Dahlia Growth Stages


Understanding the growth stages of dahlias will help you be a better gardener. What is its life cycle?
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Dahlias are among the most visually appealing flowers that you can grow. They may seem a bit intimidating at first, but they are no more difficult to grow than any other flowers in your garden. Understanding the dahlia’s stages of development can assist you in identifying any problems that may arise.

Dahlias have a fairly predictable life cycle that consists of seed, germination, vegetative growth, flowering, pollination, and seed dispersal.

In this article, I’ll go over the various stages of its development. 

Pink dahlia flower in full bloom

Understanding the Life Cycle

If planted as tubers, dahlias take about eight weeks to bloom. Planting seedlings in April, for example, should bloom by June. However, most dahlias bloom in response to warm weather in July and last until September or October. 

The first step in planting dahlia seeds is harvesting mature pods or purchasing seeds from a reputable dealer. To harvest seeds, wait until the ray petals have fallen off the flower and the pod has turned a pale tannish green. The seeds should be mature and gray to dark brown on the inside.

Seed Stage

Every seed contains an embryo, the earliest forms of a plant’s roots, stem, and leaves. A dahlia seed is easily identified because it resembles small black pellets with one end slightly skinnier than the other. 

Seeds should be started indoors 6 to 8 weeks before the last frost date. It takes approximately 100 to 120 days to produce flowers.

Germination

Dahlia seedlings must be potted if they cannot be planted right away. Sow the seeds 14 inches deep in the soil. You must wait until the risk of frost has passed before planting them because they are not cold-hardy. A soil temperature of at least 60ºF is required.

Dahlias can germinate in 3 days to 3 weeks, depending on the variety, seed quality, and growth conditions. Unlike vegetable seed, dahlia seed does not sprout immediately; germination can take several days. It is not good to overwater or keep the soil soaking wet.

Dahlias are a type of dicot. Its sprout is bright green and has two spherical, oblong leaves. A tiny line runs down the center of each leaf. The cotyledons are the first leaves to appear. 

Dahlia seeds grow into slender tubers that appear in the first year. The plants will need another year or two to establish healthy growth nodes and yield bold, colorful plants.

Dahlia seedlings planted in a home garden

Vegetative Growth

The tiny seedlings are ready to be separated and transplanted into small plugs or pots when they reach about 3 inches. Fill these pots with the same potting soil used to germinate your seedlings. After repotting, water the seedlings enough to keep the soil moist. They should be kept in pots for 4 to 5 weeks before transplanting outside.

Before transplanting young seedlings outside, they must slowly adapt to the outdoors. Gradually shift your dahlias outside to acclimate them to their new environment. Each day, increase the time until your seedlings have spent a few nights outdoors. Too much wind or rain will harm your delicate plants, so start the acclimation process on a day with a mild weather forecast.

They should be placed in a cold frame or left out during the day and brought in at night for 7 to 10 days to help condition the immature seedlings and reduce shock when transplanted. 

Flowering

The flower is the sexual reproductive organ of the plant. Flower petals are often prominent (depending on the seed type), vividly colored, and intensely fragrant to attract pollinators. Flowering is an exciting stage in the plant’s life cycle! The center of a dahlia flower is usually the most fertile region.

whte and pink edinburgh dahlia flower

Pollination

All dahlias have both male and female reproductive organs.

The pistil, the feminine component of the flower, comprises the stigma, style, and ovary. The stigma represents the pistil’s head, the style represents the stalk, and the ovary represents the pistil’s base. The stigma collects pollen and transports it down the style (pollen tube) to the ovary, where it is fertilized. The seed will develop near the base of the ovary after pollination.

The stamen is the male component of the flower. The filament is the stalk, and the anther is the stamen’s apex. The anther is in charge of pollen production. Pollinators should deliver pollen to the pistil or female part of the flower.

The stigma (top of the pistil) will open in a Y shape as it grows, allowing pollen to be caught by the hairs. When pollen adheres to the stigma, it has the potential to travel down the tube and fertilize the ovary at the bottom; this usually takes a few days.

Another method of pollination is the use of different pollinators. Dahlias have beautiful blooms that attract bumble bees, honey bees, solitary bees, butterflies, and other pollinators.

A bee pollinating in a yellow Dahlia flower

Seed Dispersal

Seed spreading, also known as seed dispersion, is the final stage of the flower’s life cycle. Seeds can be distributed in various ways, but Dahlias rely heavily on humans.

Dahlia seed pods contain a large number of seeds. You must wait until the blooms have shed all their ray petals and the pod has turned a light tan-green color; the seeds inside will be gray to dark brown, indicating maturity.

A dried dahlia flower under the heat of the sun
Alaine Connolly
Alaine has been working way too hard in horticulture since 1992, beautifying golf courses, resorts, and hotels. She is a part time landscape designer who works full time caring for a 28,000 square foot public garden. At home, she maintains her own 400 square feet plot. Alaine lives in northern Illinois - zone 5b.
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