Planting Dahlias – a Complete Guide

Dahlias come in the shape of colourful, spiky blossoms, which traditionally bloom from midsummer to the first frost.

This is one of the reasons for their popularity, as many flowers are unable to thrive for this length of time.

Planting Dahlias – The facts

Dahlias come in a rainbow of hues and sizes, from two-inch lollipop-style pompons to the impressive “dinner plate” blooms, which measure a massive 10-inches in size. The majority of varieties grow between four and five feet tall.

Although they thrive in most climates, they’re not well suited to extremely hot and humid conditions.

These species of plants are able to add colour and vibrancy to any sunny garden and boast a remarkable growing season of 120 days.

Planting Dahlias

It’s important not to be in a hurry when planting dahlias, as they will struggle in cold soil. Choose a time when ground temperatures are around 15°C and avoid planting in spring frost. If you plant tomatoes, plant your Dahlias just after these have been established.

Choose an environment with full sunlight. When planting dahlias, it’s key to know they thrive in six to eight hours of direct sunlight per day. For best results choose a spot sheltered from harsh winds too.

These species of plants prefer well-drained, rich soil. The pH level of your soil should be around 6.5-7.0 and be slightly acidic. Simply add peat, sand, moss, or bagged steer manure to heavier soil to lighten and loosen the texture. This will also encourage better drainage.

If using bedding dahlias, these can be planted nine to 12 inches apart. Smaller flowering types, which usually measure three feet tall, should be spaced in two feet intervals. The larger, taller blooms should be spaced three feet apart.

It’s a good idea to make the planting hole slightly larger than the root ball and to add some sphagnum peat moss or compost to the soil. For best results, add a handful of bone meal to the planting hole.

What to avoid

When planting dahlias, avoid tubers that look rotten or wrinkled. Green growth is a good sign! Don’t break or cut individual dahlia tubers, and instead, plant them whole. For best results, plant the crowns just above soil level.

If planting large, tall blooms, it’s likely they’ll require support. In order to ensure they don’t fall, use stakes measuring five to six feet tall. Place these around the plants and tie to the stems as the plants begin to grow.

Cut flowers

Larger dahlias are often grown solely for use as cut flowers and are best grown alone in devoted plots, as this will ensure there is no competition from other plants.

Dahlias of medium to low height, however, perfectly complement a range of other summer flowers. When planting dahlias, you’ll have to wait around eight weeks for the first bloom. If planted in the correct season, this is usually mid-July.

Dahlia Care

Avoid watering tubers post-planting, as this can promote root rot. In fact, there’s no need to water the plants until the dahlia shoots appear. Once the dahlias are established, you can then begin to water them two to three times a week with a sprinkler. This should be tailored to the climate.

Dahlias enjoy a low-nitrogen liquid fertilizer (similar to the fertilizers used for vegetable plots). The likes of a 5-10-10 or 10-20-20 will work well. Fertilize post sprouting and then every three to four weeks thereafter, from mid-summer right up until early autumn.

Pests and Diseases

Like many plants, Dahlias are affected by a number of unwanted pests. Thankfully all can be treated as follows:

Slugs and snails: Bait two weeks post-planting and continue throughout the season.

Mites: Spray plants at the beginning of July to late July to avoid spider mites. Sprays vary per area, which means it’s best to speak to your local garden center in order to ensure you invest in the correct one.

Powdery Mildew: This commonly shows in autumn. As with mites, you can prevent this by investing in a suitable spray.

Earwigs and Cucumber Beetle: Although they eat the petals, they don’t tend to hurt the plant itself.

Storage and Harvest

If growing dahlias in colder climates, it’s best to dig up the plants during the winter months and store them in a frost-free environment, until the warmer weather arrives.

To do this, cut foliage back two to four inches above the ground and gently remove the tubers, shaking away any excess soil.

Place in loose, fluffy material and store in a well-ventilated place. When spring arrives, separate them from the parent clump, and replant.


Lily Calyx is our in-house flower whisperer, an expert on all things botanical and an enthusiastic orchids collector. She loves discussing the insights of the secret world of flowers, shares her gardening tips and hacks and moons over the latest additions to Serenata Flowers flower range. Ask Lily anything about flowers and we can guarantee she will have the answer.

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