Growing Dahlias Dahlias like to be grown well drained and slightly acidic soil with lots of organic matter. Dahlias can be very difficult to grow in clay.
If you have clay soil, you'd do best using raised beds to help with drainage.
If your soil holds standing water for more than 24 hours after a heavy rain, it has poor drainage and your dahlia will not tolerate planting there. You should always take a soil test and only apply fertilizerif it's needed for your plants. Never fertilize just for the sake of it. Over fertilizing can kill your dahlias.
Contact your local State Ag Extension agent for help with soil testing.
When looking at any fertilizers, The first numbers are Nitrogen (N) the second is Phosphorus (P) and third is Potassium (K). The numbers represent what percent content of each of these nutrients. For example, a fertilizer that reads 10 – 10 – 10 contains 10% N, 10% P, and 10% K by weight. Dahlias require nitrogen but too much can cause the plants being nice and full and green, but produce few blooms.
Dahlias can be grown in soil with a PH no higher than 7.5. Dahlias grow to a large size and they have a shallow root system, so you need stake them.
When only growing a few dahlias most people either tie them to a bamboo stick, or use tomato cages.
When planting in a row, you can also run strings on either side of the row supported by anchor posts at the end of the row to prevent breaking and tipping.
Pinching dahlias when growing them can produce a bushier plant with more stems. This is normally done by cutting the plant after the 3rd or 4th leaf set. Deer normally will not bother dahlias. Although here in Pennsylvania the deer are always willing to try something once.
Major pests are insects such as aphids, thrips, Japanese beetle, cucumber beetle, and earwigs. Additionally, there are several fungal issues you may experience on your dahlias. There are many methods of controlling these pests. Bug traps, removing by hand, or biological alternatives. Whenever using a pesticide, organic or conventional, you must follow label instructions. Not doing so will cause environmental harm and is a Federal offense.
The most common fungal issue you may experience is Powdery Mildew. This can be reduced by not watering the leaves of plants. Powdery mildew normally doesn't show until the end of the season and we normally do not need to treat it as the flowers are almost done.