When making your own neem insect spray you can adjust the concentration to the purpose and situation.
There are no hard and fast rules, only guidelines.
Some insects are more persistent than others. A preventative neem spray can be weaker than one used for fighting a severe infestation.
For a neem garden spray 0.5% to 1% is a good general purpose solution. Depending on the purpose you may want to increase that to up to 2%.
Use your own observations and common sense. Keep in mind that neem oil insecticide does not kill insects instantly. Wait for at least a week to judge the effects.
For 1 liter of a 0.5 % dilution of neem plant spray you need:
To convert into US measurements:
Five ml make a teaspoon. One litre is roughly a quart
Just multiply these amounts if you want to make a bigger batch. If you want to make a more concentrated batch multiply both the amount of neem oil and the amount of soap used:
For 20 liters of a 1% solution of neem insect spray you need:
If you have trouble dissolving the oil, use more detergent.
Spray the neem insecticide solution on all the leaves, especially the undersides where insects like to hide. If you have plenty drench the soil around the roots as well. It does not hurt, neem oil is actually good for your soil.
Use your neem insect spray as quickly as possible, definitely within eight hours. Once your batch neem garden spray is mixed the neem oil starts breaking down. Always make a fresh neem insecticide batch for spraying, and only prepare the amount you need.
How often should you use neem garden spray? The suggestions below are general guidelines. Keep a close eye on things and fine tune as needed. If you are worried about sensitive plants, spray just a little bit in a small area, wait for a day or two, and see what happens. If you use insecticidal soap you should not have any problems.
Neem plant spray as a preventative measure: Spray once a fortnight using a 0.5 % solution. This should prevent any insect problems in the first place.
Neem insect spray to fight an infestation: When spraying the first time throroughly drench al leaves and the soil around the plant. Then spray once a week until the problem disappears. If it rains you may need to respray sooner. If you are dealing with a less sensitive insect species you may need to increase the concentration of the neem spray. See how you go.
Learn more about making, using and buying neem insect spray.