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Weed Free Organically

By Jay White
Freelance Writer

Four years ago, I went to war! Weeds in my vegetable garden and flower beds were sucking all of the joy out of my gardening experience. So, in 2006 I declared war on my weeds.

When I started my current garden, I decided that I would do everything possible to be an organic grower. At that time, I did not fully appreciate how difficult weed control can be for the organic grower. Within three months of tilling up a portion of an old coastal field of Bermuda grass in Washington County and planting my first fall garden, I was already losing the war to the weeds. Out of frustration, I began to research organic weed-control methods. Due to this research and much experimentation, I have now developed an integrated weed control program that has greatly reduced the amount of time I spend bent over in my gardens. My integrated weed control regime consists of “Four P’s”: preparation, pre-emergent tools, post-emergent tools and persistence.

Preparation
Organic growers do not have access to many herbicides that are as effective as something like RoundUp, so it is important to do everything possible to kill or remove as many weeds as possible before any other organic weed-control methods are applied. Proper bed preparation is the critical first part of an integrated organic weed-control program. The following activities are effective organic options.

Solarization — Solarization is a process in which clear plastic is laid over an area of weed infestation. The clear plastic allows the sun’s radiation to raise the temperature in the air gap to a level that will “cook” any seedlings that dare to emerge. When I get ready to prepare a new bed, I mow the vegetation very close to the ground and then water it thoroughly. Then I spread a sheet of 4- or 6-mil polyethylene over the area. Once this is down, I secure it with either soil, lumber or old bricks. It is important to get a good seal all around the plastic. You don’t want any of the hot air escaping. Then, depending on the season, I walk away for three to six months and let the sun do the rest.

Solarization has been very effective for me. Once I remove the plastic there is nothing growing. Nothing! All that is left is a bunch of dried brown plant material. I till this into the soil and the new bed is ready for planting and/or other weed-control measures.

Smothering — Smothering kills weeds by depriving them of both light and water. The process I use for smothering is very similar to the solarization process. Before I lay down my smothering material I mow, chop or hoe the existing weeds down to the ground. Smothering will work fine without mowing if your smothering material is heavy enough to push and hold the existing plants down.

I have used many different things as smothering agents. Any opaque material will work, but my favorite is plywood or HardiePlank. Both of these materials cover a large area and weigh enough that they will not be easily blow away. Tarps and black plastic are effective if you take the time to properly anchor them. Wind is a real enemy of these two. No matter how well I anchor them, the wind always seems to find a way to uncover everything I have tried to cover up.

Newspaper is also an effective smothering agent. Not only does it suppress weeds, it breaks down and becomes additional organic material. Newspaper is thin and fragile, especially when wet. Because of its light weight, it is difficult to keep in place. I only recommend using newspaper in combination with mulch or in a small area that has some protection from the wind.

When using newspaper, I lay down about eight overlapping layers. I use newspaper and hay in the walk paths of my row garden. I re-apply this treatment every spring and fall. My row garden really is in the middle of an old coastal field and this combination of hay and newspaper does a very good job of keeping the weeds in my paths at bay.

Pre-emergent Methods
Once a bed has been sterilized through either solarization or smothering methods, it is time to stop the weed seeds that survived from germinating. Mulch and corn gluten meal are two of the most common pre-emergent weed-control weapons available.

Mulch — Mulch is the organic gardener’s manna. In addition to providing pre-emergent control, mulch conserves water by reducing evaporation and runoff. It also keeps roots cool in the summer and warm in the winter. On top of all of this, mulch provides organic material to the soil as it breaks down. In my opinion, mulch is the premier, pre-emergent weapon in the organic gardener’s arsenal.

Mulch works by depriving weed seeds of the light they need to germinate. I have done some experiments in my own beds and I have found that a 6” layer of hardwood mulch yields the best control. When I get ready to mulch a new bed, I always put down newspaper first. The newspaper adds one more layer of light suppression that I have found to be very effective. When mulching a pre-existing bed, I simply add more mulch on top of the old, existing mulch.

I get my hardwood mulch from the Brenham landfill. Most municipalities sell mulch and compost. If you have a truck, this is the way to go. I get my mulch for a penny a pound. That is just $12 for one cubic yard of mulch (approximately 1,200 pounds depending on moisture content). At that price there is no reason not to mulch.

Even though I now use hardwood mulch exclusively in my flower beds, there are many other products out there that will provide the same level of suppression. In previous gardens I have used cedar bark, pine bark, pine needles, grass clippings and hay. There are countless other varieties available as well. Experiment with different things and you will quickly discover what works best for you.

Mulching is not something that can be done only once. Mulch is (usually, not always) an organic material. As such, it breaks down and turns into compost. Because of this, it becomes a great landing spot for airborne weed seeds. To reduce this, I mulch everything twice a year.

Corn Gluten Meal — Corn Gluten Meal (CGM) is a by-product of the corn milling process that has certain properties that make it effective as a pre-emergent herbicide. CGM contains proteins that inhibit root growth in newly germinated plants. There really is no downside to this organic weed control weapon. It is completely non-toxic (you could eat it, if you needed to), it controls weeds and it acts as a fertilizer. An application of CGM is the organic equivalent of a formulated 10-0-0 fertilizer found at garden centers.

Recent experiments at Texas A&M by Joe Masabni, Ph.D., Extension vegetable specialist, and Patrick Lilliard, Extension specialist, have shown that CGM is a very effective pre-emergent when applied at the proper rate and at the proper time.

For their experiment, four 8’ x 8’ beds were prepared by manual means. Each bed was sub-divided into four 2’ x 2’ beds. These sub-beds were randomized and each contained one control block. The other 3 blocks received one, two or three applications of CGM at a rate of 5.12 oz/block. This is equivalent to a field application rate of 80 lbs/1,000 sq. ft. At the end of the experiment, all plant material was removed at soil level and weighed and compared.

According to this experiment, a single application of CGM reduced broadleaf weeds from 9.69 g in the control block to 1.2 g in the other blocks. This is equivalent to an 88 percent reduction. A single application of CGM was not very effective against grasses. Grass control required a second application two weeks after the first, and a third application two weeks after the second. By applying CGM three times over a five-week period, grasses were reduced from 4.91 g to 0.29 g, or a 94 percent reduction. Broadleaf weeds treated over the five week period were reduced even further to 0.07 g or a 99 percent reduction.

As this experiment shows, CGM is an effective pre-emergent herbicide in a homeowner’s garden. CGM has gained much popularity and is easy to find at most garden centers. Most box stores and nurseries also carry it.

It is important to note that CGM is only effective as a pre-emergent. Once weeds have germinated (even at the seedling stage) or became established, CGM has no measureable affect as an herbicide. In fact, the nitrogen in the product can actually accelerate the growth of the weeds.

Dense plantings — Sometimes we cause our own problems. Traditional planting methods have us tilling up long straight rows with walk paths between them. The war of the weeds is usually lost in the pathways between the rows. One way to reduce this issue is to change the way you raise a garden. Lay out your beds in squares and plant your crops as close together as you can without harming production. Dense plantings choke out weeds by limiting the light available to them. Close plantings in square beds provide the same square footage of production with fewer paths.

Post-emergent Methods
Most gardeners I know hate to pull weeds. That is why an integrated program is so important. Persistently applying the “Four P’s” will greatly reduce the amount of weeds that require manual removal.

Pulling — I have two very different vegetable gardens at my house. One is a traditional row garden and the other is a raised-bed garden. Hand weeding of the row garden is not practical or effective; there are just too many weeds. On the other hand, my raised-bed garden was designed and built with the “Four P’s” of weed control in mind. Because of this, there are few enough weeds there that weeding by hand is an effective tool.

When pulling weeds, strive to remove them before they set seed. An old garden adage is, “One year of seeding equals seven years of weeding.” So, pull weeds when they are young and never ever let them set seeds. If weeds are pulled in their immature form, they can go directly into the compost bin with no worries.

Also, to increase the effectiveness of my hand weeding, I always use various tools to assist me. A garden trowel, a large screwdriver and a meat fork are great tools that help me remove weeds, roots and all.

Vinegar — Vinegar (or acetic acid) is an effective post-emergent herbicide that works by removing the waxy covering from plants. Removing the cuticle from the plants allows them to “transpire” themselves to death. Common household vinegar (5 percent acetic acid) can be effective (especially if combined with a little dish soap and little rubbing alcohol), but real killing power resides in the more concentrated forms found at garden centers.

Acetic acid is available in concentrations up to 20 percent. Concentrated acetic acid is quite effective on a wide range of both grassy and broadleaf weeds. I have seen dandelions and crabgrass begin to wither 30 minutes after the initial application. Vinegar is best when applied to young plants. Established weeds may need a second or third application to finally kill them.

Be careful when applying vinegar. Overspray can kill things you don’t want to die. I use a spray bottle and a shield when spraying close to my desirable plants. If you want to spray a wide area, then a pump sprayer works well, too.

Hoeing — A sharp garden hoe is an effective post-emergent weed control agent. Hoeing is much faster and less physically demanding than hand weeding. A good sharp hoe can quickly clean up a lot of space. I use the hoe frequently in my row garden. Hoes are not effective against plants with a deep tap root. Wild carrot and dandelion are particularly noxious weeds with deep tap roots. Chopping these off at the surface only slows their growth and they are bound to return.

Burning — My favorite organic post-emergent weed control weapon is fire! I use a small hand held propane torch to scorch weeds to death. You do not have to “burn the plant up” for fire to be effective. I simply scorch the plant by running the flame up and down its length until there is a noticeable change in its structure. This is usually enough to kill it all the way down to the roots. One word of caution, some desirable plants are very sensitive to high heat, so avoid burning weeds that are too close to the vegetables or flowers.

Boiling water — I know several people that swear that boiling water is a great weed killer. The heat from the boiling water is supposed to kill the weeds. I have seen some limited success when applying boiling water to young plants. Unfortunately, 212 degrees is just not hot enough to kill most established Texas weeds.

Persistence
I have accepted the fact that there is no such thing as a weed-free garden. I use all of the methods described in this article and I still have weeds. However, I have much fewer weeds today than I did four years ago. The “Four P” approach to organic weed control has reduced my weed populations to the point that I no longer consider them my single biggest problem.

Through the persistent use of preparation and pre-emergent and post-emergent tools I am slowly winning the war of the weeds. I have now had enough success with the “Four P’s” to believe that if I just stick to it, I might actually get to fully enjoy my garden as the years go by.

Jay White is a full time computer specialist for the M.D. Anderson Cancer Center in Houston, Texas, and he is completing an M.S. in Horticulture at Texas A&M. In his spare time he gardens and maintains “The Masters of Horticulture” blog at http://yupneck1.wordpress.com/.

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