If the leaves on your zinnias are turning brown it’s time to figure out what’s going on. Thankfully it’s usually something straightforward.
Having grown zinnias for years I’ve seen their leaves turn brown many times. It’s not uncommon, so don’t be too upset you’ve done something really wrong.
With this guide I’m sure I can help you pinpoint what’s going wrong and how to fix it. So I’ll take you through some of the most common reasons your zinnias might be browning and how to solve it and keep them looking their best.
1. Watering
Water is, obviously, extremely important for your zinnias. But if you give them too much or not enough it can cause real problems.
Overwatering can lead to root rot which will makes the edges of the leaves turn brown. This is due to the extra water filling the air pockets in the soil and so the roots can’t get the oxygen the plant needs.
But underwatering will also cause problems. The leaves will become brown and crispy as it doesn’t have enough water.
- Check the soil regularly. If you feel it’s soggy then stop watering as regularly. If when you put your finger in the soil it’s dry at about 1 to 2 inches down then you should be watering.
- Make sure you’re watering deeply but not as often. This will help the roots to grow but also stops you from either over or underwatering. As a rough guide aim for around 6 to 8 inches of soil to be wet.
2. Fungal Diseases
Zinnias can get fungal diseases, especially if they’re growing in high levels of humidity. The likes of powdery mildew will cause a white or grey powder on the leaves. Alternaria, enough fungus, cause dark brown spots on the leaves that will kill them given enough time and no treatment.
- Remove the leaves that have been affected as quickly as you can to stop the spread.
- Use a fungicide like neem oil to treat the remaining plants.
- Make sure your plants have enough space between them that the air can circulate fully and keep the humidity low.
3. Sunburn: Too Much Direct Sunlight
Zinnias love the sun but if they get too much their leaves can become burnt and brown on the edges and tips. This usually happens where the summer sun is more intense and will cause them real stress.
- If you’re growing your zinnias somewhere that gets very high temperatures in the summer then give them some shade in the afternoon either with a cloth or plant some taller plants.
- Your zinnias should be getting around 6 hours of direct sunlight every day. Be careful to look out for signs of burn though.
4. Nutrient Imbalances
A lack of imbalance of nutrients is another problem that can cause browning leaves. Not enough nitrogen, for example, will show up as yellowing. But a lack of potassium or phosphorous can result in brown edges.
But at the same time if you over fertilize zinnias then salt can build up in the soil which also causes brown leaves.
- Test your soil first so you can see if there’s an imbalance of it’s lacking in any nutrients.
- Use a balanced fertilizer that has nitrogen, phosphorus and potassium in it. But don’t go mad. Fertilize once a month during the growing season.
- If your soil is too salty you might need to give it a really good watering to flush the excess salts out.
5. Pests
Aphids and spider mites can affect your zinnias. They suck the sap from the leaves and this will lead to brown and yellow leaves.
- Keep checking your zinnias for pests on a regular basis.
- Treat any pests you find with insecticidal soap or neem oil.
- If you spot ants that’s often a sign of aphids. So if you control the ants that can help to keep the aphids down or away.
6. Environmental Stress
While zinnias love the warmer weather they are very sensitive to frost. If the temperature drops very suddenly then that can cause the leaves to turn brown very quickly. Even overnight in some cases. On the same lines if your zinnias go a period without water they will get stressed and this will lead to wilting and browning leaves (and eventually death).
- If you know frost is coming, cover your plants with a protective fabric to keep them insulated.
- During droughts, water your zinnias deeply but less frequently. Mulch can help retain soil moisture during dry periods.
7. End of Life Cycle
As zinnias are annuals it means they live out their whole life cycle over the course of one season. So when they mature and set seed the leaves and flowers will naturally turn brown and die off.
- Deadhead any of the spent flowers as it will help with encouraging more flowers to grow in the growing season.
- Once your zinnias have matured fully and gone to seed you can collect the seeds and plant them the next season.
Tips for Growing Healthy Zinnias
Once you’ve fixed or avoided brown leaves you can focus on growing healthy zinnias:
- Plant in full sun: Zinnias do best in sunlight but watch out for stress from the heat, especially in very hot summers.
- Use well draining soil: Zinnias don’t like to sit in wet soil! So add compost or sand to your soil if it’s too heavy.
- Water wisely: Deep watering that you don’t do very often is better than shallow but frequent watering.
- Fertilize monthly: Use a balanced fertilizer but don’t overdo it. They like a little and too much will damage them.
Once you’ve dealt with these common causes of browning leaves and followed the few simple care tips you will be able to get beautiful and healthy zinnias throughout the growing season.
