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landscape rocks absorb too much heat?

Posted by farmwife001 South Central PA (My Page) on
Mon, Jun 2, 08 at 14:07

I had to remove the mulch from my perrenials and replace it with river rock. I am wondering if the rocks won't become too hot or hold too much heat in hot weather and cause my plants to wither and/or die? Plants include day lillies, dianthus, coneflowers, golden marguerite and blanket flowers. Thanks for any comments or info. B

Follow-Up Postings:

RE: landscape rocks absorb too much heat?

I use river rock to mulch a five foot wide island planted with lavender and some fountain grass. The narrow island is surrounded by a concrete patio that I know reflects heat. We live in central Virginia where the summer sun is very strong and all the plants grow well using river rock as a mulch.

We also have river rock in another narrow island that we grow soft touch holly and small spirea in with success. All your plants are rather drought tolerant; I think they'll grow quite well. Happy gardening!

RE: landscape rocks absorb too much heat?

It depends on what your perennials are how well they grow in rock. Fountain grass and lavendar like hot and dry.
I hope you don't have plastic under the rock, as debris will collect and provide a medium for weeds and "critters" to grow and eventually you will have to remove the rock and clean the stuff out of there.
Your dianthus, marguerites and cone flower will not love the rock.
Curious, why did you "have" to remove the mulch?
Linda C

RE: landscape rocks absorb too much heat?

We put a pool in last fall and the pool guys recomended removing the mulch and use river rock.

RE: landscape rocks absorb too much heat?

  • Posted by nancyd 5/Rochester, NY (My Page) on
    Thu, Jun 5, 08 at 13:14

I personally prefer organic mulches for various reasons. Namely, weeding and raking is virtually impossible with stones. If you don't have many plants in the gravel, it might work. Not sure why the pool guys suggested using rock, but I have seen that look quite a bit around pools. I guess it's a personal preference. I copied a section of an article for you which identifies some pitfalls of gravel mulches if that's of any help:

Some homeowners use inorganic mulch materials such as gravel, pebbles, lava rock, or crushed rock. They may seem like a good choice as mulch since they will not decompose. They do not require annual replacement but pose some potential drawbacks. Be certain the material is compatible with the overall landscape design. They are well suited for a rock garden, herb garden, or Japanese design but may not be appropriate for a perennial flowerbed or a foundation planting.

In addition to the extra time it takes to apply these materials, some consideration should be given to problems associated with replanting shrubs or removal of these mulch materials. Light colored materials will reflect sunlight and cause the temperature around the plants to be warmer. Rock mulch absorbs heat during the day and releases the heat at night thus increasing water loss. Avoid using rock mulch around plants that might not grow well under these conditions.

A border of some type should be applied to keep the material in place; otherwise you may end-up with rocks in the lawn or on the driveway and sidewalk. When leaves and other debris fall into rock mulches, they are difficult to remove.

RE: landscape rocks absorb too much heat?

I have seen and swum in quite a few pools with organic mulch around them and as long as kids are encouraged not to walk in it and track it into the pool it works.
I also have seen one pool that had rock mulch...and I was there in early October when the nights were cooling down but the days still very warm....and the "critters" that lived in that rock and came out to bask in the sun would make your skin crawl! Maybe they live in the wood chips too....but I have never seen them to that extent!
I really best like the look of grass right up to the pool deck...but you have to use a catcher when you mow.
Linda C

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