In this podcast, we talk organic weed control with Dr. Jeff Gillman. While currently the Director of the UNC Charlotte Botanical Gardens in Charlotte North Carolina, he’s spent his career getting to the truth behind the rhetoric in matters involving both the garden and the environment.
Jeff holds a master’s degree in entomology and a Ph.D. in horticulture. He has worked as a Professor at the University of Minnesota where he taught and conducted research on a variety of horticultural topics including extensive work on organic weed control.
Organic Weed control is a never-ending battle no matter how you slice it. For organic gardeners, the finding methods to control weeds without the use of harsh synthetic chemicals has always been rather elusive.
However, one control method to fight broadleaf weeds in lawns and landscapes is an iron chelate product that is readily available in retail lawn and garden centers. The active ingredient is FEHEDTA and is marketed under several brand names. See the link towards the bottom of this post for more information and product names.
It’s often used as an iron fertilizer. When applied as an herbicide, the control overdoses broadleaf weeds with iron.
A common synthetic herbicide commonly used in lawns for broadleaf weed control contains an active ingredient 2, 4-D. The biggest concern Jeff cites in its use is the length of time is stays in the system of animals and pets.
For organic pre-emergence weed control, the only option currently is corn gluten meal. While it can be very effective under optimal conditions, consumers will get mixed results depending on where you live in the country.
A side benefit to using corn gluten meal is that it supplies enough fertilizer to feed your lawn for a year. The downside to corn gluten is that it is not very effective in the first year of use but the second year, and beyond, it controls about 80% of broadleaf weeds.
To be effective, you must use at 20 pounds per thousand square feet. It’s very safe and the only organic pre-emergence weed control currently available.
As for landscape beds and gardens, two of the best options currently available are:
Common vinegar (acetic acid) when topically applied, burns the tops but has little impact on roots. Be careful using this as it is deadly to frogs and amphibious creatures. Horticultural grade acetic acid is dangerous at 20% concentration. Jeff advises not to use it. It’s too dangerous and simply not worth the risk.
Clove oils and citrus oils are also sold as organic alternatives to synthetic herbicides. Their killing action is similar to vinegar and provides marginal success to weed control. If using any of the above options, it’s best to attempt control when weeds are young and small.
Flame Weeders, typically use propane canisters or backpack tanks to deliver a concentrated flame to weeds. To be effective, it often requires multiple applications. The heat only penetrates about ½ inch into the ground.
If you’re looking for total control with any of the above options, you’ll likely be disappointed, at least after only one application.
My protocol for a weedless organic lawn and landscape
Although my lawn may look weed-free, it’s not. But weeds are minimal. I attribute that to focusing on building the soil health and promoting the growth of the lawn for ideal conditions: mowing high, aerating the soil in fall, adding composted manure and Milorganite. Also, note the use of mulch in the landscape beds. Between the beds and the lawn, overall my weed challenges are minimal in my 3-acres of cultivated space.
The best organic method for controlling weeds in landscape beds is the generous use of natural mulch combined with dense plantings. I apply a two-inch layer of free arborist wood chips (or purchased natural mulch as above) over all exposed surfaces.
The difference in areas where I have mulch and where it needs to be added is dramatic. Weeds are few and far between in the mulched areas, vs. a constant battle in the exposed areas. If you need to be convinced that mulch works for suppressing weeds, try this experiment for yourself, and you’ll quickly become a fan of using mulch to control weeds naturally.
Even with the liberal use of mulch, weeds are a fact of life. Over the years, I’ve finally settled into a single tool I use nearly all the time for weeding my garden beds.
I’ve heard it referred to by several names, primarily the scuffle hoe (aka winged weeder). It allows me to easily sever roots from the top growth at the soil surface. I like it because I can stay in a standing position while slicing weeds from their roots with minimal effort.
The key to making this my tool of choice is finding the one with a high quality, sharp stainless steel cutting edge on all three sides. That, combined with a long handle which (for me) meets me at about my belt line.
For you, a higher angle of attack may be easier to work with. Personally, I’ve used ones like that where they meet my body at about mid-chest level. I don’t find those nearly as easy to use. Being able to keep your arms in a more relaxed, extended position is what I’ve found to be the most comfortable and effortless option.
Solarization is another method for killing weeds and weed seeds near the surface. Clear thick plastic placed over the soil surface and left in place for several weeks can be effective.
One of the temporary downsides of solarization is the loss of beneficial microbes living near the surface. Fortunately, once the plastic is removed, microbes will repopulate the area within just a few weeks.