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Growing Dahlia Indoors from Seed, and Cuttings

Introduction to growing Dahlia indoors

Dahlia is a genus of tuberous plants that are members of the family Asteraceae; related species include the sunflower, daisy, chrysanthemum, and zinnia. The plants grow from small tubers planted in the spring. Dahlias plants are relatively sturdy plants if grown in the right lighting, heat, and soil. Care of Dahlia flowers vary dependent upon your zone, but here are a few Dahlia growing tips to help you get maximum blooms and healthy, bushy plants. Dahlia plants produce bright, beautiful flowers that come in a wide range of colors. Due to their height and weight, many gardeners feel skeptical about planting them in pots. However, Dahlias can thrive in large containers; tall varieties need a stake for extra support. With the right growing conditions for Dahlia plants and a little care, you’ll enjoy gorgeous, showy blooms all summer long. In this article we also discuss below topics;

  • How long do Dahlia plants take to grow
  • Dahlia plant care
  • Growing Dahlia from seed
  • Do Dahlias do well in pots
  • How do you care for potted Dahlias
  • How long does Dahlia take to bloom from seed
  • Are Dahlias hard to grow
  • Growing Dahlia from cuttings
  • Tips for Growing Dahlia in pots
  • Different varieties of Dahlia plants
  • Growing Dahlia from tubers
  • Growing Dahlia problems

A step by step guide to growing Dahlia indoors

A guide to growing Dahlia indoors.
A guide to growing Dahlia indoors.

Suggested Dahlia varieties

Select a species of Dahlia that suits your space;

First, purchase Dahlia tubers online or at a local garden center. Dwarf and low-growing Dahlia varieties are best for container growing. Some varieties can grow as tall as 5 feet, so you’ll need a much larger pot if you choose a tall plant species.

Small to medium varieties contain Bednall Beauty, which grows up to 2 feet, and Bishop of Llandaff, which grows up to 3 feet. Larger varieties contain Hadrian’s Sunlight and Twyning’s After Eight, which grow 4 feet or higher. A single Dahlia tuber needs about 1 to 2 feet of space, so you’ll probably only need 1 per container.

When to plant Dahlia tubers

Your tubers can go directly into the ground in the spring when the ground has warmed and there is little chance of frost. If you want blooms as early as possible, you can start the Dahlia tubers indoors in good light about a month before planting time. You will then have a small plant ready at planting time and Dahlias can be planted as late as mid-June in most parts of the country.

Where to plant Dahlias

Dahlias need a site with good drainage and partial to full sun. Pots are increasingly popular ways to grow Dahlias.

Soil temperature influences Dahlia growth

If you plant Dahlias in the early spring, the cold soil hinders initial growth your soil needs to be warmer than 16°C for Dahlia tubers to sprout. Because of the initial slow growth, you want to avoid watering Dahlia tubers until sprouts are visible above the soil surface. To encourage faster sprouting and blossoming, use a soil thermometer to gauge the best temperature levels. If you live in a particularly wet climate, growing Dahlia plants in pots offer sharp drainage, which helps to keep the tubers from becoming waterlogged.

Starting Dahlias indoors/growing Dahlia indoors

For most home gardeners, we recommend giving plants a head start in containers while soil warms up outside reaching at least 15°C. If that’s not until late May or early June where you live, you can start Dahlias indoors, 4 to 6 weeks before your last frost date. In containers, lay tubers on their sides with the stems up and cover with about 2 inches of soil. Wait until you see new plant growth breaking through to the water. If you want to leave plants in the containers, choose more compact varieties before planting, and look for a 12 to 16-inch diameter container to plant the tubers.

How to plant Dahlias

Most Dahlias need to be staked and you want to plant a sturdy stake before you plant the Dahlia. If you put the stake into the ground after the plant is growing, take care to avoid damaging the tuber or the root system. Tomato cages can be a simple approach to staking.

Put the Dahlia tuber in a hole several inches deep with the “eye” on the tuber facing up. The eye is the point on the shoulder, crown, of the tuber from which the plant grows. If you are planting several Dahlias in the same location, they must be separated by about 2 feet to give each plant room to grow.

The procedure of growing Dahlia indoors

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The procedure of growing Dahlia indoors.
The procedure of growing Dahlia indoors.

First, choose a container that is at least 30cm in diameter and depth for optimum growth and plant one per container as they make large plants when fully grown. Use multi-purpose compost and add a slow-release fertilizer for strong plant growth. Plant Dahlia tubers as deep as you would when planting in the ground and insert stout support.

Step 1) Select 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 garden soil before planting will help.

Step 2) Plant after the threat of frost has passed and the soil should be warm and well-drained.

Step 3) Space tubers about 18 inches apart. Dig a hole about 4-6 inches deep and wide enough to accommodate the tuber. Place Dahlia tuber in the hole with the “eyes” at the top and back-fill the hole gently, covering the tuber completely with a few inches of soil.

Step 4) Do not water after planting, unless the soil is super dry and you want the soil to be just slightly damp. Too much water can cause the Dahlia tuber to rot. It’s wise to check the weather and avoid planting right before a huge rainstorm.

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

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

Step 7) Dahlia plants begin to bloom in late July and produce heavily until the first killing frost of the season.

Growing Dahlia from seed indoors

First, Dahlia seeds need to be sown between February and April undercover. Sow seed 0.5cm deep, in trays of moist compost. Place in a warm position 15-20°C and keep moist. Transplant seedlings, to trays or individual small pots when large enough to handle. Grow on in cooler, but frost-free conditions. Gradually harden off young plants before planting out after the risk of frost, May – June, spacing your Dahlia plants 30cm apart, in well-drained soil and a sunny spot.

Then, fill a pot or seed tray with moist compost and lightly firm the surface. Gently push your Dahlia seeds into the compost and don’t forget to label your seeds. Cover pots with an inflated clear polythene bag, and held in place with a rubber band. If sown in seed trays, cover with a propagator lid and Dahlia seeds should germinate with 5 to 20 days.

Sowing Dahlia seed – Dahlia seedlings will germinate within a couple of weeks. Once the ‘true’ plant leaves have grown, seedlings are ready to transplant into individual pots. Hold Dahlia plants by their leaves and gently tease them out of the soil.

Transplanting Dahlia seedlings – Gently transplant seedlings in 10cm pots of peat-free, multi-purpose compost, firm, and water well. Then, harden off plants by standing them outdoors during the day and bringing them in at night. Plant them in final positions once all risk of frost has passed.

Growing Dahlia from cuttings indoors

Dahlia plants are easily propagated from basal cuttings. In the spring once the tuber has started sprouting, choose strong, healthy shoots about 7.5cm long and remove them with a clean, sharp knife along with a small portion of the parent tuber. Remove the lower plant leaves and dip the base of the cutting in hormone rooting powder or liquid.

Make a hole for the cutting in a pot filled with suitable cutting compost using a dibber or clean, blunt stick and insert the base of the cutting with the first pair of plant leaves just above the level of the compost. Insert three cuttings per pot. Then, cover with a plastic bag held in place with a rubber band or in a heated propagator and place somewhere light, but out of direct sunlight. Label the pot and water it from above to settle the compost.

In about 3 to 4 weeks the cuttings will have formed roots, carefully pot each cutting individually into a 7.5cm pot and grow on, planting out after the risk of frosts. With regular feeding and watering, the Dahlia plants grown from cuttings should flower later the same summer.

Watering and fertilizing requirements for growing Dahlia indoors

Young Dahlia plants do not require a lot of water; in fact, excessive water can lead to rotting of the plant. For larger plants, a good rule of thumb is to water if the rainfall is less than 1 inch in seven days. Pots need more regular watering.

The best strategy for fertilizing is, to begin with, a soil test to determine the pH level and the specific soil needs. Lacking that information, the Dahlia plants will generally benefit from regular treatments with a water-soluble or granular fertilizer. Traditional wisdom for Dahlia plants is to treat with a high nitrogen fertilizer through the middle of the season but minimize nitrogen at the end of the season.

Protecting your Dahlia plants from pests

Small Dahlia flower plants are susceptible to slug damage. It is a good idea to manually remove slugs early each morning time or to protect them with a commercial slug killer. Japanese beetles seem to enjoy eating Dahlia blooms just they are ready for a bouquet. The best method of control is to manually remove the beetles into a bucket of soapy water.

Other insects can become a problem if you would like blooms to be “perfect”. If that is the case, you want to consider using an insecticidal soap or a commercial pesticide. Follow label directions carefully if you choose to do that. Protect bees, butterflies, and other pollinators in Dahlia plants by avoiding the use of chemical pesticides and herbicides. To discourage disease, keep Dahlia foliage as dry as possible and water deeply once or twice a week, allowing the top inch of soil dry out in between. Clip off the bottom 12 inches of foliage to encourage good air circulation.

Cutting Dahlias

Cut Dahlia stems when the central flowers are fully opened and cutting in the morning when the plants are full of water, will give you the longest-lasting cut flowers. Bring a bucket of water with you, when you cut, to plunge the plant stems into. Then, take a long section of the stem. The stems are sturdy and will make great arrangements.

When you get them indoors, plunge the stems into 2 to 3 inches of hot (not boiling) water, to seal them. Leave them there until the water cools.

Why won’t my Dahlias bloom?

Getting Dahlias to bloom can be as simple as getting their light and water requirements down. Dahlias bloom best in full sun, meaning at least 6 hours of direct sunlight every day. Even a little less than that means Dahlias produce only some flowers. Partial or more shade will probably mean Dahlias do not bloom at all. Water is another major cause of Dahlia plants not flowering. If they don’t get enough water, Dahlias do not bloom. If the soil around Dahlia is dry, moisten it to a depth of 1 inch. Keep it from drying out between watering by adding mulch and common mistakes that result in Dahlia not flowering is over-fertilizing. Sometimes fertilizer is too much of a good thing, and lots of nitrogen will make for plenty of lush, green stems but few or no flowers. Feed your Dahlia plants with fertilizer with little or no nitrogen and you’re not growing it for the leaves.

Commonly asked questions about growing Dahlias indoors

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Questions about growing Dahlias indoors.
Questions about growing Dahlias indoors.
Do you soak Dahlia tubers before planting?

Before planting, soak Dahlia tubers in a bucket of tepid water for an hour so they can fully rehydrate. Starting Dahlia tubers in pots will also encourage them to develop more quickly, so they’re likely to start flowering earlier.

How long do Dahlia seeds take to germinate?

Dahlia seed germination will usually be fairly rapid, 10-14 days, quicker if the temperature is higher. Most of the Dahlia seeds will germinate together so the compost can be removed from the pot and broken up for the seedlings to be removed.

Why Dahlia plant leaves curling up?

Yellowing and leaf curl can mean the presence of a virus and it can also occur from water stress (too much or too little), nutrient deficiency.

Why are my Dahlia buds not opening?

If your Dahlia produced some flowers but isn’t blooming anymore, or the buds don’t open, it might because you’re not deadheading it. If you remove the dead Dahlia flowers, the plant didn’t get its seeds and will try again by growing more flowers.

Why are my Dahlias losing color?

Other causes of faded flower color include the fact that flowers fade after pollination. Once pollinated, flowers no longer need to attract their pollinating suitors and, thus, begin to fade. Flowers may change colors or fade when they are stressed and this can happen if a plant has just been transplanted.

How do you save a dying Dahlia?

Remove and destroy the existing Dahlia plant, and solarize soil or fumigate it to decrease the soil-borne fungi population. Fumigate with a product that has a chloropicrin-methyl bromide combination. If you wish to re-plant Dahlias, plant them in a different location to avoid subsequent infection.

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