The advice on horticultural vinegar presented below is republished with permission by Miriam Kritzer Van Zant, President/CEO of Community Conservation Botanical Garden of Southern Illinios. You can reach Miriam and the Botanical Garden at email@example.com with questions about this recipe and what works in your locality.
This is Part 2 of a 2-part series on on using horticultural vinegar. It gives instructions and formulas for making herbicides and includes new formulas which work in acidic wetland soils. Part 1 explains the reasons to use horticultural vinegar, why new formulas are needed, and considers other relatively non-toxic methods of weed control.
Put on protective gloves and eye protection to handle strong vinegar. It is dangerous to get directly splashed in an eye. In case of getting it on you, rinse off with cool water as soon as possible. You may wish to drink water before and after handling concentrated vinegar to offset the drying effect on the throat.
For mixing herbicides, gently pour vinegar, dish soap and additives of choice together, and either mix them with a stirrer, or also securely cap the mixing bottle and shake the ingredients together. For larger batches, use a funnel to pour mixed vinegars back into the same bottles for storage. Mark them as pre-mixed, and what you've added. Pour into 32-oz hand sprayer bottles, or other sprayer. Write down your formulas elsewhere as well.
The defoliant solution may soon smear what was written on storage bottles. Wear protective eyewear, such as sunglasses or goggles during application. Set the sprayer to a gentle fine mist. Later in the season, additives may become increasingly important, as plants can thicken waxy cuticles on mature leaves.
Spray the solution directly on leaves, from a few inches away. Include undersides if you can. Reapply as needed. Be careful about getting defoliant on the wrong plants, or of it splashing back at you. Exposure to small amounts of residual spray may wilt part of a leaf but will rarely permanently damage neighboring plants, so no need to panic if a little gets on a plant you want to preserve. You may want to rinse a neighboring plant if you’re really concerned about residual spray. I’ve never needed to.
Rinse off and store sprayer heads separately from bottles between uses. Having a spare spray head will get you through the moment when the other sprayer head eventually fails.
• 2 or more spray bottles
• 2 or more spray heads to fit the bottles
• dish soap caps to close spray bottles between uses
• funnel to fill bottles
• pail or empty gallon container for mixing larger batches
• stirrer for larger batches
• measuring spoons for adding herbal oils
• measuring cup in case increments are lacking or hard to read on the spray bottles (optional)
C1-C10 are explained below:
• 30% vinegar- use as half or more of total
• C2 dish soap 1-2 Tbsp depending on other additives
• 5% vinegar to top off mixtures
• C1, C3 cooking oil
• C1, C4 orange oil or orange oil soap- 2 Tbsp/32 oz
• C1, C5 unadulterated alcohol, vodka or gin 2 Tbsp/32 oz
• C1, C6 14% citric acid powder or 12% lemon juice
• C1, C7 clove oil
• C1, C8 molasses or yucca extract (probably agave syrup)
• C1, C9 RARELY USE epsom salts
• C10 NEVER USE sodium chloride
Comments on Ingredients
C1 is optional.
C2 - use a liquid, biodegradable, low-phosphate soap, like Ecos Dishmate® or Dawn®, or any similar soap that suds well.
C3 Cooking oil can be fresh or rancid. Oil can be previously used for cooking, then strained through a coffee filter. Cooking oil is usually less expensive to use than orange oil or any of the herbal oils. Oils that are hard at room temperature, such as coconut oil, palm oil, cocoa butter, lard, Crisco and others containing cross-linked fats are unsuitable as they will likely clog the sprayer.
In our preliminary experiments, 10 oz of oil was too much for 32 oz total, and even seemed to provide protection to some leaves while simultaneously wilting other leaves quickly.
Four oz of oil was too little for 32 oz total as it took a couple of days for leaves to wilt as well as with 6 oz. That longer wilt time rendered the spray ineffective on many leaves, if it rained during the period between application and wilting. It may be that some other amount between 4 and 10 oz is even better than 6 oz, and this may change during drier weather or for different conditions and target weeds. Please let us know.
Six ounces of cooking oil per 32 oz total has worked the quickest so far, during breaks in rainy weather. After a couple of weeks with no rain, it seems this same formula does not wilt as quickly as it did during wetter periods. However, the few surviving plants only continued to grow very slowly. Perhaps the oil formulas are more strongly tied to rain or higher water tables or other moisture than some other formulas, as previously mentioned.
Please remember, this is all still preliminary research. When there is a conservation botanical garden in southern Illinois, with full time staff, it will be a good place to run statistically significant double-blind trials on different vinegar defoliant formulas under varied conditions.
C4 Orange oil or orange oil soap were good additives though cooking oil (see C3) is cheaper to use.
C5 Alcohol can be grain alcohol, sold at liquor stores and some grocery stores. Please don't spray isopropyl rubbing alcohol on your garden. Rubbing alcohol sold in drug and grocery stores contains toxic adulterants to keep people from drinking it, including acetone, denatonium benzoate, and methyl isobutyl ketone. These are not appropriate for any gardens, let alone organic ones.
I tried grain alcohol once as an additive but it was during a period of heavy rain and didn't work as well for me as the oil formulas. Naturalist Charlie Pitts told me he swears by a vinegar-alcohol formula effectively used for poison ivy in Belleville, IL, so it is given below. He may be working in soils that are a little less acidic with a lower water table than where I experimented in southern Illinois.
C6 I've only tried citric acid with 5% vinegar, and found that ineffective against poison ivy. It may work well with stronger vinegar as citric acid increases acidity. Lemon juice has citrate in it, though it is more expensive to use than citric acid powder. Higher acidity can be an issue for alkaline soils, like those common in central and northern Illinois and in some wet areas such as Florida. Southern Illinois soils are mostly acidic to begin with. Many garden vegetables and flowers prefer soils with some acidity.
C7 For clove oil or any appropriate herbal oil try starting with 2 Tbsp/32 oz and adjust it from there.
C8 Molasses or yucca syrup help plant leaves take up the mixtures. Their use is probably less of a good idea in a wet environment like southern Illinois, as molasses and other sugars also feed plants and plants may recover quickly from wilting under wet conditions. They are included in MaestroGro’s formula which was taken off the market because of pesticide licensing issues.
Honey, molasses and other sweeteners, diluted well, can be sprayed on compost piles, to speed up bacterial action. Raw organic honey especially was recommended for this purpose by Gorden Montgomery, owner of Agri-Life in Goreville, IL. Dilute the honey or other sweetener to 3% and spray your compost pile.
C9 Epsom salts consist of magnesium sulfate which binds calcium and other minerals in soils for years. Sulpher can also cause problems in soils (see FAO report link under C10). I was able to drop orange oil or orange oil soap and epsom salts after adjusting the amount of cooking oil that I was using. You may see epsom salt recipes or need to add magnesium to a small group of specific crops. I decided after much internal debate to finally offer my epsom salt recipe improved for effectiveness in southern Illinois below, as an organic asparagus grower had requested it. Any defoliant would have to be used before asparagus emerges in the spring. However, please use the other recipes instead unless you know you need to add magnesium to a crop. Also see orange oil (C4 above) and the epsom salt recipe below.
C10 Please, never use sodium chloride on soil. Earlier civilizations salted the soil of enemy civilizations so they could not rise again. There are several parts of the world today that have soil problems as a result of human activity resulting in salt deposits on soils, and/or accumulated natural saline deposits. More on the effects of salt on soil:
Miriam Kritzer Van Zant's July-August 2017 best defoliant recipe
Tested for poison ivy in southern Illinois
Per 32 oz bottle:
• 16 oz 30% horticultural vinegar
• 6 oz cooking oil- see C3 above
• 2 full Tbsp Dishmate dish soap
• 8 oz 5% vinegar
Fill a 32-oz sprayer with the above ingredients, shake just before spraying. Apply on dry days, or within a few hours of rain as it wilts leaves quickly. Check again for the next two days for newly opened leaves and spray those as well. Check again and spray if needed every few weeks. The amount needed, if any, will be reduced each time. I now mix four 32 oz bottle at a time and leave them capped and ready to go.
Only for use in beds for magnesium-loving perennial plants like asparagus
• 1⁄2 cup epsom salts MgSO4
• 1 Tbsp Dishmate dish soap Either
• 2 cups 20% vinegar plus
• 2 cups 5% vinegar OR 1 and 1/3 cups 30% vinegar plus 2 and 2/3 cups 5% vinegar
My epsom salt defoliant recipe was based on two internet recipes: Lifehack's weedkiller aka 'Weed B Gone' and Mark Thomas Builder's recipe with stronger vinegar than Lifehack recommended. I had been using Maestro's 20% vinegar when developing this recipe so offer it for 20% or 30% vinegar.
Neither of the internet recipes I started with worked as well in southern Illinois against poison ivy as my own epsom salt blend. Recipes using only weak vinegar probably only work in very arid climates or with much lower water tables.
Recommended for use against poison ivy in Belleville, IL
For 32 oz bottle:
• 2 Tbsp grain alcohol, gin or vodka
• 1 squirt (1-2 Tbsps) dish soap
• 20% vinegar to fill (or 10 oz water and 20 oz 30% vinegar)
• Maestro's Blackjack21
• 1 gallon 20-21% vinegar
• 10-12% (12.8-15.36 oz) molasses
• 1-2 oz (1.28-2.56%) orange oil
• 1-2 oz dish soap
Maestro sells 20% vinegar out of Texas. They had a mixture called Blackjack21 that they took off the market as they ran into problems with herbicide distribution licenses. Now Maestro sells plain 20% vinegar and shares their recipe. Blackjack21 works in southern Illinois but not as quickly or as well as my own recipes, above.
Diluting Blackjack 21 50/50 with 20% vinegar helped. However, even the 50/50 dilution still took about 24 hrs to wilt poison ivy leaves in southern Illinois in years with more normal rainfall. It only took my above oil recipe a few hours to wilt poison ivy leaves in 2017 between rains. The Maestro recipe is reported to work well in Texas. Similar recipes have been given good reviews for Australia.
Effective weed control has also been reported in these places with 10% vinegar. However, in my experience 10% is too weak for southern Illinois, with its frequent rain and high water tables.
The Blackjack21 recipe is a good example of how to use some of the other additives from the list above, and may be good for some gardens in drier areas such as those in higher altitudes. Maestro has several interesting natural gardening products.
CCBGSI did better with 30% vinegar from a different distributor, as shipping costs are the same for both strengths. Maestro is acknowledged for their pioneering work with horticultural vinegar. It is hoped they continue to do well in their part of the United States.
CCBGSI is asking you to experiment to find the best formulas for your property, conditions and target weeds, and to share that information with the rest of us. Please send your best effective formulas to firstname.lastname@example.org. To join the CCBGSI mailing list, donate to CCBGSI, or for information on obtaining horticultural vinegar via donation to benefit CCBGSI, please send an inquiry to the e-mail address above.
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