Dahlias for Pot Culture

General Information Dahlias originate from Central America. Flowering is regulated by the temperature, the number of hours of light per day, and light intensity. The information contained in this folder is intended to facilitate cultivating Dahlias as container plants in greenhouses. The purpose is to cultivate a flowering plant that can be traded as a finished product. Plants can be taken out of the pot and replanted in fertile soil in the garden, where they will flower and grow further until late autumn. The Dahlias can also be planted in containers 30 cm deep for the terrace or patio.

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If the plants are put straightaway in the garden or patio and on the terrace after buying, this can be done as soon as there is no longer any danger of (night) frost. From then on, the plants will flower constantly until winter. They are easy to look after.

Dahlias are, by nature, beautifully shaped and brightly coloured. As garden plants or plants in containers, they can be easily combined with other annuals or perennials. Dahlias are increasingly being used in this way. Garden centres and gardeners value this in particular. Selling potted dahlias adds to the sale of dry-selling tubers and even prolongs the selling period until after the summer holidays. It offers the consumer the possibility to fill up any empty space in the garden or on the terrace immediately with flowering plants.

If the tubers are not planted immediately after arrival, they should be stored at ± 50ºF.

General instructions

Always water them sufficiently
Remove wilting flowers
Add a fertilizer as soon as their growth slackens. A soluble type of fertilizer mixed in water gives excellent results. Use a well-balanced mixture, for instance, NPK 20-20-20. For quantity please read the instructions
Keep the plants free from parasites

Soil

For container growing we recommend a well-balanced and permeable mixture of earth, peat and garden turf. The mixture must be well drained, sterilized and should not contain bark.

PH: 6.5 - 7 EC:

Week 1 – 4: 0.6 - 0.8

Week 5 - 10: 1.0- 1.2

Value can be reached by apply of:

Organic fertilizer ±2 kg per m³ NPK 7-6-12+ 4Mg

0,5 kg PG-mix 12-14-24 + 2 - 2,5 kg Osmocote+ 15+10+12+2MgO+sp per m³

A fungicide drench is always a good preventative, especially for pythium.

Planting and Container Size

We recommend to use one tuber per 1-gallon pot. Plant tubers with the crown just below soil level. Particularly long roots or rootlets and possible old stalks that are too long should be shortened before a tuber is planted. After planting, the pots can be placed one against the other for the next 4 - 5 weeks. After weeks, give the plants some more space. Spacing allows more air movement and helps prevent fungal and stretching problems.

Pinching

Without pinching, the growth time is 8 - 10 weeks.

Pinching increases growth time by ± 2 weeks but results in a better-shaped plant with more stems and buds. The best way to create a well-shaped plant is to cut the developed shoots just above soil level ± 2 weeks after planting. The plant will immediately develop new and more shoots.

Light Conditions

In order to get the best performance from the plants, it is important to give them a lot of light. Lack of light may result in the plants becoming too long and limp. Grow dahlias with a maximum amount of available light with a minimum of 2000-foot candles.

A 14-hour day is required to keep dahlias vegetative, long days are needed for quality dahlia vegetative growth and timely bud development.

Temperature and Humidity

Week 1 - 4 Ideal growing temperatures range from 60 - 65 ºF during the day and 55 - 60ºF at night.

Week 5 - 10 Increase temperature to 68ºF during the day and 62ºF at night.

Temperatures above 80ºF can delay flowering. Warmer temperatures, then recommended, will promote a more open habit and weak stems. Shading at midday may be necessary.

Humidity levels range from 50% to a high of 80%.

Watering and Fertilization

Dahlias require that the planting medium stays moist but not wet
Week 1 - 5 EC can be maintained around 0.8; the next five weeks can be slightly higher
Osmocote 14-14-14 can be incorporated into the soil at a rate of 4 - 6 pounds per cubic yard
Constant liquid feed can be used at 200 - 250 ppm with 20-10-20 or 15-16-17
A combination feed using a multi-headed injector with 20-10-20, 15-0-15 and 20-35 magnesium
Potassium nitrate can be used to build stocky stems at 200 ppm

Pest and Disease Prevention

Thrip, mites, aphids, and whiteflies are potential pests. A preventative spray with adequate products is recommended
A fungicide spray in combination with an insecticide spray to prevent powdery mildew is recommended

Growth Regulators

The grower should evaluate growth at 2 - 4 weeks after planting. 1500 ppm of B-9 can be used as preventative sprays. Use of growth regulators after week 5 (generative crop) must be avoided. It has a negative influence on the development of lateral shoots and post-production of flowers.

Outdoor Growing

Apart from the greenhouse culture, it is also possible to choose a culture that is half indoors, half outdoors, or a complete culture outdoors. In the culture, half indoors, half outside, the first 4-5 weeks, the plants are grown in the greenhouse and by the time they need more space, they are moved outside. It's preferable to select an overcast day. Otherwise, protect the plants to avoid the risk of scorching. Cultivation can also be done entirely outside. In that case, planting can be started after the night frost has disappeared. Grow time outside may vary a bit depending on circumstances such as temperature and light. Outside care is identical to indoor care. See to it that the plants are always given sufficient water.

Keys to Success

Good potting soil
Good light levels
14 hours of day length
Good average of day-night temperatures
Moderate fertility levels
A preventative drench and spray program

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