Pre-emergent Weed Control: FAQs for Phoenix Residents

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If you’re constantly weeding your Phoenix or Anthem area yard, you may want to consider using a pre-emergent treatment to control the problem. These types of herbicides are applied to stop weed seeds from growing and act very differently from the weed killer sprays used after weeds have emerged.

We answer the most frequently asked questions about pre-emergent herbicide use below, including what it is, when it should be applied, if it harms your other plants, and more.

 What is pre-emergent weed control?

The answer is in the name – pre-emergent is applied BEFORE weeds appear. This type of liquid herbicide works to prevent weed seeds from growing.

How does pre-emergent herbicide work?

 Contrary to popular belief, pre-emergents don’t prevent seeds from germinating. Instead, they prevent a germinated seed from growing any further.

Once a seed has germinated, its root absorbs water from the surrounding soil. In areas that have been treated with pre-emergent herbicide, the water contains herbicide that stops the root (or the first set of leaves) from developing. As a result, the newly-germinated plant dies before it can emerge from the soil.

 When is pre-emergent applied?

The secret to pre-emergent effectiveness is the timing. Titan applies it in spring and fall, before the summer and winter rains common in the Phoenix and Anthem areas. The pre-emergent needs to be applied when soil temperature (not air temperature) reaches a level where seeds can take in water, but before the seeds germinate.

I had pre-emergent applied 6 months ago. Should I have it applied again?

Yes! Pre-emergent should be applied every 6 months, which is why Titan offers a weed management program that includes spring and fall pre-emergent, plus monthly spot spraying for any weeds that get through the pre-emergent barrier. Rain can fall during any month, which means that weeds can grow any month as well.

What are the benefits of pre-emergent?

Pre-emergent stops weeds from growing before they start, which can save you from a lot of weeding (or herbicide spraying) in your yard.

Will pre-emergent stop ALL weeds?

No, some weeds may get through the pre-emergent barrier, which is why we offer monthly spot treatments as well.

Will pre-emergent stop grass from growing in my yard?

It depends on the type of grass. Many warm-season grasses do not reproduce by seed, but instead by stolons and rhizomes.

Stolons grow from existing grasses. They’re above-ground stems that spread around the parent plant, where they grow a clone of the plant and send roots down into the soil. St. Augustine grass and Bermuda grass are common warm-season grasses in the Phoenix area that reproduce using stolons. Bermuda grass is often overseeded with ryegrass in winter.

Rhizomes, or rootstalks, also grow from existing grasses. They send out stalks underground horizontally. These new stalks grow roots and send a new shoot upwards through the soil. Bermuda grass also reproduces using rhizomes.

Because these types of grass don’t originate from seed, a pre-emergent will have no effect on them. However, it can stop cool-season ryegrass (which is grown from seed) from growing.

Will pre-emergent harm my trees, plants, or flowers?

Pre-emergent herbicides are not toxic in any way to existing plants, they just interrupt the process for seeds to mature. These herbicides also don’t penetrate far into the soil, usually staying in the top 1 to 2 inches (which is where weed seeds typically are). There are no negative effects to other plants in your yard.

Will it also stop flower or vegetable seeds from growing?

Because pre-emergent treatment prevents seeds from growing, it will also prevent many of the seeds you sow in treated areas from sprouting. Some plants, especially cool-season crops like broccoli, carrots, radishes, and peas can be planted after pre-emergent application. But for most flowering plants and other vegetables, it’s best to either wait a few months, apply the pre-emergent after seedlings have 5 or more true leaves, or transplant starts instead of growing from seed.

Is pre-emergent herbicide safe for children and pets?

Yes, but we recommend that you keep anyone from walking on the treated areas for the first 4 hours as it dries so they don’t track the chemicals into other areas. This will also let the mixture better penetrate the top layer of soil so it can be most effective.

Do I need to do anything after the application?

Titan recommends watering the pre-emergent into the soil and off any granite (such as the rocks and gravel found in most yards) within a day or two of treatment. This step is not necessary, but we have noticed that it helps with the effectiveness throughout the season.

What if it rains right after my pre-emergent application?

This helps the pre-emergent reach the soil (rather than the rocks or gravel), so this is helpful. If it rains, you can skip the watering mentioned above.

How is this different from spot weed killer?

Spot treatments are applied to weeds that have broken through the pre-emergent barrier. As the name implies, this treatment is concentrated on the weed itself and is not applied over a wide area like pre-emergent is.

Need Help With Weed Control?

Why not try a weed control program from Titan Pest Control/Titan Tree Care! Our weed control program prevents weeds before they appear through use of a pre-emergent applied twice a year. Once a month, a Titan technician also spot-treats any weeds that break through, leaving you with a beautifully weed-free yard.


Titan Tree Care is a full-service tree care company located in Anthem, AZ and serving all of North Phoenix. We offer a wide range of services to meet your tree care needs, including tree and palm trimming, tree pruning, tree removal, stump grinding, and more. We also offer insect or disease treatments and fertilization services. We are dedicated to providing high-quality, safe, and effective tree care services to our customers and work hard to ensure that your trees are healthy and look their best.