you don’t over-fertilize, as this can lead to weak tubers, small or no flowers, or rot. 
  • Add a high potash feed, like tomato feed (on Amazon), to the soil every fortnight. This will help ensure the flowers keep coming. 
  • When your dahlias grow up to 1 foot tall, remove or pinch out three to four inches of the middle branch. This will help encourage leafier plants and improve stem length and stem count. 
  • It’s better to disbud larger flowers. If you have a flower cluster, keep the central bud and remove the smaller ones next to it. This way, the plant will push all its energy and nutrients into growing fewer, but considerably bigger dahlias. 
  • You don’t need to stake or disbud bedding dahlias. Just pinch out the middle or center shoot above the third pair of leaves to promote growth. 
  • Deadhead the flowers as they fade to encourage more blooms.
  • Don’t mulch the plants, as dahlias love feeling the sunlight on their roots. 
  • For taller plants, it’s better to add stakes when you’re planting them. It’s also advisable to moderately disbranch, deadhead, pinch, or disbud the flowers for three months or more to produce a lovely, showy display.  
  • If you’re growing dahlias as cut flowers, cut them only when they’re fully open.
  • Dahlias are incredibly hardy in areas warmer than USDA Hardiness Zone 8, so you can simply cut them back and leave them in the soil to overwinter. However, make sure you cover the plant with a dry, deep mulch. 
  • If you live in colder climates, then it’s better to lift and store the tuberous roots during winters. Keep in mind that the flowers can survive in Zone 7 and even Zone 6 if the cold isn’t too harsh. 

What Grows Well With Dahlias? 

Dahlia flowers in the garden

Dahlias are perennials, so it’s better to plant them in a mixed perennial bed. However, make sure you consider the water needs of each plant before planting it with dahlias. 

It’s better to choose plants that repel pests, so you don’t have to worry about any insects damaging your flowers. Herbs are an excellent choice, as most of them release pungent oils and scents that deter pests. 

Here are a few herbs you can plant with your dahlias:

  • Artemisia has beautiful, finely-cut silvery foliage that repels slugs and perfectly sets off the delicate, lacy foliage of dahlias. 
  • Creeping comfrey survives in light shade and might also deter slugs.
  • Anise and coriander are ideal companion plants if you’re planting your dahlias in the kitchen garden. Coriander repels aphids, while anise attracts predatory wasps that kill pests. 
  • Thyme, rosemary, and mint are excellent herbal companions as well. 

You can also plant perennials and annuals together in a dahlia bed:

  • Nasturtiums are riotous growers with repellant properties and bright, colorful blooms. The spicy flowers are edible as well.
  • Flowering sage, or salvia, boasts bright, colorful spikes, which attract pollinators, like moths and butterflies. 
  • Similarly, bee balm, or Monarda, brings bees to the flowers.
  • Geraniums don’t have a pleasant smell, but they’re toxic to aphids. This means that they can protect your dahlias from many pest-related diseases.
  • Try planting old-fashioned bloomers, such as peony, lilies, and roses, with your dahlias for ageless elegance.  

Before you plant any companion plants, make sure you consider their size. Since most dahlias form large bushes, bigger and taller plants will compliment your flowers nicely if you install them as a backdrop.

  • Towering butterfly bush, agapanthus, and joe pye weed are beautiful vertical choices that will brighten up your entire garden. 
  • Sunflowers also grow as tall as dahlias and will bloom beautifully in the same flowerbed, so you can add their cheery faces to increase your garden’s charm. Marguerite daisies, goldenrod, and helenium are other tall plants that can add height. 
  • Lastly, you can plant annuals, like marigold, bacopa, ageratum, and petunia, in front of the dahlia tubers to add more color and bring the whole effect together. 

How Do You Winterize Dahlias? 

If you live in a colder climate (USDA Hardiness Zone 7 or colder), you’ll have to winterize dahlias and dig them up in the late fall. 

It’s very easy to dig and store dahlias in the winter. Winterizing them will also save you money in the long run, as you won’t need to purchase new tubers every year. 

Here are a few tips on winterizing dahlias: 

  • If you live in a colder region, then it’s advisable to dig up and store the tuberous roots as soon as winter starts. 
  • While some gardeners claim that dahlias can survive Zone 7 temperatures if the cold isn’t too harsh, leaving the plants in the ground is still risky. If you live in Zone 6 or somewhere colder, it’s better to dig up your dahlia tubers. 
  • Don’t dig the tubers until the first hard frost kills all the top growth. It’s advisable to check the fall frost dates for your area, so you have an idea of when to start digging. 
  • Dahlia foliage turns black after the first frost. Once this happens, start digging up or lifting dahlias. Make sure you complete the process before the arrival of a hard frost. 
  • Cut dahlia stems right before you start digging. This is because dahlias have hollow stems, and any water collected in them can lead to tuber decay and crown rot. 
  • Remove blackened foliage and leave only two to four inches of top growth.
  • Use a garden fork, shovel, or pitchfork to dig around the tubers. It’s advisable to keep a gentle hand, as the “neck” on tubers is incredibly delicate and can easily be broken while digging. 
  • Lift the tuber from the ground and shake off all the soil. You can also use a hose to remove the clumps of soil or just swish it around in a bucket of water. Soil has several microorganisms that can cause the tuber to decay or rot in storage, so it’s better to get rid of as much soil as possible.
  • Remove or cut off all rotten tubers. 

Storing Dahlia Tubers in Winter 

Here’s how you can store dahlia tubers during the cold weather: 

  1. After you’ve dug up the tubers, set them aside to dry and cure. It’s advisable to dry the tubers naturally by placing them upside down in the sun for a couple of days. You can also keep the plant in a well-ventilated room that has a constant temperature of 60-70˚F.
  2. Fill a cardboard box or plastic bag with loose, fluffy material, like styrofoam peanuts, wood shavings, or vermiculite. Once the tuber is completely dry, place them inside. Cover them with a bit more of the storage medium, and then store them in a cool spot. 
  3. Keep the box or bag in a frost-free, well-ventilated place. A temperature of 40-45˚F is perfect, but 35-50˚F is also acceptable.

You can leave the tuber clumps intact for storage and then divide them later in the spring, or you can just divide them in the fall. Some people find that it’s better to divide the tubers before storing them, as divisions are easier to store. 

It’s advisable to occasionally check the tubers over the winter. Make sure you also remove any rotten tubers before they spread the decay to healthy dahlia tubers. 

Readying for Summer 

Once spring arrives, separate healthy dahlia tubers from the main clump and remove any rotten or wrinkled ones. Make sure that each tuber has at least one bud or “eye,” or it won’t grow into a healthy, blooming plant. 

If winterizing seems like too much work or you don’t have enough storage space, just skip the entire process and start over by purchasing new dahlia tubers in the spring. 

Leave a Comment