3 Disease Resistant Perennials for Summer Color

By mid to late summer, many northern gardeners notice disease becoming an issue for some of their favorite perennial plants. Tall garden phlox (Phlox paniculata), bee balm (Monarda) and spike speedwell (Veronica) are three classic cottage garden perennials that many gardeners see disease on, but there is hope! Some varieties are far more disease resistant than others.

The first step is to understand what you’re dealing with. Powdery mildew is often the culprit when you’re noticing issues with these perennials. There are a number of different kinds of fungi that cause powdery mildew, but you’ll notice them all as white spots or coating mostly on the leaves. It can also turn the leaves yellow and cause them to drop. In damp weather, fungal spores land on the plant. Then when it’s warm, sunny and humid, the spores grow and start to cause issues.

The best way to avoid issues with powdery mildew is to grow disease resistant varieties of perennials that are traditionally susceptible. I’ll show you some of my favorites next, then tell you what I recommend as preventative sprays for varieties that aren’t as disease resistant

Disease Resistant Tall Garden Phlox

Tall garden phlox is a glorious native perennial for providing vibrant color from mid to late summer in northern gardens. It prefers full sun to part sun in zones 3-8. However, this type of phlox is also notorious for getting powdery mildew. You can reduce its susceptibility to the fungus by growing it in full sun with good spacing to encourage good airflow among the plants. Keep the soil moist, but well-drained, and mulch around the base of the plant with wood chips.

Three excellent varieties of powdery mildew-resistant phlox include:

Luminary^® 'Ultraviolet' – Features incredibly dark magenta, fragrant flowers on 32-36” tall plants.

Luminary^® ‘Sunset Coral’ – Features vivid coral pink flowers with a touch of orange on 30-32” tall plants. It’s a bee, butterfly and hummingbird magnet in the garden. 

Luminary^® ‘Opalescence’ – Produces large clusters of light pink flowers with a dark pink eye. This award-winning variety has exceptional resistance to powdery mildew.

Disease Resistant Bee Balm

Bee balm is another popular summer blooming native perennial that is a favorite of pollinating bees, butterflies and hummingbirds. It has a long history of use as a medicinal plant in Native American cultures but is also notorious for getting powdery mildew in the garden. To help avoid the issue, cut the plants back after they bloom and then apply one of the preventative sprays I’ll tell you about below.

I recommend growing more disease resistant varieties of bee balm like these:

‘Pardon My Cerise’ – A relatively short variety that grows 14-18” tall and blooms with bright cherry red flowers. Like all bee balm, it’s best in full sun and consistently moist, well-drained soil.

‘Leading Lady Plum’ is even shorter, topping out at 10-14”, but it flowers earlier than the Pardon My varieties. Its flowers are magenta purple and the fragrant foliage makes it deer resistant.



Upscale^® ‘Pink Chenille’ is more of a traditional bee balm that grows 20-22” tall. It becomes covered in large, almost fluorescent pink flowers in midsummer.

Disease Resistant Spike Speedwell

Spike speedwell is a classic sun-loving, clump-forming perennial for zones 4-8 that produces colorful flower spikes in shades of purple, blue, pink or white. Deer tend to pass it by, but butterflies and pollinating bees love it. Depending on which variety you grow, the flower spikes could be just over one foot tall or nearly hip high. Cutting the plant back after the first flowering may promote rebloom later in the summer.

While older varieties of spike speedwell are susceptible to powdery mildew, newer varieties like the three I’ll show you here have better resistance:

Magic Show^® ‘Pink Potion' is a relatively compact 14-16” tall variety that works well near the front to middle of the border. It’s packed with baby pink flower spikes in the summertime.

Magic Show^® ‘Wizard of Ahhs’ is even shorter, forming a low, wide clump of bright green foliage topped with vibrant violet-blue flower spikes. It needs a spot right in the front of the flower border.

Magic Show^® ‘White Wands’  is one of the longest blooming varieties of spike speedwell, producing tall spikes of pure white flowers beginning in early summer. Pollinating bees love this plant!

Preventative Sprays for Powdery Mildew

Once powdery mildew sets in, it is usually there to stay for the season. That’s why it is important to take steps to try and prevent it from happening. Growing disease resistant varieties like those I shared with you above helps a great deal. So does spacing plants further apart and thinning them out each year so the air flows better through them.

Spraying the plants with neem, copper or horticultural oils early to prevent powdery mildew from getting started and spreading is a good idea. They are less effective at curing the fungus once it sets in. I sometimes make my own spray by mixing one teaspoon of baking soda with one teaspoon of horticultural oil into one quart of water and applying it all over the plants.

If you’ve struggled with tall garden phlox, bee balm or spike speedwell in the past, I hope you are encouraged to try some newer, disease resistant varieties that should be easier and more reliable for you to grow. After all, sometimes the best remedy is to know the enemy so you can conquer it!