pruning the big grass

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Large bunch grasses can be among the most challenging plants to prune. Every year they send up dozens of flowering stalks, which quickly turn into seed-heads shedding vast numbers of tiny potential grass sprouts all over the nearby landscape. Many gardeners resort to heavy weaponry to simply shear them right down to the ground, leaving behind an ugly, unhealthy, flat-topped “tuffet” of cut stems and leaves. Definitely not naturalistic!

I was recently faced with just such a challenge. Large clumps of perennial grass had gone to seed and grown out into unruly pompoms with long leaves (blades) trailing out across nearby plants. The client agreed that another annual shearing was not wanted, but could these grasses be limited back without sacrificing a natural look?

Of course they could! But it involved three different pruning methods, two of which were invented on the spot. Let’s start in the back garden, where a large grass looked like this in the “before” picture:

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First, the seed stems. They all had to come off. I reached in and clipped the seed stems way down among last year’s sheared-off stems. That worked to invisibly remove them, but there was a problem: I was also removing a lot of the green blades clinging to the stems. This was not good because those leaves made up about a third of the overall density. I was thinning too much!

I invented a new method just for this kind of grassy seed heads, clipping about half way up each stem, just a tiny bit above the node where the largest live blade was attached. Most of those blades were left in place, and the overall density was preserved. I call this new style of pruning “partial grass deadheading” because it leaves the lower half of the seed stalks in place while removing the business ends.

The second kind of pruning was also brand new. Unlike the leaves of broadleaf plants, grass blades elongate as they grow. This is an adaptation to herbivores that bite off the ends of the blades. Such shortened blades can still grow longer. But there are no grass-eating herbivores in most suburban gardens, and the blades of the bunch grasses tend to grow longer and longer. I realized that for these grasses to be trimmed in a healthy way I had to become that herbivore.

Having recently experienced a haircut, I realized that I could use a method similar to what my friend Janice had done to my head. I swept my hand across the ends of the over-long blades, scooping up a manageable handful and gently tugging outward. Then I clipped off the ends of all the blades in that handful, depositing the cut off bits into the debris bin. By repeating this operation all around the outer parts of the clump, I was able to reduce the lengths of the blades without creating a sheared off look. I call this pruning method “bunch grass haircut pruning.”

With the seed heads gone and the blades shortened all around, the bunch already looked much better. But the overall size of the bunch was too large and there were lots of old blades and stems around the base. It needed to be smaller without sacrificing the naturalistic look. I used a variant of undercut pruning. Reaching deep under at the base, I grabbed a small tuft and clipped it right at ground level, repeating and carefully observing the results all around the base of the plant. The density near the base was reduced, creating more of a fountain appearance and less of a pop-pom.

Here is the result on the bunch grass in the “before” picture above. Notice how much more visible are the small silvery plants near the base:

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Out in front of the house at the base of a tree, there are three more clumps of the same grass. Applying the same three pruning methods, these clumps were rapidly tamed. There is a “before” picture at the top of this post; here is another:

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Let’s have a closer look at the rightmost clump before pruning. See how dense are the seed stems, and how long the blades:

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This is how these grasses looked after the pruning. What do you think?

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I love pruning as much as I love creating deep nature gardens. I am available to prune almost anything in your garden (except mature trees, for which we bring in a licensed tree surgeon). If you are not near us, I am also available through online media (email or real-time video) to coach you on how to prune your plants.

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