Gardening: Know your chemicals

  • May. 18, 2017 12:30 a.m.

By definition weeds are plants out of place which includes plants that have come from parent plants within the garden as well as the plants that develop from seeds that arrive via animals, shoes, vehicles or the wind.

Annual weeds grow quickly and typically have a small root system making them easier to pull. Their life cycle starts as a seed or a piece of plant and ends once seed is produced. Annual weeds can usually be eliminated if they are removed before they go to seed. Note that a number of annual weeds overwinter as immature plants and are quick to grow in spring.

Perennial weeds are harder to eradicate. They have a larger root system and many of the weeds will regrow from small sections of the roots.

English gardeners have hand dug their plots for centuries, removing roots and root pieces as they go. Being persistent and removing all green parts of the plants as it appears will eventually starve the root causing the plant to die. The downside is that hand digging is hard work and the soil should not be dug when it is wet.

Cultivating or rototilling empty areas to keep the garden black can starve unwanted plants. The downside being that the weeds roots will get cut up and develop into new plants. Like hand digging, the soil must be dry and the weeds must be tilled under as they appear.

Working the soil too often or when it is wet is not usually good for the organisms that live in the soil. Overworked soil can become pulverized and pack easily.

Baking the weeds by covering the weeds and soil with black plastic or a tarp also works on the principle of starving the plants. If the plants do not receive sunlight they cannot produce food and they slowly starve. In Alberta, plan to keep the plastic on a specific area for a year for the process to be effective. Do not be in a hurry to remove the plastic as weeds grow very early in the spring and until the ground freezes in the fall.

When herbicides first became available they were treated as the new way to garden. As people’s understanding of the chemicals increased use of herbicides become more restrictive with fewer varieties available to homeowners.

All herbicides, including organic ones, to go through standard testing before they are can be registered under the Pest Controls Product Act and sold. Each herbicide comes with instructions and restrictions. Problems occur when the instructions are not followed.

Knowing how the chemicals work helps the applicator apply the least amount of product to achieve the best results. Chemicals used to kill broadleaf plants in lawns work by accelerating the rate of a natural occurring chemical resulting is rapid growth that quickly kills the plant. This is seen in the twisted elongated shape of a sprayed dandelion. The chemicals work effectively when the plant is growing, nor dormant.

Round-up or all Glyphosates are nonselective which means there is a possibility of it killing any plant it touches. The herbicide works by destroying a plant enzyme that is needed in the production of food. Once destroyed the plant can no longer make the needed enzymes and the plant starves. Once again, the plant must be active for the chemical to be effective.

Horticultural Vinegar is also sold for weed control. Look for product that is registered under the Pest Controls Product Act.

The active ingredient in Horticultural vinegar is acetic acid at a concentration of 10% or more as opposed to the 5% acetic acid found grocery store vinegar.

Horticultural vinegar is often mixed with other ingredients and should be handled the same as other herbicides. Some brands of horticultural Vinegar are also licences to change the pH of soil or water. Like all pesticides, follow the manufacturer’s instructions and use proper precautions.

There are a number of ways to deal with unwanted plants. Each method has its good and bad points.

Linda Tomlinson is a horticulturalist that lives near Rocky Mountain House. She can be reached at

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