Plant Growth Regulators 
Turf, Landscape and Garden

Introduction to Plant Growth Regulators

How Plant Growth Regulators Can Improve Plant Quality and Appearance, While Saving Time and Labor

Growth Regulators (PGRs) have been around for a long time and have been an important part of the professional turf and sports industry. Until recently they were not frequently used by homeowners. Their use is now on the rise as people discover the benefits of professional plant growth regulators. Growth regulators do not interfere with plant respiration, photosynthesis, or other internal functions.

There are growth regulators designed for many plant types, including grasses, trees and shrubs, and flowers. (There are even insecticides that are actually bio-friendly insect growth regulators.)

With plants, growth regulators are designed to stimulate a specific plant function or mimic a plant hormone that will help, hinder, or change the pattern of plant growth. There are now dozens of products that can perform an increasing array of functions.

If you are spraying it on shrubbery, the intent is to slow the growth so you do not have to trim it as often. The picture above shows the perfect example of where a PGR should be applied to reduce work hours. 

With turfgrass growth regulators, the original goal was to slow grass growth in order to reduce the amount clippings and frequency of mowing. Reducing labor costs was a powerful motivator for the use and development of PGRs.

They are now used along garden and cement edges to slow runner growth and reduce trimming time. They are used to improve grass appearance by preventing seedhead and stalk formations.

They are even used for preventing energy depletion that can be used during stress periods. Some that are labeled for grass are also labeled for other landscape plants as well. Uses include trees and shrubs, flowers and vegetables.

Timing is Important

To get the most from PGRs, they need to be timed and applied accurately. Some plant growth regulators, such as Bonzi and others, allow for creative uses for improved affect. Be sure to read and follow the label instructions carefully.

Popular Uses for Plant Growth Regulators Related to Turfgrass

  • For Slowing Grass Growth: Plant Growth Regulators sprayed on the lawn will slow the growth of labeled turf species by up to 50 percent for up to four weeks. This can be important for those who are seeking a reduction in clipping collection or mowing frequency.

    If you travel a lot, then applying a growth regulator may keep the howe owners association off your back. Plus, with over half of the states in the U.S. passing laws against disposing of yard wastes in landfills, PGRs are gaining attention.
  • Improved Grass Health and Stress Relief: Grass growth requires a substantial amount of energy, especially early in the season during the rapid growth phase of cool season varieties. As the grass enters the stresses of summer, energy reserves can be used up faster.

    Grass energy can be kept in reserve by slowing grass growth at least a month before the peak summer stress period begins. The energy stays in the roots instead of being used for growth, stalk and seed production. As a result, the grass will be able to handle stress and disease pressures better.
  • Reduced Trimming and Edging: A plant growth regulator sprayed round the base of trees, along sidewalks and driveway edges, along planter edges, etc., will slow grass and runner growth. This can be especially helpful for warm season grasses that spread by the production of stolons. Stolons are the above ground runners that readily challenge any boundary or border.

    Although they will not prevent the production of stolons, they can greatly slow them down. Some plant growth regulators are also labeled for ornamental trees and shrubs for maintaining their shape longer.
  • Annual Bluegrass (poa annua) Management: Annual bluegrass is a grassy weed that will green up before most all other grasses. It grows well in compacted sites and low cut grass, even golf greens. Annual bluegrass may be more of a concern for professional turf managers and golf course superintendents, where it is often a serious turf aesthetic and performance problem.

    However, more discriminating homeowners may find the control of annual bluegrass beneficial as well. Many of the same Plant growth regulators used for other landscape purposes can be use on annual bluegrass as well. They will prevent the production of seedheads in late fall and curtail the flush of growth in late winter and early spring. Over a period of time, with careful management, annual bluegrass will be greatly reduced or almost eliminated.
  • For Promoting the Growth of One Grass Species Over Another: As example is spraying annual ryegrass that has been overseeded into a bermudagrass lawn. The annual ryegrass should be sprayed a week or more before the bermudagrass is expected to emerge from dormancy.

    This slows the growth of the ryegrass and allows the bermudagrass to recover will less competition. Certain plant growth regulators have also been used to promote the growth of fescue where bermudagrass was taking over. This is accomplished by using a product that is labeled for bermudagrass, but has no affect on fescue. It may take a few seasons, but studies have shown to reduce the spread of bermuda by as much as 90 percent.

    In addition, overseeding the fescue each fall and mowing high will shade the bermudagrass considerably and help further weaken the plant. It is also used before plugging or seeding to reduce grass competition and allow extra time for seedlings and plugs to establish.
  • Reduce Mowing in Difficult Areas: Hillsides, right-of-ways, and difficult to mow areas could benefit from plant growth regulators. This is especially necessary with species where grass stalks and unsightly seed heads may be the primary reason for mowing.
  • Methods of Application and Important Tips

    Most turfgrass and other plant growth regulators are formulated for mixture with water and are foliarly absorbed through the leaf surface. Most products are labeled for use with a hand-held or backpack sprayer. Boom sprayers may also be permitted for larger areas. Always check the label for acceptable application methods. Other methods may be listed for licensed professionals. Make sure you have all proper clothing and protective equipment listed on the label before opening the container.

    Tips on Application

    Since plant growth regulators are foliarly absorbed, only the grass that is sprayed will be affected. Any grass that is missed will remain unaffected and will likely produce uneven grass growth. Spray on a calm day to avoid drift unto other plants.

    When spraying, walk in a straight line with the wand to the side. As you spray, try to catch the light glistening off the freshly sprayed grass. If you can see the glistening grass from only one direction, try walking backward on the return trip. You can also use a grass marking dye. These dyes are mixed directly into your spray solution and will indicate where you have sprayed and if you missed any areas.

    The “DO’s” of Using PGRs

  • Read the label carefully to make sure your grass type is listed. Not all weeds will be equally controlled. It may be best to control weedy grass, such as dallas grass, crabgrass or others, before using a PGR.
  • Only spray plant growth regulators on healthy grass. Spraying well ahead of seasonal disease pressure or environmental stress periods is okay and will help reserve energy to overcome problems. Damage occurring after the growth regulator is applied will take longer for the grass to recover.
  • For cool season grasses, the best times for use is in the spring and fall when the grass is growing. They shouldn’t be used indiscriminately, but rather, they should be planned carefully as to how you will gain the most from the product.

    For some, the least desirable time for PGRs on cool season grasses is in the summer. This is especially true for those who allow their grass to go dormant in hot weather. Uses may vary for those who provide optimum maintenance all season. How you use it will depend largely own how you maintain your grass.
  • Warm season grasses can be sprayed when they are actively growing. Heavier rates are usually required for edges where less trimming is desired. Check to make sure the product you want to use is labeled for your grass type.
  • The “DON’T’s” of Using PGRs

  • Plant growth regulators are not weed control herbicides and will not kill lawn weeds. They may have the same "slowing growth" effect on certain weeds as they do on grasses, but PGRs are not intended to control weeds. Some PGRs can be mixed together with weed control herbicides. Check the label to see if your herbicide is listed. Do not use a herbicide/PGR mixture on trees or plants other than grass.
  • Plant Growth Regulators should not be sprayed on grass that is already showing signs of disease, stress, or damage from insects or other injury. The slower growth will prevent the grass from quickly growing out or recovering from the damage.

    Where damage is visible, it may be best to delay using the product, while addressing the problem that is causing the damage. After the grass has recovered, then consider if it is a good time to apply a plant growth regulator. This applies to trees and shrubs as well.
  • Do not spray on windy days when the spray can be easily taken off target. This could affect other plants not intended to be sprayed.
  • There could be some grass discoloration with certain products, especially on bermudagrass. This usually occurs when using the heavier rates. The discoloration doesn’t harm the grass and usually lasts a short time. Consult the label for this information. If this is objectionable, avoid using the heavier rates on grasses that are prone to be discolored.
  • Many plant growth regulators should not be used where animals eat the grass directly after application. This includes dogs eating grass. Check the label if there is a delay between application and animal consumption of grass.
  • Ornamental Uses of Plant Growth Regulators

    Fruit Elimination: Fruit elimination is usually performed during the blossoming period. The tree must be sprayed during this period, before the fruit sets. Almost all trees that produce unwanted fruit can be treated. Read the label carefully to see if the product you plan to use lists your trees.

    Florel (Ethephon {(2-chloroethyl) phosphonic acid}is one of the more popular brands and will eliminate fruit on apple, carob, cottonwood, crabapple, elm, flowering pear, horse chestnut, maple, oak, olive, pine, sour orange, sweetgum, and sycamore. By eliminating the blosooms, the fruit will not develop.

    Sweetgum, however, has a more complicated flowering period and the timing must be more precise to control the “gumballs”. The window is much shorter. Consulting an arborist may be necessary for precise timing.

    Florel can also be used to accelerate tomato ripening. When timed correctly and sprayed on late season green tomatos, the fruit will ripen faster so it can be harvested before the first frost. Other fruit may be listed as well.

    There are also other fruit elimination products listed at the bottom of this page.

  • Reduction in growth of trees, shrubs, ground covers and ornamentals: Certain PGRs sprayed on trees, trimmed shrubs, and ornamental plants will slow the growth by reducing cell division at growing points. The plants keep their shape and size longer during the affected period.

    Growth may be most affected in plants with one main growth spurt each year when spray is timed correctly. Multiple applications may be allowed as stated on the label.
  • Do not spray trees and shrubs, etc. that have disease or other damage. The slowed growth will only delay the recovery.

  • Producing a fuller tree, without lateral growth: Dikegulac-Sodium active ingredient (i.e., Atrimmec) temporarily promotes lateral branch elongation within the plant. This will help fill gaps in shrubs and other bushes or trees where a full look is desired without promoting outward growth.

    More Rapid Tree Root Repair
  • Where root damage from home construction, etc. is suspected, the use of canopy growth regulators may help. The reduced canopy growth will force the tree or shrub to redirect the energy toward root growth. This has saved a lot of trees that may have been lost.

  • Elimination of Tree Root Suckers: Root suckers are up-right growing stems that grow along roots and at the base of stumps or trees. Left alone and they will grow to become a congested mess of literally hundreds of small shoots.

    Others can grow to become unwanted trees. “Sucker Stopper” (Naphthalene acetic acid) is a plant hormone product that promotes the demise of suckers by inhibiting the elongation and growth of tree sprouts.

    First trim the sprout with a lawn mower and spray the product on the sprouts. Sucker Stopper has many uses in the nursery and landscape industry as well. Depending on the amount of the active ingredient, certain Sucker Stopper products are labeled for Christmas tree farms to slow growth and help determine the shape of the tree. Others can be used around pruned limbs to control unsightly sprouts around the cut.
  • Building a Bigger Root System: When the roots of a tree are damaged, a PGR can be applied to slow canopy growth. With canopy grow slowed, the tree will redirect its energy to the roots to help rebuild and extend roots. This is extremely useful when roots are damaged by grading or other reasons.
  • Plant Growth Regulator Products for Turfgrass

    Product Uses, Active Ingredient (in bold print), and Product Trade Names. Products come and go, so these may not be available in future years. 

  • Reduces mowing frequency by growth reduction, build grasshealth and improve turf appearance.
    Mefluidide………………Embark T&O, Embark 2S, Stay-LO
  • Increases turf plant thickness and inhibits growth
    Paclobutrazol……………..TGR, Trimmit, Profile, Turf Enhancer
  • Reduces mowing frequency and enhances turf appearance.
  • Professional product: reduces mowing frequency, plant and stem elongation.
  • In my experience, Embark T&O is one of the safer plant growth regulators for home use. (Has been Discontinued) 

    Ornamental Plant Growth Regulator Products.

    Product Uses, Active Ingredient (in bold print), and Product Trade Names

  • Slows growth and reduces pruning.
    Mefluidide…………………Embark T&O, Embark 2S, Sta-LO
  • Inhibits flowering and inhibits fruiting. Removes mistletoe from coniferous and deciduous trees. Can be sprayed on late seaon tomatoes to hasten maturity.
  • For controlling the height and diameter of trees and shrubs. Promoting uniform flowering.
    Paclobutrazol………………..Bonzi, Trimmit
  • Growth retardant for shrubs, hedges, trees, and groundcover. Can be used on certain trees and shrubs to eliminate flowers and nuisance fruit.
  • These are only examples of PGR products and is not intented to be an exhaustive list. There are many other excellent products not listed. This is not intended to discriminate against any product. This list is not an endorsement of any product. Some products are for commercial use only and not available to homeowners. Read the label completely and carefully before using any turf or ornamental growth regulator. Some states or portions of states may not allow every stated use. Be sure to check to see if your intended use of a product is allowed where you live.

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