Plant Growth Regulator for Lawns in Australia (Primo HG Guide)

Lawn exploding after rain? A plant growth regulator (PGR) slows vertical growth so you mow less, while encouraging sideways growth and roots for a thicker, tidier lawn. This long-form guide explains how PGRs work, when to use them in Australia, and how to apply them safely for consistent results.

What is a plant growth regulator for lawns?
A plant growth regulator (PGR) reduces vertical grass growth for 3–6 weeks so you mow less, while increasing lateral growth and root density for a denser, more uniform lawn.

Plant Growth Regulator for Lawns: What It Does

Most home-lawn PGRs use trinexapac-ethyl to temporarily slow vertical shoot growth. Instead of shooting skyward, grass invests in lateral growth (sideways tillering) and roots. Expect:

• Fewer mows during active growth
• Tighter canopy that masks thin patches and reduces scalping
• Richer colour and better uniformity across humps and hollows
• Stronger roots for heat/drought resilience
• Less weed pressure via a denser sward (note: not a herbicide)

How PGRs Work (plain English physiology)

Grasses grow upward in response to plant hormones called gibberellins. Trinexapac-ethyl temporarily inhibits a step in that pathway, so the plant doesn’t “stretch.” Energy is re-directed into tillering (more shoots), stolons/rhizomes (for couch/kikuyu), and rooting. That’s why lawns look neater for weeks and feel denser underfoot.

When to Use a PGR in Australia (QLD / NSW / VIC)

Apply only to actively growing turf. Skip during dormancy, renovation, or severe stress.

• QLD (SEQ & similar): September–May; strongest response spring → early autumn.
• NSW (coastal/metro): October–April; pause for cold snaps.
• VIC (metro/coastal): October–March; cool changes can slow uptake—time applications for mild, settled weather.

Weather watch: Apply on a dry day with no immediate rain/irrigation, and avoid heatwaves or waterlogged soil.

PGR Schedule by Mower Height (4–6 Week Rhythm)

Most home users re-apply every 4–6 weeks in the growing season.

• Lower cut / fast growth: closer to 4 weeks.
• Higher cut / steady growth: closer to 6 weeks.

If you extend too long, expect a rebound growth burst—resume the rhythm at the next suitable weather window.

Species Fit & Mowing Height Guidance

Common Australian home turfs respond well when used per label. Always confirm species on the product label.

• Couch/Bermuda: Excellent fit. Pairs well with lower cutting heights; improves density and uniformity.
• Buffalo: Good fit when cutting heights are moderate. Helps reduce scalping on uneven ground.
• Kikuyu: Very vigorous; PGRs help keep growth in check and reduce thatch pressure.
• Zoysia: Slow/steady grower; PGRs enhance uniformity and reduce seedhead appearance during surges.

Mowing tip: Keep blades sharp and avoid dropping height suddenly after application; sudden scalping wastes the benefit.

Where PGRs Fit in Your Lawn Program

PGRs don’t replace good basics—they amplify them:

• Watering: Deep, infrequent watering builds roots and complements PGR effects.
• Nutrition: Light, balanced feeding maintains colour; avoid heavy nitrogen that fights the growth-control goal.
• Renovation: Aeration and topdressing pair well outside dormancy; avoid PGRs immediately after heavy renovation until turf is stable.

Managing Rebound Growth

“Rebound” is a temporary growth surge when the PGR effect wears off after a longer interval or heavy rain/fertiliser push. Minimise it by:

• Sticking to your 4–6 week rhythm.
• Avoiding heavy nitrogen during the cycle.
• Mowing on schedule; don’t let clippings mat and shade the crown.

Compatibility with Other Products

Always check the label for mixing instructions. As general guidance:

• Non-ionic surfactant: Often improves leaf contact if permitted by label.
• Foliar iron: Good partner for colour without growth surge.
• Herbicides, fungicides, wetting agents: Only tank-mix when the label allows. If unsure, apply separately and observe intervals.

New for Home Lawns: Syngenta Primo HG (500 mL)

• Practical 500 mL pack for suburban lawns.
• Syngenta formulation reliability.
• Easy measuring for backpack/battery sprayers.
• Compatible with common species (confirm on label): couch/bermuda, buffalo, kikuyu, zoysia.

Buy Primo HG 500 mL

ALWAYS READ THE LABEL. Follow species, rates, PPE, and re-application timing exactly.

Primo HG vs Primo Maxx / Maxx II: Which One Should Homeowners Choose?

Quick answer: For typical suburban lawns, choose Primo HG (500 mL). Maxx/II are pro-size bottles for large programs.

Primo HG (Home)

• Active: Trinexapac-ethyl
• Pack size: 500 mL (home-friendly)
• Best for: Suburban lawns; easy measuring
• Sprayer: Backpack/battery sprayers
• Use case: Season-long control on a home lawn

Primo Maxx / Maxx II (Pro)

• Active: Trinexapac-ethyl
• Pack size: Larger professional bottles
• Best for: Large areas; cost-per-m² programs
• Sprayer: Pro rigs / larger tanks
• Use case: Frequent applications across multiple sites

Recommendation: Homeowners should buy Primo HG 500 mL. Browse pro options here: Primo Maxx / II Collection.

Safe Use: Kids, Pets, PPE & Re-Entry

• ALWAYS READ THE LABEL and follow APVMA-approved directions.
• Wear the listed PPE.
• Keep people and pets off until the spray is dry and any label re-entry period has passed.
• Be cautious on premium cultivars—patch test first.
• Avoid use on brand-new turf, during drought/heat stress, or winter dormancy.

Simple Application Walkthrough (How-To)

1. Measure area & calibrate sprayer (L per 100 m²). Accurate area is the foundation for correct dosing.
2. Mix to the Primo HG label. Use a measuring syringe/jug for small volumes; avoid guesswork.
3. If allowed on the label, add a non-ionic surfactant for even leaf coverage.
4. Spray evenly with steady pace and consistent overlap. A dye marker helps you see coverage.
5. Let it dry before irrigation, traffic, or mowing. Check label for any specific intervals.
6. Maintain your program: mow (usually less), water deeply, and use light feeding for colour.

Common Mistakes to Avoid

• Guessing rates or lawn size.
• Uneven spray pattern / missed strips; nozzles worn or wrong pressure.
• Applying to stressed or newly laid turf.
• Watering or mowing before the spray dries.
• Heavy nitrogen at the same time as PGR—pushes against the growth-control goal.

Pro Tips

• Pair with foliar iron for deeper green without surge growth.
• Use a spray dye marker to avoid overlaps and misses.
• Keep notes: date, weather, rate, result—helps dial in your interval.
• Edge cleanup: a quick trim keeps paths and garden borders looking sharp between mows.

Environmental & Practical Considerations

• Runoff: Avoid over-application and puddling; stop before drainage points.
• Weather: Skip extreme heat/cold and high winds for best uniformity and safety.
• Storage: Keep products in their original container, sealed, out of sun and away from kids/pets.
• Disposal: Follow label instructions and local regulations for containers and rinsate.

FAQs

How long does lawn PGR last?

Typically 3–6 weeks, with the less-mowing effect landing by week two.

Is trinexapac-ethyl safe for buffalo/kikuyu?

Yes when used per label. Always confirm species and rates on the product label and consider a patch test.

Will it kill weeds?

No. PGRs are not herbicides. They thicken turf to reduce new weed pressure; existing weeds need a separate plan.

Does PGR stop seedheads?

It reduces vertical surge and can improve uniformity, but seedheads are influenced by weather and species—results vary.

Ready to go?

• Add Primo HG 500 mL to cart

Need help with intervals by turf species and mower height? Message us with your turf type, lawn size, and cut height for a custom schedule.