Tuesday, September 27, 2011

Coping With Caliche!

People new to the desert may not be aware of a special type of soil we have here known as "caliche".  I have spent hours with a hose, jackhammer, and iron pick loosening up this subsurface clay for my plants.  It is not uncommon for Tucsonans to break their new shovel for one hole in the ground. The big question is, "Will this soil disappear?"  If you have an area that gets regular watering and you've removed most of the caliche, it will disappear and won't be an issue.  It's the dry or neglected areas that you are developing for a garden that make it difficult.  Usually, several days before I start digging, I'll throw a hose on the area to soften the ground.  I remember that this process took me an entire summer before establishing our fern garden!  One last personal point, as we start putting in our trees and shrubs for the October month, please please PLEASE be careful digging.  Have your house plan near you and know where your sewer, drip system and electrical wires are located before you start digging.  I only say this because I've watched many people start picking at what they think is caliche and it turns out to be cement protecting a sewer line. So before you start digging, look at your house plans:)  The following write is from one of my favorite people here in the desert, Cathy Cromell.  I've been reading her work and books for several years and she really touches upon a lot of the issues that we Tucsonans have in our own landscape.   
Illustration by Michael Gellatly.  The yellow zone is the hard and cement like "caliche".  Roots sometimes will reach an impasse at this point and spread out on top of this layer.  On the negative side, roots will not be "anchored" into the ground and during our wind events, the tree can be blown over.

"When digging becomes difficult, desert gardeners are quick to blame the Southwest’s notorious caliche. However, not all “hard labor” signifies you’ve struck this rock-hard substance. Sometimes that “thunk” sound is just your shovel striking extremely compacted desert soil—known as hardpan—that becomes even harder after heavy construction equipment compresses it.

You can distinguish the difference between caliche and hardpan by color: caliche is light (whitish-gray or cream), whereas hardpan usually is the same brownish color as the surrounding soil. Another method is to soak suspected areas with water. A layer of hardpan will soften with repeated soakings, allowing you to dig deeper a few inches at a time.

Wondering where that layer of caliche comes from? First, calcium combines with carbon dioxide dissolved in the soil’s water to form insoluble calcium carbonate. Over time, soil particles become cemented together by calcium carbonate to create solid deposits known as caliche. Your digging may unearth random chunks of caliche mixed in with soil and rocks or concrete-like layers of caliche several inches to several feet thick.

Caliche creates several problems for gardeners. First, roots cannot penetrate through it. Shallow root systems are susceptible to drought stress as well as uprooting during windstorms. In addition, plants must survive on the limited nutrients found in the soil above the caliche layer.

Second, water cannot soak through a tight caliche layer. This results in poorly drained, wet soil, which doesn’t provide the aeration that roots require. Think of a root ball in a planting hole set above caliche in the same way that a plant sits in a container without drainage holes. When water is unable to penetrate through the soil, salts cannot leach beyond the root zone. Over time, salt buildup kills plants.

Finally, calcium carbonate is a high pH substance; pH is a measure of acidity (low pH) and basicity (high pH). Although iron is available in the soil, high pH may inhibit a plant’s ability to absorb it, causing iron deficiency. This condition is more likely to impact non-native plants than natives.

- If soil is compacted, test the area’s drainage before planting. Dig a hole 1 foot deep. Fill with water twice during the day. If water remains 24 hours after the second filling, drainage is poor and should be dealt with before planting. Because caliche appears randomly in desert soils, the solution may be as easy as moving your planting site elsewhere.
- If there are no other site options, break apart and discard as much caliche as possible before planting. You may need to rent a jackhammer to crack through it. If it is impractical to remove a large and deep expanse of caliche, create narrow drainage holes—or “chimneys”—through the layer. Retest drainage after your efforts. When planting a tree, make a chimney hole on each side. To gain maximum benefit of water and air penetration for expanding roots, the chimneys should be about 5 feet out from the trunk.
- If breaking through caliche seems to be impossible, add a 2-foot layer of soil over the projected planting area and expanding outward to where roots eventually will grow. Use soil that is similar to the surrounding area. Soil must cover the entire circumference of the root zone based on the plant’s mature size, not its size when it is transplanted. Roots will expand one-and-a-half to four times beyond the mature canopy in their quest for water and nutrients, so this can be a significant and expensive amount of soil buildup. "  Written by Cathy Cromell
More tomorrow friends.....
Source: Caliche


  1. Very interesting! I had no idea what the ground was like there. Sounds like you get a good work out when planting things there.

  2. Oh it's quite the workout here!! The worst part is using a new shovel and breaking it while trying to dig the hole.

  3. You made a good point on testing the ground to see if it drains well. And oh I can't imagine people dug up cement thinking it was caliche... gosh... but really this is good info. Thanks!

  4. Man that sounds like some crazy stuff to deal with. We have some nasty clay stuff here but nothing like yours.


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