How Tall Do Dahlias Get? A Complete Growing Guide

Its hard for me to believe how much dahlias have changed our lives in the last few years… You can read more about it here, but long story short, my husband came home from work one day and declared that he wanted to start growing dahlias. As our love for dahlias grew, we read everything we could get our hands on… and my husband even joined the West Michigan Dahlia Association so he could soak up knowledge from dahlia experts and enthusiasts. In the past few years, we have gained so much experience and currently, we grow about 1,800 dahlias on our small farm.

Below, I’ve compiled a list of some of the most common questions we receive about dahlias. Hopefully this helps you feel more clear and confident about growing dahlias yourself!

1. Choose a location with at least 6 hours of direct sun (the more sun, the better!) and well drained, fertile soil. Compost and all-purpose fertilizer worked into the soil before planting will help.

2. Plant AFTER the threat of frost has passed (about May 15, here in West Michigan). The soil should be warm and well drained.

3. Space tubers about 18” apart. Dig a hole about 4-6″ deep and wide enough to accommodate the tuber. Place tuber in the hole with the “eyes” at the top (or lay it on it’s side) and back-fill the hole gently, covering the tuber completely with a few inches of soil.

4. DO NOT WATER after planting, unless the soil is super dry. You want the soil to be just slightly damp. Too much water can cause the tuber to rot. REPEAT: DO NOT WATER. Its also wise to check the weather and avoid planting right before a huge rain storm.

5. Once the plants have sprouted, you may begin watering regularly. When plants reach about 8″, begin fertilizing with all purpose liquid fertilizer about twice a month.

6. Pinch the plants when they reach about 12-16″, to signal the plant to produce more branches (and more blooms).

7. Plants begin to bloom in late July and produce heavily until the first killing frost of the season.

What is a “tuber”? Is that like a “bulb”?

• Dahlia tubers are sometimes called a “bulb”, but they are technically a tuber, similar to a potato. Similar to a potato, the tuber sends up a shoot that becomes the plant, which produces leaves and flowers. Underground, the tubers multiply each year (again, like a potato).
• You only need one tuber with one “eye” to successfully grow a vigorous dahlia plant. Ever left a potato in the pantry too long and noticed “eyes” sprouting? Same thing with a dahlia tuber.
• Watch the short video below to get an overview of dahlia tubers.

Interested in growing dahlias? Watch to find out how they grow… and multiply like crazy!

Tubers come in all sorts of shapes and sizes! Some are long and skinny, some are short and stubby, some are huge (up to 10” long!) and some are tiny (the size of your pinky).Click HERE to read “All About Dahlia Tubers”. It’s a common misconception that “Bigger Tuber = Bigger Plant”. This is not true. The tuber is simply the food source for the plant until they have about 3-4 sets of leaves. After that, the root system growing from the tuber is responsible for the health of the plant. According to Michael Genovese of Summer Dreams Dahlia Farm, a tuber the size of an AA battery or larger is considered usable. All three of the tubers pictured below are acceptable, but the two tubers on the right are considered ideal sized.

So if tuber size doesn’t matter, what DOES matter?

Two things are necessary for a viable tuber:

1. The tuber MUST have 1 eye. The eye is where the sprout will grow (similar to a potato left too long in the pantry).

2. The neck MUST be intact. If the neck is broken/snapped, the tuber is worthless.

Do I need to stake dahlias?

• Yes, most varieties will need to be staked, otherwise the wind may flatten and ruin the whole plant. Gently tie the plant to a sturdy wooden or metal stake. A tomato cage would also work!
• You can also use netting stretched between posts, hovering about 12-18″ from the ground. The plants grow right up into the netting, which keeps them in place.
• You can learn more about staking and supporting methods in this THIS BLOG POST.

5 dahlia growing tips in 5 minutes

FAQ

Do dahlias like full sun or shade?

Dahlias love to be in a sunny location— an area that receives at least 6-8 hours of direct sunlight is preferred. Dahlias will also grow in shady areas but generally will be taller and require more staking and care. Dahlias love to be in the dirt. The dirt is a friend to Dahlia Tubers.

Do dahlias come back every year?

The tubers that grow beneath the ground are unharmed and can live to perform again year after year given a little care from you. Some lift dahlia tubers and store them over winter, then replant the following spring. Others in milder areas leave them in the ground.

Do dahlias multiply on their own?

Dahlia plants produce tubers that grow in the ground. Each year the mother tuber (the original bulb) typically produces anywhere from 5-20 new tubers. By dividing these tubers in the winter, you can multiply the original plant and grow identical dahlia flowers.

Where is the best place to plant dahlias?

Dahlias need a sheltered spot, with as much sun as possible – a south or west facing border is ideal. Dahlias are not fussy when it comes to soil. For best results grow in any fertile, moist but well-drained soil. Enrich the soil with some organic matter, such as well rotted manure.

How big do dahlias grow?

Here are the three main size types and what they mean for you as a gardener. They grow between 3 and 4 feet tall. The best-known dahlias in this size range are dinnerplate dahlias, which have double flowers that are 10 to 12 inches across. The best place to grow these is in the back of perennial beds with other big perennials.

What size Dahlia should I plant?

Tall dahlias over 4 feet have the longest stems for cutting. Plant en masse for an abundant harvest. Compact border or dwarf dahlias under 2-3 feet are ideal for tiny yards, courtyards, and urban balconies. Giant dinnerplate and novelty dahlias make jaw-dropping focal points in large gardens.

Do dahlias grow too tall?

During the growing season, dahlias produce lush foliage and abundant blooms. As the season progresses, the plants get taller and taller. In order to keep your dahlias from growing too tall, you need to prune them regularly. The best time to prune is in the late spring before the plants start to become too tall.

How big do dinnerplate dahlias get?

Dinnerplate dahlias can reach heights of 4 to 5 feet and have blooms as wide as 10 inches. Because of their size, these plants require a sizable plot of land to flourish. You can grow dinnerplate dahlias in the back of a flower bed, against a fence or shed, or even in the vegetable garden.

How tall do border dahlias get?

Smaller in stature, border dahlias are ideal for containers. They are only around 15 to 20 inches tall, so they look great in front of a flower garden, along a walkway, or in a container. Remember that height isn’t everything. These short-statured dahlias are just as full of life and vitality as their taller relatives.

How do you grow tall dahlias?

Another method to encourage taller growth is to stake your dahlias. Use sturdy, metal or wooden stakes and place them in the ground next to the plants when they are still small. As the dahlias grow, gently tie the stems to the stakes using soft twine or plant ties.