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What’s The Best Month To Apply Pre-Emergent?

Most pre-emergent articles on the internet focus on what “Month” of year is best for an application. That question is not inherently wrong, but like many things in life, the answer isn’t that simple. In this article, our goal is to provide you with the most accurate information about pre-emergent so that you can make the best decision for you. So find a comfortable chair, grab a cup of coffee (a small cup will do), and we trust that you’ll learn a lot. Enjoy!

The short answer for “What’s The Best Month to Apply Pre-emergent” is, “It depends.” Like you, I dislike when people give me that answer, however, please continue reading to learn what information you should be searching for before making your decision.

Let’s go way back, back to the beginning, on “What is pre-emergent?” Pre-emergent is a product that, when applied onto the ground, and gets into the soil, inhibits seeds from germinating (taking root). The fact is that as soon as weeds take root, they begin growing. As soon as they start growing, they grow bigger. And before you know it, your yard looks ugly.

Let’s Start A Program

To combat your ugly yard, we have a weed abatement program that tackles ungerminated seeds and germinated weeds. The reason we designed a weed abatement program is as follows. When we first began applying pre-emergent, we applied twice per year. For our first-time clients, setting foot on the property twice per year wasn’t enough to combat the weeds. This shouldn’t surprise most people because pre-emergent isn’t magical. Unfortunately we experienced a low retention rate with clients because they were unsatisfied.

Because we’re committed to providing clients a beautiful, clean yard, we implemented a six visits per year program. Our clients still received their regular two pre-emergent visits per year, but additionally they received four post-spray to tackle the growing weeds. These extra visits gave our clients the confidence to know that their yard was being taken care of. Here’s the breakdown of our program. Month 1 – pre and post spray. Months 3 & 5 – post spray only. Month 7 – pre and post spray. Months 9 & 11 – post spray only. As you can see, we’re now on the property every other month, and we’ve experienced a significant decrease in ungerminated seeds and germinated weeds, as well as a significant increase in client retention!

What Types of Weeds Does Pre-Emergent Control?

Without providing an exhaustive list, pre-emergent controls broadleaf seeds. Broadleaf is the term used to describe an extensive list of the most common weeds. Unless the weed(s) in your yard are extremely invasive and problematic, it’s fair to say that it will control the seeds associated with your broadleaf weeds.

How Is Pre-Emergent Applied?

The next question is, “How is pre-emergent applied?” Pre-emergent is applied in either liquid or solid (granular) form, with liquid being the most common in landscaping. Simply put, it’s more cost effective & easier to spray than use a granular spreader.

What Application Method Provides The Best Results?

The next question is, “What application method (liquid or granular) provides the best results?” In order to answer this question, you must understand one very important fact. Only, and I mean only, if the pre-emergent gets into the soil, as opposed to on top of the soil, will it successfully control seed germination. And the only way for it to get into the soil is if it’s a liquid that permeates into the soil. Follow me down this path.

No Rain No Good

If you spray liquid pre-emergent overtop the rocks, only a small portion of it will get through the rocks and into the soil, while most will stay stuck to the rocks. If you spread solid granular overtop the rocks, some of it will make it through the rocks and into the soil while some will get stuck on the rocks above the soil. But the granular that gets on top of the soil wouldn’t actually get into the soil because it’s a solid and not a liquid. At this point you might be thinking, “how in the world does the pre-emergent become liquid and get into the soil? I’m glad you asked that question and that’s what I’ll answer in the next paragraph.

Yes Rain Yes Good

In order to get pre-emergent into the soil, the ideal scenario would be for a rainstorm to come directly after it (liquid or granular) is applied. This would wash the liquid pre-emergent off the rocks and into the soil, or break down the granular pre-emergent into liquid (like salt dissolving) and wash it into the soil. Now that you understand the importance of it getting into the soil, let’s talk about rain.

Because we live in the high desert, where rain & snow are sparse, how does the pre-emergent actually get into the soil? I’m glad you’re still reading AND thinking, because this is where the rubber meets the road (or pre-emergent meets the soil). Since pre-emergent does not initially get into the soil, how does the sun & elements change the pre-emergent? There’s a very important term to your understanding and it’s called “residual.”


Residual is the amount of time a given element remains intact & active after being applied. For pre-emergent, the residual varies depending on the type & quantity used. The brand we use, paired with the rate we use, provides 8 months of residual. The brand of pre-emergent a majority of landscapers in Greater Prescott use, paired with the rate they use, provides 30 to 90 days of residual. These numbers are key to understanding how long pre-emergents “live” (so-to-speak) and how much time you have for it to get into the soil, where it will actually do what it’s designed to do.

30 to 90 Days or 8 Months?

Question: would you rather have 30 to 90 days or 8 months of residual? Most of us would pick 8 months because it extends the period of time the pre-emergent has to get into the soil and do what it’s designed to do. Think about this; how often does Greater Prescott go 30 to 90 days without rain or snow? If you’re tracking up to now, then you’re starting to understand why residual is vitally important to the success of your weed abatement program. In a rainy period, residual isn’t all that important because pre-emergent will likely get washed into the soil. On the other hand, in a dry period, residual is the difference between it remaining on top of the rocks versus getting into the soil.

Finally Back On Track

Understanding all the preceding information means that we can finally answer the original question you wanted answered; “What is the best month to apply pre-emergent?” Now that you’ve come this far, what’s your answer? If you guessed right before it rains, then we at Guardian Landscape would agree. Unfortunately, we at Guardian Landscape also know that rain & snow are unpredictable. Let’s nerd out on some historical rainfall data that will inform your decision. Greater Prescott averages 19 inches per year of moisture and here’s the monthly breakdown (in inches).

Based on this chart, on average July & August receive the most rain. But in 2020, July & August only received 2.08 inches versus 5.5 inches. Therefore, if your weed abatement program decision was based solely on the month of application, then your 2020 application may have experienced a lack of residual. The point we’re trying to drive into the soil is that because our moisture is erratic, make sure that your pre-emergent isn’t. We want our clients to have the beautiful, clean yards and that’s the reason that we have a weed abatement program and use a pre-emergent with an 8 month residual.

To finish, one question we often get is, “How much chemical will you use in my yard?” Now more than ever people desire to reduce the amount of chemicals they use. Because property sizes range drastically in Greater Prescott, below is a ballpark of how many ounces of our pre-emergent we use per acre:


Not only does our pre-emergent have greater residual, but we use 95% less chemicals!

To sum up this article, pre-emergent residual is arguably more important than what month it’s applied in, at least in Greater Prescott. Moreover, having an 8 month residual pre-emergent, paired with a 6 visits per year weed abatement program, gives us and our clients confidence that their yards will be beautiful. When you are talking to other landscape companies, make sure to ask about 1) their program and 2) the residual of the pre-emergent. And don’t forget we use 95% fewer chemicals than a majority of our clients! Thank you very much for taking the time to read this article. We trust that this knowledge soaked deep into the soil of your brain and now you have the information necessary to make the best decision for you.