The main problem with crabgrass is that it produces thousands of seeds that can remain dormant until the following season. To get rid of it, you have to remove existing plants before they have a chance to spread seeds and stop old seeds from germinating.

Weeds may grow back when pulled out if the root is not completely removed. Invasive weeds can regrow from just a small portion of remaining root, so using a weed-pulling tool can help ensure you remove the entire root. Weeds may grow back faster if roots aren’t fully removed, and incomplete removal could cause them to spread as well.

It’s not legal to intentionally damage a neighbor’s tree. Even if the roots of a tree encroach into your yard, if you damage or kill a tree that belongs to your neighbor, you can be held liable for the damage in most cases. Since herbicides can spread through the tree, causing damage to the whole tree and not just the roots that are on your side of the property line, you shouldn’t poison your neighbor’s tree. The other downside to this method is that if the tree dies, it can fall onto your property and cause more damage, so herbicides are best avoided in this circumstance.

The best time to fight crabgrass with pre-emergent herbicide is when forsythias tend to bloom. In the mid-Atlantic region, this is usually between April and May. Even if you're late to apply the herbicide, it’s effective as long as the crabgrass plant has fewer than five leaves.