Organic Choice In Weed Killers?

Artificial weed killers are a quick and nasty way to deal with garden weeds. Mix and spray chemical herbicide is a simple "no brainer" solution. An inappropriate import from agriculture direct to the domestic garden scene.

The talk is about protecting children, pets etc... but it is the gardener who mixes and sprays chemical herbicides who is most at risk. Also pond life - frogs, newts etc... are especially susceptible to the ill effects of artificial herbicides.

Sometimes however, there are intractable problems (e.g. weeds among other plants, rock gardens, physical disability, expedience...) that do favour alternative solutions.

Let's look at what does work in organic gardening.

Natural Weed Killers

These are simple substances with a direct and obvious action. They destroy plant life for a short period. They are substances encountered naturally but in small quantities. Their presence is well-known and normally not harmful. But when applied in big doses the results are usually devastatingly obvious in a very short time. Examples include salt, weak organic acids, alcohol, heat from steam, boiling water, and weed flamers.

As always these methods need due caution. But they act at the point they are used and don't enter the food chain. After treatment their damaging effect quickly dissipates. Even the treated plants may sometimes recover.

Acetic Acid Weed Killers

It is made of Acetic Acid (Vinegar) along with other weak organic acids and oils. It has become a 'cottage garden' alternative for those who dislike modern herbicides. Acid is a very blunt instrument, changing the chemistry around roots and in cell sap, to affect the plant in many ways. The damage to plants appears rapidly and even quicker on hot days.

Household Vinegar at 5% acetic acid is not strong enough; 15-20% acetic acid solutions are more effective. Avoid industrial vinegars in the organic garden.

Studies have found acetic acid gave over 90% control within 24 hours of application. With 3 treatments of 20% acetic acid, control remained above 90% even after 9 weeks.

The soil can be acidified but this type of weak organic acid lasts only a few days. That's not long enough to have any lasting affect on earthworms, soil, or organic matter breakdown. The good news is that it won’t cause any insidious harm to pets or children.

Garden products based on acetic acid are now available for organic gardeners as alternative herbicides. It can kill Canadian Thistle, Clover, Dandelion, Foxtail, Ivy Leaf, Milkweed, Pigweed, Poison Hemlock, Ragweed, Quack grass, Bluegrass, plus mosses, liverworts and more. It is not selective and harms the plants it touches.

Fatty Acid Weed Killers

These work by dissolving the plant membranes, making them leaky. The plants dehydrate. Of the 2 products, fatty acids have the edge. They are less broadly harmful, that their soapy properties aid uptake and reduce spreading in the soil.

Obviously you must avoid spraying these on cultivated plants. So it’s probably best confined to spot treatments, perhaps when you need extra help with weed control and to avoid the seriously nasty herbicides.

Remember, if you burn a hole in the lawn with these treatments it is important to fill the empty space as soon as possible. Sow seed and promote strong thick re-growth with the help of organic fertilizers. If your lawn becomes patchy it will become weedier. Always prevent weed seeds being distributed.

Salt Weed Killers

Salt draws water out of cells to leave them dry, and salty soils kill plant roots. So target its application and use sparingly.

Excess salt poisons the soil. Many important organisms: bacteria, fungi, earthworms; will be killed by salinity. It will eventually wash out, even so I would not use it on land intended for cultivating plants. For some gardeners it is an option to consider with drives and gravel areas where plants are not intended to grow and where run off can be contained. Remember, salt will not biodegrade, so regular use will eventually be detrimental to surrounding areas.