Apply an herbicide to the lawn during the spring to protect your lawn and garden from weeds. However, you should understand the different types of herbicides and how to best apply them to utilize their effectiveness.
Specific Versus Non-Specific Herbicides
Specific herbicides are designed to spot attack undesired plants and weeds and are most frequently recommended for home use. For example, if you have crabgrass growing in your lawn or along the sidewalk, you can apply a specific herbicide and kill only the crabgrass.
Non-specific herbicides are broad spectrum weed and plant killers that are used to clear all plants and vegetation where they are applied. They are frequently used by developers to clear builidng lots or by homeowners who are removing all plants from their yard or garden to prepare for new landscaping.
Pre-emergent herbicides are applied early in the growing season, before the ground has warmed and seeds begin to germinate. A pre-emergent herbicide prevents germination from occurring, thus stopping weed growth in its tracks. This type of herbicide creates a barrier around the seed that suffocates the seed.
You should either aerate your lawn before using a pre-emergent herbicide or avoid aeration all together. This is because aeration will essentially destroy the barrier seal that is created by the herbicide and will allow the weeds to germinate and grow, making the herbicide ineffective.
Once you have applied the pre-emergent herbicide, lightly water the lawn to activate the weed killer. Do not apply pre-emergent herbicides to newly planted or newly sodded lawns.
Once the growing season has begun and weeds have begun to appear, then it is time for you to apply a post-emergent herbicide to the lawn. Post-emergent herbicides go to the root source of the weed to kill it and can be very effective on dandelions and other types of common lawn weeds. However, they are not very effective on quack grass because of its deep root system.
Timing of Application
Early in the spring, before the temperature reaches 60 degrees, is the best time to apply a pre-emergent herbicide to the lawn to prevent new weeds from germinating and growing. As a rule-of-thumb, you should use pre-emergent herbicides when the weather is warm enough for you to only wear a light sweater.
Post-emergent herbicides should be used when temperature is higher than 60 degrees. The best time to apply them is when the temperature is between 60 and 90 degrees. You will need to apply this type of herbicide several times over the summer. Give your lawn a final application of post-emergent specific herbicides in the late fall to prevent growth of new weeds in the spring.
In addition to applying herbicides, help prevent weeds from growing by deep watering your lawn and leave the length of grass a little longer when you mow.