Caliche in the Garden

Gardeners and landscapers in Texas and Arizona may be familiar with caliche. Commonly mined for use as a building and paving material, caliche is a sedimentary rock found in arid and semiarid environments. In Texas and Arizona, the caliche layer is often found just below the top soil, causing problems for gardeners.

Caliche layers in the soil involve soil that has been cemented into a hard sedimentary layer by calcium carbonate (lime). It appears as a white or cream-colored layer or lumps with layers ranging in thickness from just a few inches to several feet.

The problem for gardeners and landscapers is that the caliche layer often prevents roots from penetrating. This restricts root development and limits nutrient and water absorption for plants and trees. In addition, water can't move freely when tight caliche layers are present. This results in another problem for plants and trees: an accumulation of salt in top soil and lack of aeration. A third problem involves high pH and calcium carbonate levels in the soil which can lead to iron deficiency in plants.

Strategies for overcoming caliche in the garden including digging drainage holes, called chimney holes, through the caliche layer and removing the caliche and replacing it with soil in planting holes according to the following hole size guidelines:

  • Flower beds – one and a half feet deep by one and a half feet wide
  • Small shrubs – two feet deep by two feet wide
  • Large shrubs – three feet deep by three feet wide
  • Small trees – five feet deep by five feet wide
  • Large trees – six feet deep by six feet wide

If you plan on planting a lawn over soil with caliche present, make sure that you have a layer of top soil over the caliche that's at least eight inches thick.