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Saturday - May 16, 2009

From: Colorado Springs, CO
Region: Rocky Mountain
Topic: Non-Natives, Compost and Mulch, Soils
Title: Is cement leaching into flower beds in Colorado Springs?
Answered by: Barbara Medford


I have posed this question to a number of garden centers in our area around Colorado Springs--only to rec. a repeated--"Gee, I don't know." When we moved to our new home there was a rock concrete wall terracing the front yard. I planted iris and day lilies at the base of the wall. They had thrived at our former home for a number of years and I am very fond of them. The wall was built by the former owners and not totally finished nor sealed on the top. The rock are cemented around a core of concrete blocks. The first summer both lilies and iris bloomed well. The past two summers they have become increasingly smaller in size, definitely fewer and smaller blooms. I have checked for grubs, bugs--feed bone meal. The bed has a soaker hose and mulch--yet they are not too wet or too dry. We purchased compost and dirt to finish terracing and landscaping. Iris and plants five feet away are thriving. Is is possible that the concrete is leaching into the soil and stunting the growth of the plants at the base? I realize that this is not a "native plant" question, but I am totally perplexed and frustrated. I have found your site to be highly interesting and very helpful as we have a large area of land north of the Springs we are attempting to return to a more natural landscape with grasses and wildflowers. Any thoughts would be greatly appreciated.


You are correct, cement leaching is way out of our field of expertise. The flowers you are referring to are not even natives of North America, and/or are so extensively hybridized that we would not be able to identify their ancestry. And you should remember that when you ask questions in a nursery, especially one not completely plant-related such as this one, that is not in their range of expertise, either.

We're going to offer you some alternative solutions, and perhaps you can work out what your problem is. Are they in sun or shade? We believe both the plants you are referring to are sun plants. Do they have heavy mulching over their roots, or rhizomes? Iris, in particular, can rot if their rhizomes are heavily covered-they need some air. 

Since you say some of the same plants a few feet away are doing fine, we would suggest you simply move the plants you are concerned with. That will give you time to try to solve the problem without sacrificing plants you wish to save. If they suffer from transplant shock, this is not going to help them, but likely won't kill them. Just trim off any foliage that is looking bad and replant in a more suitable place.

Now, to find out what the problem is with the wall. You need to know what is going on with the soil; perhaps in the process of building the wall, some toxic material got into the soil that is now making itself felt. You can get materials and instructions for getting a soil test by contacting the Colorado State University Extension Office, El Paso County. Dig down in there, see if you can find rubble or powdery material that looks like it doesn't belong.

And, finally, we Googled on "concrete leaching into soil" and got a number of references. One that we followed up briefly said concrete always leaches some lime. If this is the case, you can try neutralizing it with something that is naturally acidic, such as pine bark mulch or compost. We would suggest you continue to pursue that line of inquiry, starting with the concrete, and  follow up leads on the Internet.


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