Question
QUESTION: I have a very large spruce tree in my front yard. Since the grass around this tree is struggling to survive I am planning to lay down river rock on appr 3/4  of my front lawn. Do I have to remove the sod first or can I smother the grass with landscape fabric  topped with river rock.
As a note, none of the lower branches of the spruce have been cut, thus the rock would be placed around and not under the tree

ANSWER: Hello,

There is no need to remove the sod. The sod will retain the soil and prevent erosion. Use a fabric rated for weed control. A fabric rated only for erosion control may have a more porous weave spacing and that will allow more weeds to grow. Weed fabric is best used with mulch. An organic mulch placed under the rocks will eventually degrade and become ineffective,so perhaps you could lay down a layer of small sized gravel or sand over the fabric and then lay the rocks over the gravel. I would suggest at a 2 inch layer of sand or gravel or sand. Because of its smaller pore spaces,sand would be more effective than gravel.

Of course,as you have indicated,the rock should not be placed directly under the tree,as this would impede the tree roots from getting water and air and possibly cause a crush hazard to the roots if the rocks are very heavy. Good luck. Let me know if I can be of further help.

Mark  Harshman
http://www.harshmandrafting.com

---------- FOLLOW-UP ----------

QUESTION: Dear Mark
Thank you for this very informative reply. Rather than large river rock I was actually thinking of using the 1" - 2" size with only an occasional larger rock for decoration. Should I lay sand under this as well or would 2" of little rocks suffice?

Answer
Hello,

The smaller size rocks will have relatively less space between them than larger rocks and so less weeds will grow,but you will still get some weeds. I would not think that you would get alot of weeds with this design,but a sand layer under the rocks should eliminate 99 percent of weeds and the sand makes a nice foundation for the rocks. The rocks will be less likely to settle into the soil if resting on a layer of sand. Sand has very good compressive strength.

If there will be foot traffic on the area the sand will prevent the rocks from being forced into the soil below and will improve the feel of the surface under foot. If this surface will get a good bit of foot traffic,then you might want to consider removing the sod and preparing a base for the sand or gravel by compacting the soil below.

The sod will expand and contract with the freeze/thaw cycle,more or less,depending on how well water drains on it and this will effect your layer of sand and gravel. Sand and gravel are flexible materials and this will compensate somewhat for any expansion and contraction. The sod will also be less stable than a compacted base of soil only, since the sod is composed of mainly organic material. I would suggest you cut any grass on the surface to as low a height as possilbe and  compact the sod with a hand tamper,compaction machine or roller. Also, compact the sand and gravel in a similar manner. I am calling the 2 inch rocks you mentioned gravel here just for convenience.

Using sod as a base is not the best solution for a walking surface but for a lawn area that will receive only light foot traffic it will be adequate. The sod gives the advantage of holding the soil under the sand and gravel together and no mud will form under the sand and gravel and of course you will avoid the labor costs of removing the sod. As with all designs there are trade offs here. You have to decide what type of trade offs you want to make and what option you have more to gain from.

The smaller the size of the rocks,the less likely weeds will grow. Sand is just tiny rocks;the size of salt grains.

You also have to consider what thickness these materials will take. With a 2 inch layer of sand and then another 2 inches of gravel,thats a total of 4 inches. Will this surface even with the surrounding area. You will need some kind of edging to retain the material. The other option would be to remove the sod so that the material sits flush with the rest of the lawn or perhaps there are grade changes already existing that can be used. Good luck. Let me know if I can be of further help.

Mark Harshman
http://www.mahdrafting.com
Email: [email protected]

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