Some of the best tips for growing dahlias from seed include ensuring that the plant has the correct environment to thrive in, such as an appropriately sized and correctly prepared seeding tray, good soil, and enough water and light. Preparing the seeding tray is generally the first step to take when growing dahlias from seed, and should be large enough to allow for each seed to have enough room to grow. Seeding soil, which is specifically formulated to encourage healthy sprouting, can be used for optimal results, although potting soil can also be used with little worry. Dahlia seeds usually need to be watered frequently enough to allow the soil to remain damp, and they must remain in a location with a temperature of 70 to 80 degrees Fahrenheit (about 21 to 27 degrees Celsius).
The tray used for growing dahlias from seed should be both deep enough and large enough for the number of seeds being planted. Seeds should be planted at least one inch (about 2.5 cm) apart, and approximately 0.25 inches (about 0.6 cm) deep. Seeding soil can be used for ideal results when growing dahlias from seed. This type of soil is generally very nutrient rich and light, allowing the seeds to have as little difficulty sprouting as possible.
When watering dahlia seeds, one should avoid overwatering, which allows the soil in the tray to become soggy or waterlogged. The soil should be checked every day and kept moist, which may be easier if a spray bottle is used to mist the tray when water is needed. Germination should occur within one to three weeks. Once the plants have an average of three sets of leaves, they are generally ready to transplant and be exposed to the outdoors.
The relatively simple transplantation process involves removing the young dahlias from the seeding tray and carefully placing them into individual pots or other containers. One of the best tips for this stage of growing dahlias from seed is to use a mixture of potting soil and sand in the transplant containers, at a ratio of about two to one of potting soil and sand. This helps to keep the soil light and eases the transition. The plants should not immediately be placed outdoors permanently but instead for only a few hours each day, incrementally increasing their time spent outside over the course of about a week. Once the dahlias have become used to their new environment and do not seem to be having any trouble, they can be left outside permanently.