Typically, a weed is a plant in a place not intended. Not all weeds are foreign invaders; I will admit to introducing aggressive, vigorous growers to my garden. Although native plants can be prolific to a fault, this usually happens when the growing conditions are improved and competition is suppressed. For instance, a beautiful and fragrant perennial wildflower to the Texas Panhandle region, Berlandiera lyrata, chocolate flower, can be a nuisance in a garden with too well amended soil and even medium water-use, growing to double or triple its normal height, re-seeding with abandon. In its native surroundings, in un-amended soil and local rainfall, it displays a compact, disciplined, restrained form. It's many seeds either fail to germinate or are eaten by wildlife. Likewise, plants that are considered to be invasive or nuisance plants in one region of the country are fairly constrained in another where growing conditions are much less favorable.
The fact is, most gardeners don't like weeds, whether native or non native. We might not even care for "volunteers" from our chosen plants springing up where they may. We want the plant out.
Weeds require the same elements to grow as our landscape plants: light, water, nutrients and space. At least one of these elements needs to be denied to the weeds to stop the cycle. The most problematic weeds are those that require very little light, water, nutrients or space to grow -- perennial problems of the worst sort.
There are many ways to rid the garden of weeds. Being ecologically friendly, and wanting to follow the principles of Integrated Pest Management, or Integrated Problem Management, as I call it, I consider the use of any chemical herbicide a last resort practice. (Certified organic operations must comply with the rules and regulations of the National Organic Program and the National Organic Standards Board which does not allow use of synthetic chemical herbicides, pesticides, fungicides and miticides.)
In implementing the practices of IPM, let's look at the decision to weed the garden as an example. The steps of observation, recognition and assessment of the situation, evaluation and monitoring should be carried out before choosing a management technique. These are some of the questions that may come to mind during these first three IPM steps.
- Why do you have a weed?
- Can we prevent the weed in the first place?
- Was there space for a weed to germinate and grow? Are there bare spots in the turf?
- Is the mulch thick enough? Re-seeding with turf grass seed may be the solution (for a lawn), leaving no space for weed seeds to germinate.
- Is the soil healthy enough to support the preferred plant in that location? Does one need to provide better living conditions for our chosen plants to out compete weeds?
- Have weed seeds been dredged up as a result of disturbing the soil through soil amending, planting or even pulling a weed?
- Did the weed seed blow in from a neighbor's or a vacant lot? Did bindweed move in from the alley? The invasive, noxious weeds certainly earn their reputation. We are powerless to prevent all problems.
There is a process to weed problem management. In the process of using IPM,
- Deciding if the weed is a problem is the first step. Assess the situation. If it is not acceptable to you that even a new emerged weed be present in the landscape, start looking over the options.
- Have all the correct cultural practices been implemented in the landscape such as the use of mulch, efficient watering by drip system, watering only the plant, not the entire bed?
- Could a natural pre-emergent such as corn gluten meal be used? To control future spreading of weeds, do not let weeds seed out. Do not compost the seeds of weeds, just dispose of them.
- You may decide to jump to the second level: mechanical control (sometimes referred to as physical control) and handpick the weed, cultivate the ground to uproot the weed, use weed flamers, dousing the weed with boiling water, or cutting off the weed just below ground level. In some cases, soil sterilization with the application of heat or steam is used (however, the cost may be prohibitive). Soil solarization is used in soils with considerable weed and pathogen problems.
- If the weed is bindweed, a slow biological method might be used, such as the bindweed mite.
- You may choose to use the highest level, the chemical level and spray the weed with a soil-safe 20% vinegar solution or other organic chemical herbicide. There are two levels of chemical control, using organic and synthetic chemicals. There are several organic herbicides, available, even locally. Products labeled with the OMRI (Organic Materials Review Institute) seal are considered safe for organic operations. To check a product, look for the OMRI seal, or check the OMRI Database. Most are a combination of acetic acid (vinegar) and citric acids, clove and thyme oil and other ingredients. Organic herbicides are best used when the weed is small; several applications to larger weeds may be necessary.
- The step of last resort is using a synthetic chemical herbicide, often with residual value, and harmful to the soil life (depending on the herbicide).
Some Consequences of Weeding Techniques
Even pulling a weed involves making choices. Each of your actions has consequences beyond just ending the weeds life. If you don't determine the best appropriate cultural management technique to apply to the problem, the problem will re-occur and you will be faced with jumping to the second or higher levels again in the future. Below I've listed consequences of common weed control methods.
- Pulling out the weed could bring up buried weed seeds.
- Cultivating could bring up weed seeds, contribute to a loss of soil moisture, and perhaps destroy roots of vegetables and other ornamentals close by.
- If you decide to pull out the weed you might also choose to prevent disturbed weed seeds from re-emerging by applying corn gluten meal (an organic pre-emergent) to that spot.
- Applying boiling water may harm adjacent plants and microbial life.
- Using a weed flamer may cause a fire if care is not taken. Flamers are generally ineffective against grasses because their growing point is underground.
- Using biological agents takes time. The weed infestation may worsen before it diminishes.
- Applying a chemical remedy, such as the non-selective 20% vinegar solution, even though organic, may damage nearby plants if the spray isn't applied accurately. Even a low breeze causes drift.
- Synthetic chemicals carry the greatest potential for harm to other plants, micro and macro organisms, even humans.
Organic Weed Control Methods
Weeds happen! The subject of organic weed control has been studied in depth with numerous practices advanced to help farmers and vegetable producers combat this serious problem. Certified organic operations are not permitted use of synthetic chemicals, and the Organics Material Review Institute (OMRI) must certify any organic chemicals.
Hand weeding is often not economically practical in large scale vegetable operations. There is a plethora of information today on the Internet to help gardeners and growers tackle the problems of weeds in an ecologically friendly manner. Weed Management for Organic Crops Paper a University of California paper, Publication 7250, and Ten Steps Towards Organic Weed Control, by Vern Grubinger, Vegetable and Berry Specialist with the University of Vermont Extension offer many practices in use today.
Many of these practices can be used in the home landscape and vegetable gardens on a smaller scale, where practical. Briefly, some of the methods suggested by these two papers are:
- Reduce the weed seed bank in the soil to reduce the need for cultivation. Weeds produce thousands of seeds; their seeds can remain viable for years.
- Thoroughly compost animal manures to kill weed seeds ensuring the proper temperature is reached and maintained long enough.
- Pre-germinate weed seeds prior to planting. Shallow till or disturb the soil; water thoroughly to promote weed germination and growth. Till and water again to kill the weeds and germinate remaining weed seeds before planting the crop.
- Mow alleys and edges of fields to keep weeds from going to seed and blowing in.
- Power wash equipment to prevent spread of weed seeds.
- Diversify crop rotations to keep particular weeds from multiplying.
- Use cover crops to compete with weeds. Cover crops tilled in enriches the soil as well.
- Feed the crop, not the weed by changing organic fertilizer placement and timing.
- Be selective in the cultivating tool used. There are many more different types of cultivators available today than just 10 years ago.
- Combine tools to cover different crop zones. This includes flamers, blind cultivators, etc.
- Time the cultivation to shallow cultivate weeds while they are small before the cash crop emerges. Larger seed crops like corn are planted deeper and are not affected by shallow cultivating.
- Experiment with different weed management techniques to find what works best for the crop.
- Use corn gluten meal as pre-emergent control. Use only outside the crop germination period.
- Use mulch to suppress weeds and drip irrigation for irrigating only the cash crop.
- Never let the weed grow and produce more weed seed.