Plant Growth Regulator (PGR)

Plant growth regulators (PGRs) are commonly used on Bermuda lawns to manage growth and reduce the frequency of mowing. Here’s a breakdown of their primary uses:

  1. Reduced Mowing Frequency: PGRs slow down the growth rate of the grass, which means you don’t have to mow as often. This is particularly useful during the growing season when Bermuda grass can require frequent cuts.
  2. Enhanced Color and Health: By inhibiting vertical growth, more of the plant’s resources are directed towards lateral growth and root development. This can lead to a denser, healthier lawn with improved color.
  3. Uniformity: PGRs promote more uniform grass growth, reducing the occurrence of patchy areas and contributing to a smooth, even lawn appearance.
  4. Weed Suppression: The thicker and healthier turf created by PGRs can help suppress weeds by limiting the space available for weed establishment and growth.

Does PGR help Bermuda grass spread?

Some plant growth regulators can result in shorter runners (stolons) in Bermuda grass. This effect arises because PGRs generally inhibit gibberellin, a plant hormone responsible for cell elongation. The reduction in gibberellin levels leads to shorter internodes—the segments between the joints of stolons—which can make the runners themselves shorter. The shorter runner length means that the grass might spread more slowly over large bare patches. This could be a drawback if rapid coverage is desired.

If you’re trying to get your grass to spread, there are other things you should be doing.

Not all types of PGR reduce lateral growth, some don’t have any affect to grass spreading, but none increase it’s ability to spread. A 2011 study compared 3 types of PGR to compare their affect on TifEagle.

PGR TypeLateral RegrowthClipping Weight ReductionTurf Quality (Rating)Root Length DensityBall Roll Distance Change
EthephonComparable to controlLeast effective (max 17%)Acceptable (6.8-7.1)UnaffectedNo effect
FlurprimidolImpeded (~25%)Most effective (>50%)Unacceptable (3.6-5.2)Reduced 25%Increased by 21 cm (AM), 26 cm (PM)
Trinexapac-ethylComparable to controlModerate reductionExcellent (8.0-8.4)Increased 33%Increased by 5 cm (AM), 10 cm (PM)
Source: https://ui.adsabs.harvard.edu/abs/2011AgrJ..103..988M/abstract

Best PGR Brand

Based on the above data, it’s clear trinexapac-ethyl is the best PGR based on these categories. TNex is a common trade name for the plant growth regulator trinexapac-ethyl. You can get a bottle for about $120 and split it with a friend so you’re only in for $60.

Buy T-Nex Plant Growth Regulator (Primo Maxx) 128oz

You can find some other brands in smaller quantities but the cost per ounce goes up dramatically.

How Often To Apply PGR?

Growing degree days (GDD) are a weather-based metric used to estimate the growth and development rates of plants. This measurement is particularly useful in agriculture, horticulture, and landscaping because it helps predict plant growth stages, optimal planting times, and pest management schedules.

We use GDD to calculate how often to apply PGR. Once you apply, use this calculator to count the GDD until you’ll apply again: https://www.greencastonline.com/growing-degree-days/home

Most people target 230-250 using a base temperature of 10 C. For example, in Arlington, Texas, in July and August, we average daily GDD of 22, which means PGD application would be every 10-11 days.

How Much PGR To Apply?

Application differs based on the type of Bermuda you have. If you have common Bermuda, you can apply more PGR. If you have hybrid, you’ll be using 3-4x less PGR per application. Follow the label to get the exact amount for your type of Bermuda grass.

Photo by Philippe DeLobbe: “T-Nex doing its thing! Been applying at 0.25 oz/k every 275 GDD mixed with 3 oz/k chelated iron.”

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