The Midsummer Malaise
Have you looked at your dahlia plants this summer and thought: What is going on with my dahlia? It looks awful!
You may be suffering from what I call “The Midsummer Malaise” (TMM). TMM isn’t an official disease or anything like that. But it’s a common issue I see on Dahlias at least once a summer, especially if you live in a hot climate.
Usually it looks a little something like this. Brown crunchy or soggy (if it’s been wet) leaves or perhaps yellow leaves if you catch it early. These are signs of stress. Ideally dahlias love more moderate cooler temps- 60-70’s. Well most places don’t get those until Fall. But in order to have dahlias in the fall, you have to grow them through the summer. So you have to get them through the heat.
So what do you do about it?
1. Clean up the plant. Remove any brown, yellow, crunchy dead leaves— anything that’s not green and luscious.
They should look like the picture below. Some growers actually pre-emptively remove all the foliage on the lower 18” of the plant. But I find that’s a lot of extra labor for 2200 plants. So I remove it where needed.
2. Inspect the plants for any sign of disease- especially powdery mildew. PM looks like a white dusting on your leaves- when it starts, it can occur just in small spots on the leaves. We’ll talk more about how to deal with PM another time. For now just notice if the plants don’t look “normal.” And by normal I mean, they should be solid green - dahlias don’t have any variegation in the leaves. It’s very slight in the photos below but those lighter greenish yellow patches are a tell-tale sign.
If you see sings of yellow mottling, then you are going to want to investigate further. That could be a sign of disease or nutrient deficiency. I tend to treat for nutrient deficiency before assuming disease unless I see any other tell-tale signs of disease.
3. It’s time for a little TLC. Dahlias are pretty hungry and need to be fed regularly to perform well. So it’s time to fertilize.
The type of fertilizer is going to depend on the stage of growth. If your plant is less than about 6 weeks old then a fertilizer that includes a bit of nitrogen is good. Dahlias don’t need loads of nitrogen. Nitrogen promotes green growth. Generally you are looking for a fertilizer that is higher in phosphorus and potassium. This is a good time to know what nutrients your soil contains (hence the reason you always hear gardeners talk about taking a soil test).
***But I know most of us didn’t stop and soil test this spring. (Don’t feel bad, I didn’t test for several years when I started gardening). You can test this fall and you’ll be ready for next year!***
So if you don’t know what nutrients your soil is low in, you do fly a little blind. But since we know that dahlias like phosphorus and potassium, we’ll look for that. Fertilizers that are made for tomatoes or roses are also good for Dahlias. I encourage you to seek out an organic fertilizer. Also I prefer liquid feeds at this point. I use a powdered/granular fertilizer when planting but prefer liquid during the growing process. I just find it easier to apply. (Brands differ from place to place and that’s why I feel it’s more important to tell you what to look for in the fertilizer than an actual name brand.)
Feed your dahlias (according to the instructions on your fertilizer) about every other week from now until about a month before your first frost date.
4. Lastly, make sure your dahlias are getting plenty of water. You can’t do anything about high heat but you can control the moisture. I try not to let my soil completely dry out. You do want to make sure you have good drainage though. Dahlia tubers don’t like sitting in mucky wet soil.
The Midsummer Malaise is bound to get you at some point and some years it is more extreme than others. But it doesn’t have to spell a death sentence for your plants. It just means it’s time for a little garden therapy for you and TLC for your plants!