How Plant Growth Regulation Can Make Your Lawn Thicker and Greener

In the world of professional lawn care, there are a lot of products out there you can use to improve your turf's overall health and appearance. Lawn care products like biostimulants and nitrogen-heavy lawn fertilizers contain additional microorganisms and nutrients to help achieve darker, greener grass.

But certain conditions can make your grass grow a little more quickly than you expect. Over-fertilization, over-watering, and mowing your lawn too short can cause speedy growth, which isn’t what you want. Before you start mowing in the spring, remember to wait till temperatures reach a consistent 50°F and your grass height is at least 2”-2.5” tall.

Fast growth means you have shallow-rooted grass, which is more vulnerable to weeds and pests. This is where plant growth regulators (PGRs) come in. Plant growth regulators are organic compounds you can add to grass to stop it from growing too quickly. If you’re not familiar with PGRs or you’d like to know more about the benefits of using them on your lawn — you’ve come to the right place. Just keep reading!

Related: How to Get a Green Lawn Fast — 3 Easy Tips

What Are Plant Growth Regulators?

Plant growth regulators actively influence your turf’s growth by allowing grass blades to flourish first. This is vital for promoting photosynthesis — the process by which your grass makes its food and becomes strong and healthy.

What Are the Main Benefits of Using PGRs?

Aside from promoting thick and healthy grass, plant growth regulators help cut down on lawn maintenance and ensure a deep green color. The big benefits of introducing PGRs are:

  1. They reduce how often you need to mow your lawn. Using plant growth regulators slows vertical growth, so instead of mowing twice a week (which is what we usually recommend), you’ll only need to mow once a week.
  2. They give you a healthier, better-looking lawn. Mowing your lawn less frequently means the grass blades have time to mature. Older grass blades are a dark green, whereas new grass blades are lighter in color.
  3. They give you more resilient grass. As your grass is healthier and stronger, it’s far more resilient to drought and disease.

Introducing plant growth regulation to your lawn-care regime is a good way to make sure your grass is at its best, both in appearance and health. 

When Should I Apply Plant Growth Regulator?

Generally, PGRs need to be applied every four to six weeks to control turf growth. Conduct your first application in early May and follow this up with monthly applications until September.

What’s the Best Plant Growth Regulator?

One of the best plant growth regulators on the market is Primo Maxx. It comes in a convenient 4 oz size, making it perfect to test out without breaking the bank. The active ingredient in Primo Maxx is a chemical called Trinexapac-ethyl. This interrupts the enzyme in your grass that promotes length. An added benefit of Primo Maxx is its potency. Small but mighty, one 4 oz container mixed with water is enough to treat 7,000-16,000 sq. ft depending on your grass type and application rate.

primo maxx bottle frontprimo max bottle


The measuring cup is built into this product, which makes application quick and easy. 

How Do I Apply Growth Regulators for Grass?

To apply Primo Maxx or your chosen plant growth stimulator, use this backpack sprayer. It’s sturdy, convenient, and supports higher pressures of application. For accuracy, use the foliar TeeJet tip (TeeJet XR11004VS), which produces very fine droplets to cover grass blades evenly. Primo Maxx doesn’t need to be watered in to work, so by using a fine spray tip, you’ll be maximizing plant growth regulator coverage and uptake. 

If you’re looking for a more cost-effective backpack sprayer option, this sprayer from Chapin is a great alternative.

With liquid applications, it can be hard to see where you’ve already put down the product. Using a turf mark indicator dye will help you avoid PGR overlaps, and you can use it to prevent over-applying liquid fungicides, fertilizers, and herbicides too.

TOP TIP: Prior to applying Primo Maxx or any liquid lawn-care products to your lawn, make sure you’re wearing the appropriate safety equipment — whatever the weather! Shoes with socks, long pants, a long sleeve shirt, and gloves are necessary to prevent any skin irritation. We also recommend wearing safety glasses to protect your eyes from stray droplets. 

How to Avoid Tip Burn from PGR

One of the main concerns some people have about using PGRs is “tip burn” — or a temporary bronzing of the lawn — after the first application. Visually, this can create a “burnt” look, with your blade tips looking like straw. 

To avoid this scenario, instead of applying Primo Maxx once a month, which will give you three to five weeks of grass growth regulation, try applying it every two weeks at half the monthly rate. For example, the monthly application rate for Primo Maxx on Kentucky Bluegrass is .60 oz. per 1000 square feet. With the split application method you would apply .30 oz on the 1st day of the month and another .30 oz on the 15th day of the month. This approach achieves all the benefits of PGRs (less mowing, more resilient grass, and a deep green color) without causing tip burn.

You can also incorporate your plant growth regulator application into your spoon-feeding program. Whenever you apply your first (liquid) fertilization at the beginning of the month, add Primo Maxx. You can also throw in some Primo Maxx when you’re doing a carbon kit or fertilizer application mid-month — if you’re applying liquid fertilizer anyway, you might as well save yourself some time and combine it with a PGR application. In fact, combining your plant growth regulator with a liquid fertilizer will also help prevent grass tip burn. 

TOP TIP: If you’re using nitrogen-heavy fertilizers, the use of PGRs is vital to prevent excessive growth. 

Split Application Rates for Primo Maxx

Here are the split application rates for Primo Maxx. They are half the monthly application rate and are what you would spray on the 1st and 15th of each month on 1000 square feet of turfgrass.

Cool Season Grass

Tall Fescue - .50 oz 
Kentucky Bluegrass - .30 oz 
Ryegrass - .50 oz 

Warm Season Grass

Bahiagrass - .50 oz
Common Bermudagrass - .38 oz
Hybrid Bermudagrass - .13 oz
Buffalograss - .50 oz
Centipedegrass -.25 oz
St. Augustinegrass - .05 oz
Zoysiagrass - .13 oz

Plant Growth Regulation: Final Thoughts

Evidence suggests that plant growth regulators don’t just maintain the health and color of your lawn, but they also promote resilience to environmental stress. Having healthy, strong, and flourishing grass is the best way to set yourself up for a successful growing season without paving the way for weed or pest invasions. If your grass is in good shape going into summer, you’ll save countless energy and time on other lawn products.

For a more detailed breakdown of how to nail every aspect of your lawn maintenance, our step-by-step guide can help you. Scroll to the bottom for a month-by-month breakdown to see where plant growth regulators will fit into your schedule.

Create the lawn of your dreams with a comprehensive course from the Golf Course Lawn Academy and enroll today.