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Mr. Smarty Plants - Trimming of cordgrass plants

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Tuesday - November 20, 2007

From: Rockledge, FL
Region: Southeast
Topic: Grasses or Grass-like
Title: Trimming of cordgrass plants
Answered by: Barbara Medford and Joe Marcus

QUESTION:

We have planted more than 150 cordgrass plants (spartina bakeri) along the edges of the small pond at our condominium complex to try to prevent any further soil erosion between the buildings and the pond. The majority of each plant has turned brown with some green within them. They are anywhere from 2 1/2 to 3 feet tall and about the same in width. Our "pond doctor" says they should be cut back 6-12 inches from the tips. The person who sold them to us says "Don't touch them!" Two other credible (degreed) sources (different businesses)said to cut them back to 4 to 6 inches above the root base since it will allow for greater growth and a fuller plant next year. Lastly, the "authority" from the state says "Leave them alone because cutting them back will interfere with the photosynthesis process." The disagreement among these "educated sources" has created quite a dilemma in that we don't know whether they should be cut or left alone. The people of knowledge are so differing in their opinions that we don't know whom to believe. HELP!!!

ANSWER:

Spartina bakeri (Sand cordgrass) does not appear in our Native Plant Database; however, it is native to Florida and naturally grows in marsh and wetland areas. Refer to this Floridata website for more comprehensive information. If it has only grown to 3 feet tall, it has some growing yet to do, as it grows from 3 to 5 feet. It's a beautiful grass, and well chosen for the location you have described. Pruning or trimming it, on the other hand, is a fresh can of worms.

We can certainly understand those who do not wish to see it trimmed at all, because of its natural beauty. But, we agree that it could get out of hand; sand cordgrass has the potential to become invasive, as it is an aggressive, spreading plant. And, it's not going to be particularly fun to trim it-while it's blades are long and rough, like sandpaper, on the upper edges, it is not sharp. But wading into 150 cordgrass clumps with a pair of pruning shares is not an attractive prospect. At the Lady Bird Johnson Wildflower Center, as you may know, we grow a number of grasses (as well as many other plants) native to North America. There is no particular policy on trimming grasses here, but every couple of years or so we try to clean out the dead grass in a clump, partly for purely aesthetic reasons, as our gardens are display gardens, but also because the dead grass, in a drouth period, can become a fire danger. One suggestion was to trim every other plant several inches one year, and the others the next. And we don't feel they need to be trimmed down to little "meatballs" of 4 to 6 inches high. That's pretty labor intensive, and you're probably going to end up with some sort of compromise, depending on who is going to be doing the trimming, and what appears the most attractive.

Oh, and photosynthesis. Okay, there is some justification to worrying about that, if you were, say, going to mow the cordgrass down to lawn height. Photosynthesis is the conversion of light energy into chemical energy by living organisms. The raw materials are carbon dioxide and water, the energy source is sunlight, and the end products include glucose and oxygen. When plant experts are advising on pruning back a plant, they usually advise not pruning more than 1/3 to 1/2 of the upper structure, in order to leave the leaves (or blades, as it were) in sufficient numbers to manufacture food to sustain the plant. So, if you cut off a few inches or 1/3 of the height, you will leave plenty of material to photosynthesize. And cleaning out the dead and dry stuff makes more sunlight available to the plant to continue the process.

In the final analysis, we don't have a conclusive answer for you, either. We do recommend keeping the grasses cleaned up of dead material, we do think it contributes to the plant health to trim it some but not frequently, and we do urge that you be aware of both the invasive tendencies of the grass and the fire danger of dead and dry grasses.

 

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