Delphinium, with its stunning, towering flower spikes, is a total classic in any perennial garden. For the most part, these beauties are pretty low-maintenance. However, they do have one major nemesis: powdery mildew. This fungal disease loves to show up right when the weather gets hot and dry.
How to Spot Powdery Mildew
You’ll know you’re dealing with powdery mildew the second you see it. It looks exactly like someone dusted your plants with white flour. This coating can show up on both the tops and bottoms of the leaves, and because it thrives in sunny, dry conditions, gardeners often call it the “fair-weather fungus.” If left unchecked, it can spread to the stems and flowers, causing the plant tissue to turn brown and eventually die off.
Preventing and Getting Rid of the Fungus
While you can certainly grab a fungicide from the garden center to wipe it out, I’m a big believer that prevention is the best medicine. You can actually boost your Delphinium’s defenses by using a homemade herbal tea. Herbs like sage, yarrow, and especially horsetail are fantastic for this.
How to Make a DIY Horsetail Spray
- Grab a large handful of fresh horsetail.
- Let the plant soak in a bucket of rainwater for about 24 hours.
- Use a ratio of about 5 ounces (150g) of herbs per quart (1 liter) of water.
- Boil the mixture for about an hour to extract all those good minerals.
- Once it cools, dilute the “tea” at a 1:5 ratio with more water.
- Spray your perennials thoroughly, especially on hot days. It’s best to do this in the early morning or evening so the sun doesn’t scorch the wet leaves.
The cool thing about this horsetail brew is that it doesn’t just fight powdery mildew; it’s also great for other fungal issues like rust or even late blight on your tomatoes!
If you’d rather try a yarrow version, just boil about 2 ounces (50g) of yarrow flowers in a quart of rainwater and let it steep for three days before using.
