Why Weeds Grow and How to Control Them

What is a weed?

A weed is defined as any plant growing in locations that are not desired, like in a lawn or landscape.

Why do weeds grow?

Weeds are considered opportunistic and grow when conditions are favorable, such as specific temperatures, lawn moisture levels, bare or thin turf areas, and can even grow in cracks in the roads, sidewalks or driveways.  Weeds have the ability to grow anywhere there’s room. Weed seeds come in abundance and from many sources while also having the ability to lay dormant in the soil for years before germinating. When actively growing, weeds produce thousands of seeds per plant and disperse them throughout the season. Some weeds like dandelions are spread with a little help from the wind. Other sources of weeds include poor quality grass seed purchased from the store and soils brought in for new plantings.

Types of weeds

There are three different types of weeds in every lawn and landscape bed. All can be controlled; however, some are easier than others.

1. Annual Weeds. These types of weeds spread by setting seed, germinating and growing for one season then dying off on their own at the end of their life cycle. These would include hairy bittercress, oxalis, groundsel and chickweed.
2. Biennial Weeds. Biennial weeds have a two-year life cycle. In the first year a seed germinates and produces a leafy plant. The following year, the plant flowers to produce seeds that then restart the new life cycle of the plant seed. These would include clover, wild carrot and prickly lettuce.
3. Perennial Weeds. These types of weeds grow for multiple seasons and spread by both setting seed and/or through their root system. These include dandelion, thistle and ground ivy.

How to kill weeds in the lawn

There are many ways to control or reduce weeds in a lawn. One option is to apply a preventative pre-emergent control; however, there is currently no single product that covers the entire spectrum of broadleaf weeds. Most commonly used are post-emergent herbicides when controlling weeds in a lawn or landscape.

Selective herbicides are another way to get rid of weeds in a lawn. The most widely used selective herbicides work by disrupting chemical processes happening inside the weeds. The herbicide mimics a natural plant chemical that stimulates uncontrollable growth. The weeds’ growth happens quicker than the plant can handle and dies.

Other selective herbicides target photosynthesis; the process in which plants produce energy/food from the sunlight it receives. By blocking the photosynthesis process, the weed basically starves to death.

There are also non-selective herbicides that target enzymes in the plant’s cells. The herbicide disrupts the sequence of chemical reactions and produces toxic compounds within the plant causing it to die off. A type of non-selective herbicide is the chemical called glyphosate, commonly known as “Round-Up.” A non-selective herbicide kills off any foliage that was sprayed. This type of product should be used with caution to reduce damaging desirable turf species and ornamental plants and grasses.

The natural way to get rid of weeds in your lawn is to hand pick them out. On smaller size lawns and mulch beds this is an effective way to control a small number of weeds. If you can pick the annual weeds before they flower and produce seed, you can aid in reducing the number of weeds that regrow. Keep in mind, weeds have roots that grow underground, hand pulling tears off the top foliage but the plant’s roots are left behind which can then regrow the plant. You need to remove all the roots to be successful and this is a difficult way to achieve it.

Cultural practices also play a key role in creating a more weed free lawn. Following these simple steps helps your lawn to be the healthiest it can be.

1. Keep your lawn dense. By having a thick, full lawn you essentially help “crowd out” the weeds. Weeds grow when there is space for them and a thick lawn reduces available space for the weeds to grow in. Any bare or thin areas at the end of the season should be seeded in the early fall (September) of each year to thicken up the turf density.
2. Fertilize regularly. Proper fertilization helps feed the lawn and keep it growing and healthy throughout the year.
3. Mow regularly and keep the grass blades high. It is recommended that the grass be kept at 3 – 3 ½ inches in length. Remove the top 1/3 of the grass blade at a time per mowing. This helps shade the soil underneath the grass canopy, which in turn helps reduce weed growth. Mow when the lawn needs to be mowed. Do not mow just because the lawn gets cut every Wednesday. Also, avoid scalping of the lawn by driveways, walkways, patios etc. with a weed wacker or trimmer. If the edges get cut too short they die off, causing the grass to thin back creating bare soil and an opportunity for the weeds to grow in that area.
4. Water properly. It is recommended a lawn with underground irrigation be watered 1- 1 ½ hours per zone twice per week. Hose-end sprinklers should be run for 4 hours per zone once per week both resulting in 1 inch of water on the lawn per week. Frequent and short watering causes a shallow root system that weakens the plants. Watering properly helps create a deeper, stronger root system in the lawn, which in turn creates a healthier lawn. To learn more about watering your lawn correctly, check out our watering blog.
5. Core aerate every year. Core Aeration is a great process that can be done; however, it is a costly process, which is why we recommend at least every other year. Core aeration helps improve the root system of the grass plant which creates a stronger plant overall. It also helps reduce the thatch layer and keep it at an optimal level which aids in better air circulation, water and nutrient infiltration to the root zone. For more benefits on core aeration, see our core aeration blog post.
6. Apply lime when the pH of the soil is low. Keeping the pH within the proper range (6.3 – 6.5) improves the availability of the nutrients in the soil making them more readily available to the grass plants. Here’s a great article on the benefits of applying lime to your lawn and having optimal pH levels.

Conclusion

Weeds are extremely opportunistic plants that can enter your lawn from a variety of different sources. The best way to reduce weeds is to have a healthy and dense lawn. That being said, not everyone has the perfect lawn and herbicides may be necessary to get rid of your weeds. Herbicides are a cost effective and not very labor-intensive way to keep your lawn and landscape weed free. If you are in our service area and have any questions about controlling weeds, please give our office a call.