The second of two comprehensive blog posts on growing dahlias in your home garden. This blog post will cover all you need to know to plant out and grow incredible dahlias.

One of the most beautiful and coveted garden blooms, dahlias require a good bit of work but are also exceptionally rewarding. Their blooms are used in cut flower arrangements, in wedding and event work and are prized for their size and unctuous and luscious blooms.

Have you read Part 1 of this 2-part series?

Whether you’ve been pre-sprouting your dahlias or you’re just eager to plant the tubers you’ve saved or purchased out it is now time to plant out your dahlias. Before planting your dahlias out, you’ll want to be sure ALL chance of frost has passed. This means not just a date that is passed your presumed last frost date but one that is truly after you have consulted the forecast and see that over temperatures are steady around 10C/50F. Tubers and any greenery that are subjected to frost will not recover.

Planting

It is critical that you choose a very sunny and well drained spot to plant your dahlia tubers. You will get the most blooms and the largest plants from areas that have at least 6 hours of direct sunlight, and it is preferred to find a spot that has 8 hours of direct sunlight. Because tubers are sensitive to too much moisture, it is also critical that you select a place in your garden where water doesn’t pool and that you have good drainage. Tubers that are over watered or sitting in water logged soil will rot.

Before planting out dahlias that you have started indoors, you must first harden them off. This is the process of acclimating your plants to the UV of the sun and to outdoor conditions. Start by placing your plants in the shade for a few hours, gradually increasing their exposure each day to morning sun and then afternoon and longer hours in the sun. This process should be done over 5-7 days to properly harden off your plants.

If you’re planting more than one tuber (and we do hope that you are!) the suggested spacing between plants is between 18-24”. Most dahlia varieties (excluding the border style blooms) will grow up to 4ft/1.2m tall and 3ft/0.9m in circumference.

The Process

Start by digging a hole approximately 4-6” deep. Then add a good handful of compost or organic amendments made for flowers such as Gaia Green’s Power Bloom.
If you are planting out a single tuber, lay it horizontally with the ‘eye’ or shoot pointing upwards. Carefully backfill the soil and unless the soil is incredibly dry do not water your tuber in.
If you are planting out a tuber clump, follow the directions above however nestle the tubers so that they ‘eye’ is point upwards, follow as above.
Pre-sprouted dahlia tubers should be left uncovered if the growing shoot is less than 6in/15cm, watered minimally and backfilled as it grows taller.
Pre-sprouted tubers with growing sprouts that are over 18”/45cm should be pinched back to above the 3 rd set of leaves. Pinching is the act of cutting back the main stem above a set of leaves to encourage the plant to bush out and develop more stems from where blooms will form. These tubers should be planted and back filled with soil, and watered in.

Staking

At the time of planting your tuber(s), it is critical to also place a growing stake, which you will use to help train the plant to grow upwards. Stakes can be metal or wood, should be at least 4ft./1.2m tall and be placed next to the tuber at the time of planting. By placing your stakes at the time of planting rather than after, you remove the risk of damaging tubers by piercing them with a stake that is placed at a later time.

Growing dahlias in pots and containers

If you don’t have access to raised beds or an inground garden, it is definitely possible to grow dahlias in pots and containers. Because dahlias grow quite tall, a deep container is preferable and one that is at least 12in./30cm in diameter and in height. Good drainage in your container is essential and we encourage you to drill additional drainage holes into the bottom of your vessel if you feel that there is inadequate drainage.

Choosing a growing medium formatted for container growing is essential. Container mixes will have additions such as perlite to keep moisture in the soil.

Watering

Your dahlia plants require regular watering in order to thrive. A deep watering is preferred and you should water your plants based on ambient outdoor temperature and the quality of your soil. Sandy soil will have less water retention and require more frequent watering than clay-based soil. Dahlias in containers will have different watering needs as these containers will dry out very quickly and need more frequent deep watering, especially in the heat of the high summer.

Feeding

To get the most prolific and abundant blooms, it is essential to feed your dahlia plants with a fertilizer that is low in nitrogen. Too much nitrogen will encourage an abundance of leafy green growth and inhibit blooms from forming. Though not affiliated with this product in any way, Gaia Green Power Bloom (2-8-4) is a well-balanced amendment for your dahlia plants. Adding an organic fertilizer every 3-4 weeks is encouraged.

We hope you try your hand at growing dahlias this season and encourage you to follow along as we present the third installment of this growing blog on dahlias in the near future, where we will cover pests and harvesting your dahlia blooms for longest vase life.

Dahlia Growing Guide - Part 2