Peak in summer
PGR for Bermuda Grass: Primo Maxx Schedule, Rates, and GDD Timing
A plant growth regulator is the single biggest lever an enthusiast pulls: it makes Bermuda denser and darker while cutting mowing roughly in half. The catch is timing — run it on a fixed date and you get a rebound surge; run it on growing-degree-days and the regulation stays smooth. Here's how PGR works on Bermuda and how to keep the cadence automatic.
The system, step by step
- Step 1
Understand what PGR actually does
Primo Maxx (trinexapac-ethyl) is a Type II regulator: it blocks late-stage gibberellic-acid synthesis, the hormone that drives cell elongation and vertical growth. The plant's energy goes lateral instead — more tillers and stolons, denser turf, deeper color, stronger roots, and clipping yield commonly cut by around half. It's not a weed killer or a fertilizer; it changes how the plant spends what it already has, which is why it pairs with — never replaces — a sound feeding program.
- Step 2
Dial in the rate for your height of cut
Regulation is dose-dependent, so the rate is the whole game. Lower-cut Bermuda typically runs toward the lower end of the trinexapac-ethyl label range applied more often; taller lawns can go a bit higher, less often. Start conservative — it's far easier to add regulation than to wait out an over-application — spray in 1–2 gallons of water per 1,000 sq ft for even coverage, and add a surfactant and a marking dye so you don't double-hit a pass. Always mix to the label rate for your grass and height of cut.
Plant growth regulators are rate-sensitive — too much can discolor or stunt the lawn. Always read and follow the product label — it is the legal authority on rates, timing, and safety. These windows are regional estimates, not a prescription; defer to the label and your local extension office.
- Step 3
Reapply on GDD, not on a fixed date
Trinexapac-ethyl is metabolized faster in heat, so the reapplication window shifts with temperature, not the calendar. The widely used model reapplies at roughly 200 growing-degree-days (base 0°C / 32°F) — which lands near every 10–14 days in summer heat and stretches well past two weeks in cooler weather. Reapplying on GDD heads off the post-regulation 'rebound' surge — the burst of fast, leggy growth a calendar schedule lets through once the active ingredient runs out before your next spray.
- Step 4
Log every pass and watch the response
Note the date, rate, and GDD at each application, then watch how the lawn responds before the next one. The right cadence is the one your lawn shows you — logging is what turns it from guesswork into a repeatable program.
The system that runs it
How YardLedger handles it
Great lawns aren't luck — they're logged. YardLedger is the system behind the result: see how it all fits together.
- GDD-timed PGR reminders
- YardLedger tracks growing-degree-days from your local weather and reminds you when you're due to reapply (around 200 GDD, base 32°F) — so trinexapac-ethyl goes down on heat, not a fixed calendar, and you head off the rebound surge. (Available on paid plans.)
- PGR cadence log
- Log every pass with its date and rate — and the GDD at application — so your reapplication interval stays consistent and repeatable, and you can see what timing produced the best density and color.
- Product garage with rates & history
- Store your Primo Maxx rate per height of cut and keep the full application history, so every reapplication is consistent and you can see the regulation curve over the season.
Frequently asked questions
- How often should I apply Primo Maxx to Bermuda?
- In summer heat, roughly every 10–14 days — but the better answer is to reapply on growing-degree-days (about 200 GDD, base 0°C) rather than a fixed date, because the regulator breaks down faster when it's hot. GDD timing avoids the rebound growth surge that a calendar interval causes, and always follows the label.
- What does PGR do to a lawn?
- It suppresses vertical growth and redirects that energy into lateral density and color, so the lawn grows sideways, thickens, darkens, and needs mowing far less often. It's rate-sensitive, so apply to the label rate for your grass and height of cut.
- Will PGR hurt my lawn?
- Applied at the label rate it's safe and beneficial, but it's easy to over-apply — too much can bronze or stunt the turf, and the effects can't be undone once they're down. Start conservative, spray evenly with a marker dye, and let GDD timing keep you from stacking applications.