The Q&A Archives: Dahlias Growing Very Slowly

Question: I planted 5 dahlia tubers in the Spring, about May 20th or so. When I planted them, I also put a tomato cage in the ground as I had read that this lends good support (I am expecting 3-4 foot plants). So, now it is July 21st and the dahlia plants are only about 1 foot tall. Also, some of the leaves at the bottom of the plants are starting to yellow.

I have read many things about dahlias (maybe too many) and I followed the instruction in one write up that said to pinch the center shoot when the plants were 4-5 inches. Could
this have caused this stunting, or am I being too premature in my assumption that these plants will not grow to the 3-4 foot height that I expected? One of the plants is budding at
this short stage. What can I do?

Thanks , Birdine

Answer: It's true, there is such a thing as too much information. First hand experience is a great teacher for willing students, too! For instance, pinching back is recommended for SHORT varieties of dahlia, but large ones should be allowed to grow as tall as they want, and often cages or stakes, as you mentioned. You may have removed the majority of growing points from your plants, so they won't really thrive this year. If they lack leaves, they aren't storing nutrients in the tuber for better growth next year, and may simiply be drawing from stored food to grow this year. When you lift the tubers this fall, see if they have grown or shrunk. You may want to start with new tubers next spring.

You probably also read that they need a deep, rich, humusy soil, full sun and lots of air circulation for best growth. They prefer to be watered only when it's droughty, and only about once a week after bloom begins. I wonder about the fertility and/or pH of your soil. A pH that's out of their preferred range (6-7.5) will lock up essential nutrients and result in stunted growth. Bonemeal applied to the soil in June and early August encourages good root growth and enlargement of the tubers. What you can do now is make sure these conditions are met, and prepare for next year's planting. Hope this helps!

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