Hello dahlia lovers!
If you are new to dahlia planting this season, here are a few tips to get you headed in the right direction. I hope this guide is helpful. Please let me know in the comments if you have any questions. Happy growing.
1. Wait until all danger of frost is over and try not to plant just before a stretch of rainy days. Dahlias don't like to be too wet when they are settling in. If you really want to get started, you can pot up your tubers inside before you plant them out. A 3-quart (generally called 1-gallon) pot is a good size to start them in.
2. Choose a sunny, well-draining place in you garden. Or build up a raised bed to make a well-draining place. You can add a little compost, but generally dahlias do not like nitrogen-rich soil. So don't worry about fertilizing them. You may end up with more leaves and fewer flowers if you do!
3. Dig a shallow hole or trough in the soil and place your tuber in so that the end with the growing points "eyes" is up, or even just a little higher than the other end. Cover the tuber with some soil. Water it in a little if you have dry soil.
4. When your dahlias reach 8-12 inches tall, pinch off the center growing tips on the stem. It sounds awful, I know! But do it. You will be rewarded with a bushier plant with more stems and more flowers.
5. Cover your dahlias with a frost cloth or blanket if it looks like you might get a late frost. Dahlias do not like cold weather. If yours gets a little frost nip, you'll notice that the leaves turn brown-black and the plant starts to die off. Cut back all the dead/dying material and be patient. I've had plants regenerate from light spring frosts. Dahlias bloom in late summer and early fall.
6. Once started, dahlias do like to have a good drink, especially when the days get hot. Be sure to set up a drip hose on a timer or remind yourself to water your babies regularly.
7. Protect your dahlias from common pests. As a recreational gardener, I didn't have any trouble with pests in my home gardens. Now that I'm growing on a larger scale, I do. Early in the season, Potato Leaf Hopper bugs damage plants by sucking from the bottom side of the leaves. A diluted organic Pyganic spray can help you get rid of them. Later, I have trouble with Tarnished Plant Bug. They damage the blossoms by eating just one or a couple of cells from the bud. As the flower develops, it will exhibit a half-face or a large wrinkle in the flower head. We use organza bags from uline.com to cover the new buds until they bloom. We have several different sizes from just a few inches wide to about 14 inches for the dinner plate dahlia blooms. The standard yellow, hanging Japanese beetle traps will help control those monsters.
8. As dahlias grow taller - some quite tall - they may need some kind of corral system. We use simple wooden or metal steaks and synthetic twine to keep heavy stems from bending and breaking.
9. When you are ready to harvest some stems for cut flower use, cut deeply into the plant and take a long stem. Remove side shoots and extra buds you don't want from your stem. This encourages the plant to make more long stems. It can be hard to cut flowers you've been mothering, but when you do, the plant actually grows more flowers than it would otherwise. If you leave the flower and it goes to seed, the plant thinks, "all right, I'm done! I made seeds. Mission accomplished." We try not to let that happen :)
10. Dahlias last longest if harvested when they aren't quite fully open. Some people say they should be cut before the back petals get weak and papery. Young buds will not develop and bloom after cutting. An industry tip for dahlia harvesting is to cut them and place the stems immediately into a few inches of hot water. Let the stems rest in the hot water "dip" until they cool in a few hours and then place them in cold water. Something about that hot water dip helps them hydrate better. Cerinthe (Honeywort) is the same way.
I hope I covered the most important details. If you have any questions, please let me know. I'll do my best to answer your questions, or I'll ask some friends who are really accomplished dahlia growers. Thanks for following along and enjoy your dahlias!