Common Issues with Zinnias And What to Do About It
Zinnias are one of our favorite flowers, because of their incredible color, easy growing habits, prolific blooms, and ability to attract pollinators. But even these stunning flowers can face a few challenges. Whether you're a seasoned gardener or just planted your first seeds, it helps to know what could go wrong and how to fix any issues that might crop up.
We get flower farming questions all the time, specifically about zinnias, so we thought we’d share some of the most common issues with zinnias and what you can do to keep your plants happy and blooming all season long!
Powdery Mildew
Powdery mildew looks like a white, powdery coating on leaves of the plant that usually starts on the lower foliage and spreads upward. It can be caused by humid conditions, poor air circulation, or overhead watering, all of which create a perfect environment for this disease.
What to Do:
Space plants out properly to improve air circulation.
Water at the base of the plant rather than from above.
Remove and dispose of infected leaves (don’t compost them).
Use a fungicide labeled for powdery mildew if the problem is widespread. Organic options like neem oil or a baking soda spray can be effective.
Our best tip to fight - foliar feeding the leaves with compost tea. Check out Adam’s video on how to create compost tea here.
Too Much Water (Root Rot)
When your zinnias have too much water, otherwise known as root rot, you may notice yellowing leaves, wilting despite moist soil, stunted growth, and sometimes, a foul smell from the roots. Zinnias dislike wet feet, so overwatering or poor drainage can lead to root rot and fungal infections.
What to Do:
First off, make sure your soil drains well. You can fix this with compost or sand if needed, or by making raised bed gardens for growing.
Let the soil dry slightly between waterings.
Water early in the day so the soil can dry out before nightfall.
If root rot is suspected, gently remove the plant, trim off mushy roots, and replant in fresh, dry soil.
Japanese Beetles
Japanese beetles are notorious zinnia lovers and will feast on both leaves and flowers. If your zinnias have skeletonized leaves (they eat the leaf tissue between the veins), holes in petals, or entire flowers have been consumed, it’s most likely Japanese beetles
What to Do:
Handpick beetles in the morning when they’re sluggish and drop them into soapy water.
Use row covers early in the season to keep beetles off young plants.
Avoid beetle traps nearby as they seem to attract more than they catch.
Apply neem oil or an insecticidal soap if infestations get out of control.
Leaf Spot Diseases
Leaf spot diseases look like brown or black spots on leaves, sometimes with yellow halos. Severe infections may cause leaves to drop. These diseases are caused by bacterial or fungal pathogens, often triggered by splashing water or humid conditions.
What to Do:
Avoid overhead watering and splash back from soil.
Prune away affected leaves and discard (not in compost).
Consider using a copper-based fungicide or a bio-fungicide if it persists.
Practice crop rotation and clean up all plant debris at season’s end.
Stunted Growth or Weak Stems
Zinnias with weak stems or who have been stunted will stay small, have thin stems, or flop over. Causes can include poor sunlight, overcrowding, or low soil fertility.
What to Do:
Make sure zinnias get full sun (6+ hours/day).
Thin seedlings to allow room to grow and encourage strong stems.
Feed with a balanced, slow-release fertilizer or compost to boost growth.
Pinch back early growth to encourage bushiness and sturdier stems.
No Blooms or Few Flowers
Sometimes, zinnias grow healthy green plants but with few or no flowers. If this is the case, there might be too much nitrogen in the soil, not enough sun, or overwatering has occurred.
What to Do:
Avoid high-nitrogen fertilizers (they promote foliage over flowers).
Ensure full sun exposure.
Deadhead spent blooms to encourage more flowering.
EXTRA TIP-Blooms Won’t Hold Up in a Vase:
Zinnia blooms have to be mature before they can be cut and used as a cut flower in a vase. The trick? Try the “wiggle test.” Gently hold the stem about 8–12 inches below the bloom and give it a little shake. If the flower head wobbles loosely, the stem is still too young and won’t hold up in a vase. If the bloom stands firm and steady, it has matured enough to be harvested. This simple test helps ensure your zinnias last longer once they’re cut.
Even though there are several issues to look out for, we want you to know that zinnias are very durable, easy to grow, extremely hardy flowers. Knowing some of the issues that may arise is just a ‘good to know’ and they’ll thank you for a little care and attention, should you need to give them a little TLC. With the right growing conditions, you'll enjoy a summer full of stunning blooms and less headaches. If you’re ready to start growing your own zinnias, stay tuned for more of our zinnia seeds to release in our farm store soon! Happy growing!
XX Jenn and Adam
