Ready to Get Growing?
Once the plant is sprouted and growing, dahlias need regular, consistent watering. We like to use drip tape, or a soaker hose if you're a home gardener) to be sure that they receive sufficient water. When we were growing in the very dry and hot climate of the BC interior, we would usually water 2-3 times per week in the peak of the summer. But in wetter climates this may be different. Check the soil moisture not just at surface, but at 6 inches down to see if your irrigation (or rainfall) is penetrating and providing sufficient moisture.
Keeping your plants well fertilized is an important task throughout the season. As we said earlier, healthy soil grows healthy plants! Often people want a specific fertilizer recipe and regime to follow, but every garden and climate is different and you'll need to tailor your program to your particular space. (Keep in mind that over fertilizing isn't good either! It can be detrimental to our environment as well as your plants.) We often use a product called Neptune's Harvest that is a mixture of fish and seaweed. We foliar feed our plants regularly- at least every-other week- throughout the growing season. For home gardeners it's as simple as adding a few TBS to a watering can! One important thing to know is that once your plants are established, you don't want to give them high nitrogen fertilizer. When you see 3 numbers on a fertilizer product label the first number represents the percentage of Nitrogen. This can cause plants to rapidly put on lots of green lanky growth and result in small blooms or low flower production. According to Swan Island Dahlias, it can also be a cause of tubers shriveling in storage.
To control weeds, you can mulch your plants. Quality straw, that is free of weed or grain seeds, is a good choice as well as decomposed leaf mulch. It is advised to wait to apply mulch until your plants have emerged and the weather has warmed up so that you don't unintentionally cool the soil and slow growth. You can also top-dress your plants with a thick layer of well aged, quality compost to help prevent weeds.
To encourage branching and a bushier plant, pinch your dahlias when they are approximately 8-12 inches tall. Simply snip (or pinch!) the central growing stem just above a set of leaves, leaving about 3 sets of leaves on the plant. Although it sometimes feels like it's the wrong thing to do (why am I chopping of 4 good inches of my plant?!), you'll be glad you did! It encourages the plant to branch out and essentially make more flowers with better, longer stems for cutting. Even if you don't plan to cut your flowers for the vase, it still encourages the plant to put out more blooms.
Dahlias will also benefit from staking. There is nothing worse than watching your beautiful plant that was just about to flower topple over in a rain or wind storm! Home gardeners can just use a wood or bamboo stake pounded in the ground next to the plants and then tie the main stalk to the stake as they grow. We pound in metal t-posts at the ends of our beds, and then along each side spaced about every 7 ft or so. We then tie and run sturdy twine down the sides, wrapping in around each post to create a corralling effect.