Organic Herbicides for the Garden
- Caitlin Youngquist
- 2 minutes ago
- 2 min read
There are four ways we can manage unwanted plants (and bugs) in the garden:
Cultural – reduce weed pressure by making changes in how/where/what/when we plant, and the surrounding environment.
Physical – removing the plant, or creating a physical barrier
Biological – parasitic or predatory insects, or pathogens; or poultry/livestock
Chemical – herbicides (organic or synthetic)
Chemical weed control works in several ways. Keep in mind, these chemicals can be organic or synthetic.
Contact herbicides damage tissues and non-selective (sometimes called "burn-down" herbicides).
Systemic herbicides are absorbed by the plant and are sometimes selective (will not affect all plants equally). Glyphosate is a systemic non-selective herbicide (will kill everything at a high enough dose). 2,4-D is a systemic selective herbicide (will not kill most grasses).
Pre-emergent herbicides inhibit seed germination but will not harm established plants.
Organic herbicides are non-selective and primarily rely on acids (ie. vinegar) and essential oils to damage the leaf cuticle and cause the plants to desiccate and die. They are most effective when the plants are small, and will likely require more frequent use than systemic herbicides. Effectiveness will also vary somewhat by the type of plant (how thick the cuticle is).
You can make organic herbicide using vinegar, soap, and salt or oil.
There are many recipes published on the internet, and a striking lack of consistency! I encourage you to try out one of the basic recipes and see if it works for you. Increase the strength or add ingredients as needed.
The purpose of the vinegar and orange oil are to damage the leaf coating (cuticle) and cause the plant to dry out and then die. This works much better on smaller plants. Some plants may need to be sprayed multiple times.
The dish soap acts as a surfactant to help break the surface tension of the vinegar and spread more evenly on the leaves. The oils acts as an adjuvant to help the water and acid stick to the waxy coating on the leaves. Orange oil also helps strip away the waxy coating.
Primary Ingredients:
Horticultural vinegar (20-40% acetic acid)
Dish soap (acts as a surfactant and helps the acid stick to the leaves)
Orange oil or cooking oil
Table salt or epsom salts (use for driveways/sidewalks, not landscapes)
Miriam Kritzer Van Zant provides 10 different recipes for vinegar based herbicides and notes based on her experience in Illinois. She recommends cooking oil instead of orange oil at a rate of 6 oz of oil per 32 oz of the total mix. This would be a more economical option to try.
Backbone Valley Nursery in Texas prefers this recipe:
1 gallon 20% Horticultural Vinegar
2 Tablespoons Orange Oil
2 Tablespoons dish soap (I think this is too much - try just a few drops to start out).
Carmen Johnson Gardens likes this one. Based on our experience spraying weeds at the compost, this is may be a lot stronger than you need. You could start with 20% vinegar and see how it does.
2 cups Epsom salt
1/4 cup Dawn dish soap
1 gallon of 45% horticultural vinegar
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