Growing Dahlias Guide

Growing dahlias:

Plant your dahlias when soil temperatures are at least 60 degrees, usually in May – Mother’s Day is a great target date for my farm in Western Washington. But with weird weather abounding, I take my cues from what the garden is doing. For example, if I see volunteer sunflower seeds popping up, I know it’s warm enough to get my dahlias in the ground.

I suggest planting them horizontally, because I don’t want to dig such a deep hole and as long as the eye of the tuber is 3-4 inches below the surface, all is good. I put a handful of organic fertilizer in the hole as well, which my dog loves to dig up and roll in. Grrrr. 

Everyone says to plant dahlias 12” apart. I plant them much closer and all is fine. You do you. I plant them about six” apart in staggered rows. 

Dahlias need support as they grow, otherwise wind and rain will knock them over and that is such a sad day. You can use a stake, but if you do, please be sure to put the stake in first before you plant so you don’t accidently skewer your tuber. You can also use a tomato cage. Or you can use this netting from Johnny’s Seeds (Hortonova netting) if like me, you cannot control yourself and have rows and rows of blooms. I hold the netting with metal t-posts in four-foot wide rows. 

Don’t actively water your newly planted tubers until you start to see sprouts but also don’t worry if it rains, all will be well. 

Now for the emotionally tough part: you are going to need to pinch your dahlia plant when it gets to be between 8”-12” tall. You won’t like doing this, but it’s soooo necessary if you want so many more blooms. I did an experiment and found that I got at least four times more blooms. Crazy! Dahlia grow with sections to their stems, similar to bamboo. You are going to want to pinch the center stem back to be 4”-6”, leaving 2-3 clusters of main leaves. This will force the plant to branch out and each of those branches will have flowers. If you don’t pinch, your plant will grow a single main stem and get to blooming as it wants to reproduce quickly. But that one stem will produce a limited number of flowers on that single stem and you may be disappointed. By pinching, you are slowing down the flowering by about a week but will be rewarded with bushy, bloom-covered plants. Yay! 

I suggest fertilizing the plants several times over the growing season. At planting, a balanced organic fertilizer is great. During growth and blooming, a fertilizer with lower nitrogen is better to promote blooms instead of foliage. 

When harvesting, cut deeply into the plant to give yourself a nice long stem – at least 8”. Yes, that means you are sacrificing flowers but you are again encouraging branching, leading to additional flowers. This way, you get lovely big bouquets while giving your future self even more flowers. It’s a win!