Invasive Roots in Garden beds

(Question)

Hi there,

I have moved into a new house last winter and was eager to get the garden going. I built five raised garden beds and filled them with quality triple mix. While some plants thrived, others – like all varieties of lettuce I planted, did very poorly – notably as time went on.

I had assumed this had to do with this year’s heat and drought and shrugged it off. However, when maintaining the beds I realized they got heavily knotted with invasive roots from underneath the soil.

I don’t know for sure, but suspect that a nearby silver maple is the culprit. I did some research and it appears to be the case.

Questions:
What is best way of preventing these roots from getting into the raised beds?

I have read arguments of trenching and building a barrier, as well as digging up beds and lining bottom and sides with landscape fabric. The latter appeals more to me.

Does lining raised beds (plenty deep) present any concerns? Will it be effective in keeping the roots out of my garden beds?

Appreciate your help.

(Answer)

Hi.

Using landscape cloth as a barrier to tree roots would likely be ineffective.  Consider that tree roots can penetrate the tiniest cracks in rock and eventually split the rock as the roots grow.  If they can do that, what use is landscape cloth?

Your best bet is going to be the trenching method as you mentioned earlier or you could install a metal barrier.  You can purchase metal roof flashing from hardware stores and put that a foot into the soil and about 4 inches above the soil line completely around your raised bed.  This should prevent any shallow-rooted trees from entering your raised bed.  The metal can be either inside or outside the bed

The ultimate method of keeping the roots out is of course to remove the source of the roots.  That would mean cutting down the tree and removing the stump to prevent the roots from growing.  This option is not always desirable since removal of a tree can be costly and create an unwanted hole in the landscape design.

Good Luck!