Greetings; I would like to know if anyone has used the mexican black pebbles on top of the soil in a Lechuza sub-irrigation container? And if so, are there any draw backs in doing so, ie, would the rocks sufficate the plant? I would appreciate any comments. Thank you
Dawn

If you topdress thinly with the stones, there shouldn’t be a problem. The stones being "opaque" to water evaporation will mean that the top of the soil will not lose water as quickly as it would without a topdressing of stones, but the plant, if healthy, will transpire lots of water and the system will work just fine.

Don’t, however, lay down two or three inches of the stuff...just enough to cover.

Clem

Actually, there is more pore space between the pebbles than the soil particles, but it does mean that the evaporation point is happening a half inch or higher than it usually would. So, I am not contradicting Clem at all- several inches would affect the rate by adding so much extra volume. The most important water usage is happening at the level of the roots, anyway. Lechuza’s are a top-water sub-irrigation system, yes? The only concern I can think of is that eventually you will get some soluable salt build up on the rocks which is a little unsightly, but that is easily cleaned with some CLR.

Thanks Clem and Lynnae for your helpful response. The install was a success. I meant to ask, however, what your experience is in the use of plants that don’t require much water in sub-irrigation pots; such as mother-in-law tongues, dracaena’s, etc. Thank You

Dawn

Depends on the system.

CWI and its relatives are "intelligent" systems, and adaptable to different types of plants with different types of water usage patterns.

For example, if you have a Ficus in a very sunny atrium, you’d install the sensor tip close to the surface, so that it will release water into the rootball when the upper inch or two of the soil has dried down. For a plant that prefers "dry feet", inserting the sensor further down into the soil keeps the unit from refreshing until it has dried down that far.

Some might argue that subirrigation for plants that prefer relatively xeric conditions is overkill...others argue that the benefits of outfitting all plants in all situations is the key to consistently good maintenance results (due, in large part, to the technicians having only one "template" to master) and more than justifies the cost of outfitting every plant with subirrigation.

We find that dracaenas actually do better on a constant moisture regimen in many cases (except for very dark areas)...they may require a complete retrofit when initially potted into CWI, exchanging muck soils for a fast-draining soilless mix that works better in subirrigation systems, but they will repay you with great performance thereafter. Sansevierias are another matter, but if you would like to check out a subirrigated Sansevieria case study of sorts, go to:

http://www.insideplantslive.org/archives/cat_subirrigation.php

This shows a capmat-in-cachepot type of setup, or "poor man’s subirrigation" system, but it obviously works.

Bottom line: subirrigation management of varying types of tropical plants still requires some intelligent input on the part of the installer and maintenance staff. It’s not just a glorified "splash ’n’ dash" gimmick, but as a tool for increasing productivity and maximizing plant performance over the long term, you can’t beat it.

Clem