November 24, 2012

1 - When removing rock mulch from a landscape, be careful to avoid damaging tree and shrub roots.

Yard and Garden November 24, 2012


HELP! I'm in the process of clearing gravel and plastic from my yard...what work! When I get to the bare earth, should I till before putting down leaves, coffee grounds, and soil?

Terri T.

Via NMSU University Wide Extension


Removing gravel mulch is indeed a lot of work. There are several things to consider as you remove the rock mulch.

If there are desirable trees and shrubs within the landscape that was covered by gravel, important elements of their root system may be in danger of injury as you remove the gravel and when you rototill the soil. The important elements of the root systems are the very small roots that are responsible for absorbing water and nutrients. Larger roots are also important because they support the small, absorbing roots, and transmit water and nutrients from the smaller roots to the upper portion of the trees and shrubs. If there was plastic mulch under the rocks, especially if it was impermeable plastic, a large percentage of the absorbing roots will be at the soil surface or very near the surface. Just the removal of the protective covering from the roots may cause them to dry and die. Even if desirable trees and shrubs are some distance from the area from which rocks are removed, the sensitive roots can be found up to 4 or more times the height of the tree or shrub from the base of that plant. If there are irrigated plantings (flower beds, shrubs, lawns, etc.) in the area, the number of absorbing roots under the area of rocks may be minimal. If the landscape was predominantly rocks, then these roots are at risk. Injury to these plants, or even their death, is a possibility.

These roots are also a consideration when rototilling. The soil that had been covered by rocks will probably be very low in organic matter and compacted so that it does not readily accept water from irrigation or precipitation. Such soil will need to be managed to restore the organic matter as you mentioned regarding leaves, coffee, etc. If possible rototill before and after applying the organic matter. If the roots mentioned above are at risk from rototilling, minimize the rototilling and use a spading fork to loosen the soil either by turning the soil or by just pushing the tines of the form into the soil and pulling back on the handle of the fork to cause cracks to form in the soil (this will do less damage to the roots). If the roots are too dense, just apply the organic matter over the soil, keep it moist and let freezing and thawing and earthworms loosen the soil.

If there are not trees or shrubs nearby whose roots may be injured, then rototilling to incorporate the organic matter into the soil is a good practice. Moistening the soil, then rototilling the soil before applying the organic matter will allow you to more efficiently work the organic matter into the soil. If you are adding large quantities of organic matter, then you should add a 3 to 4 inch layer of organic material and then rototill before adding more material. If too much organic material is added at one time, it will not be evenly added to the soil.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email:, office: 505-865-7340, ext. 113.


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