Tomatoes can develop brown leaf edges if they are getting too much water, if they develop sunburn, if they are overfertilized or underwatered. Once you identify and solve the problem the tomatoes can continue to grow new, green leaves on growth tips. Brown leaves can be removed by trimming them back close to the stem.
This article will explore the top reasons why outdoor tomato leaves develop brown edges and how to solve each one.
8 Reasons why tomato leaves get brown edges
Here are the top reasons why tomato leaves can get brown edges and how to solve each one.
1. Old leaves
The old leaves on tomatoes will eventually turn brown starting on the edges and spreading to the whole leaf. This will start near the base of the stem. This is a natural process and won’t harm the plant. These leaves can be pinched off or cut back with sharp secateurs.
Cut them close to the main stem but make sure you don’t damage it. This can allow an entry point for pests or diseases.
2. Insect attack
Insects can attack tomato leaves particularly new growth causing holes and brown and yellow edges. Aphids and spidermite are common pests that can suck the sap from the leaves. They can quickly multiple when the weather starts to warm up.
Spray the leaves with neem oil to get rid of these sap sucking insects. They won’t harm the beneficial insects or the plant. It can be applied 2-3 times until the pests are under control.
Chewing bugs such as caterpillars, snails and slugs can eat holes in tomato leaves causing them to turn brown on the edges.
3. Too much fertilizer
Tomatoes can develop brown leaf edges if they are given too much fertilizer. During the spring the plants will be growing rapidly but too nitrogen, potassium or phosphorus can cause fertilizer burn which can damage the leaves.
To avoid fertilizer burn and damaging the tomato leaves use a fertilizer specifically made for tomatoes or use an organic slow release fertilizer.
Build the soil up with compost and aged cow manure before planting. Add a handful of pelleted chicken manure 4 weeks after planting.
To encourage more flowers and fruit add a fruit promoting fertilizer towards the end of spring. This will increase the potassium to nitrogen ratio encouraging the plant to flower.
4. Frost damage
Tomato leaves can turn brown on the edges if they are damaged by frost. The cold will damage the cell walls causing them to burst and the leaf can die back entirely.
Young seedlings are more vulnerable to frost so aim to plant them after the last frost in spring. You can cover them with a plastic soda bottle overnight and in the morning to protect them when they are small.
Very hot weather and sun can cause tomato leaves to turn brown on the edges. If the tomato dries out too much it can cause the leaves to droop and eventually turn yellow and brown.
Sunburn will not harm the plant if it is watered well at the end of the day. These damaged leaves can be trimmed off to tidy up the plant or left on after frosts or the harsh sunny weather has passed.
6. Salty or chlorinated water
Tomatoes that are watered with ‘hard’ treated water can develop brown leaf edges. Some water sources can contain lots of salt, chlorine or other elements that can build up in the leaves over time.
Use rainwater if your town water is highly salted.
To remove the excess chlorine from the water, fill a bucket with your tap water and leave it outdoors for 24 hours. Lots of the chlorine will naturally break down and evaporate reducing the amount in the water.
7. Not enough sunlight
Tomatoes that are not getting enough sunlight can develop brown edges on their leaves. They will struggle to photosynthesize and can grow long, leggy stems.
Plant tomatoes in a position that gets lots of early sun. If you live in a hot and dry climate, make sure they have protection from the afternoon sun to avoid burn. Aim for at least 6-8 hours of sunlight throughout the day. This will give you more green leaves and delicious, sweet tomatoes.
Overwatering can cause tomato leaves to turn brown on the edges. Overwatering can wash away nitrogen from the soil causing the leaves to turn yellow and then brown.
Too much water can also cause the roots of the tomato to rot. Fungal growth can damage the root tips and stop it from absorbing the water and nutrients it needs.
Avoid overwatering tomatoes by using a dripper system. In summer they may need water everyday but it is best to do this early in the morning or later in the day after the temperature has reduced.
Water tomatoes deeply at the root zone and avoid splashing water on the leaves.
What to do if your tomato plant has brown leaf edges
Here are a few easy tips to help to tidy up your tomato if it has developed brown leaf edges.
1. Trim off the brown leaves with secateurs
Use sharp, clean secateurs to remove any old leaves that have started to turn brown. Removing old leaves will allow more sunlight to reach the new leaves and the plant will recover quickly.
2. Mulch tomatoes with straw
Surround your tomato plant with mulch to help to keep water in and avoid heavy rain washing the soil away from the roots. You can use straw, hay, shredded paper or cardboard. These light mulches will break down fast and feed the soil bacteria and worms.
3. Water tomatoes regularly
Watering tomatoes regularly particularly in summer is a great way to keep their leaves green and healthy. Water them deeply in summer to make sure they keep their roots moist. Regular water will help to avoid the fruit splitting and to give you larger tomatoes.
For more on why tomatoes stay small, check out my article here: My Tomatoes are Ripening Too Small | 6 Tips for Larger Fruit
4. Use a mild organic fertilizer
Feed your tomatoes in spring with a gentle organic fertilizer. Repeat again at the end of spring. Feed them with a fruit promoting fertilizer instead if you are not getting flowers by the start of summer.
Brown Edges on Tomato Leaves | Summary
Tomatoes can develop brown leaf edges if they are given too much fertilizer, water or develop sunburn. Remove the old brown leaves near the bottom of the stem to tidy up the plant and avoid the leaves touching the ground.