Tomato Leaf Insecticidal Soap Spray

The Science Behind Tomato Leaf Spray

Tomato plants belong to the nightshade family (Solanaceae) and produce natural defense compounds called alkaloids — specifically tomatine and solanine. These compounds:

• Are toxic to many soft-bodied insects
• Act as feeding deterrents
• Disrupt insect digestive systems

By extracting these alkaloids into a spray and combining them with insecticidal soap, you create a dual-action treatment that kills on contact AND deters future feeding.

Why Use Tomato Leaves?

If you grow tomatoes, you’re already creating this ingredient for free every time you prune! Instead of composting those suckers and lower leaves, turn them into pest spray.

Best leaves to use:

• Suckers removed during pruning
• Lower leaves removed for airflow
• End-of-season foliage when pulling plants

Don’t use:

• Diseased leaves (could spread pathogens)
• Leaves treated with other pesticides
• Very young seedling leaves (not enough alkaloid content)

Instructions

Step 1: Make Tomato Leaf Tea

1. Chop 2 cups of fresh tomato leaves roughly
2. Place in a heat-safe container
3. Pour 2 cups of boiling water over the leaves
4. Cover and steep for at least 4 hours (overnight is ideal)
5. Strain through cheesecloth, pressing leaves to extract all liquid

Step 2: Mix the Spray

1. Pour the strained tomato leaf concentrate into a spray bottle
2. Add 1 tablespoon of castile soap
3. Add enough water to make 1 quart total
4. Shake gently to combine

Step 3: Apply

• Spray leaf undersides and stems where pests congregate
• Apply in early morning hours for best results
• Avoid spraying on edible parts of plants close to harvest
• Reapply every 5-7 days

Effectiveness

Pest	Effectiveness	Mechanism
Aphids	★★★★★	Contact kill + feeding deterrent
Whiteflies	★★★★☆	Contact kill + moderate deterrent
Small caterpillars	★★★☆☆	Digestive disruption
Spider mites	★★☆☆☆	Limited — use neem oil recipe instead

Storage

Unlike most insecticidal soap mixes, the tomato leaf concentrate stores well:

• Concentrate (before adding soap): Up to 1 week refrigerated in a sealed jar
• Mixed spray: Use within 24 hours

This is a practical advantage — you can make a batch of concentrate on the weekend and use it throughout the week.

Safety Precautions

⚠️ Tomato leaf alkaloids are mildly toxic to humans and pets.

• Wear gloves when handling concentrated tomato leaf tea
• Wash hands thoroughly after mixing and spraying
• Don’t spray on leafy greens you’ll eat raw within a week
• Keep concentrate away from children and pets
• Compost used leaves rather than leaving them accessible

The alkaloid concentration in this spray is low enough that it’s safe for normal garden use, but treat it with more respect than plain soap spray.

When to Choose This Recipe

✅ Great for:

• Gardeners who already grow tomatoes (free ingredients!)
• Organic gardens where you want plant-derived pest control
• Aphid problems on ornamental plants
• Combining with other methods in an IPM strategy

❌ Skip this when:

• You don’t have access to fresh tomato leaves
• You need to treat edible plants close to harvest
• You’re dealing with hard-shelled pests (try the alcohol formula)
• Your primary concern is spider mites (choose neem oil instead)