I live in North York in the Clanton Park neighborhood, just north of Wilson Avenue and west of Bathurst Street. My property is covered with various plants and trees which have flourished over the years except in one area. The curved garden bed (see attached file) between my patio area and my neighbour’s chain link fence hasn’t provided for good plant growth. The area is shady but does receive dappled sun throughout the day and full sun starting at 5 PM. The issue however is not the shade. Even shade loving plants like coleus and hostas don’t do well in this area because of the fine mesh of roots and intermittent larger roots from my neighbour’s trees on their side of the fence.
Thankfully the largest of these trees was a hazard to fall and was just cut down which will relieve a lot of the issue, but there are still 3 young maples on the other side of the fence. Initially my thought was to place some barrels above ground and grow things in them but I’ve decided I’m not keen on that. What I want to do is dig out the entire bed to a depth necessary to ensure whatever I plant will have ample room for healthy root growth over time – I’m guessing 4 feet will be enough? I won’t be planting trees, just various perennials, hosts, and some annuals like coleus.
My idea is to create a barrier on the bottom and sides of the bed so that new tree roots don’t grow into the bed but allow for drainage at the bottom so my plants don’t rot. I guess I’d be effectively creating an underground flower pot with drainage.
I thought of laying down 2 by 4’s on the bottom, putting plywood or hard plastic sheet on top of the 2 by 4’ s, drilling drainage holes in the sheets, lining the sides of the bed with same bendable plastic sheets, then filling the bed with soil and planting. By putting the 2 by 4’s down first there would be an air pocket separating the bottom of the bed from the soil underneath so no tree roots could grow in, though maybe this would be important to do around the sides of the bed too. My general contractor recommends just lining the bottom with garden blanket or weed barrier material but I wonder if that would stop tree roots from poking through over time.
Any guidance on how dig to deep, what you’d recommend I use to create the barrier, or any other ideas/expertise would be much appreciated. Again, I’ve attached a pdf which includes a photo of the area as well as dimensions and a quick sketch of my idea.
Thank you for contacting Toronto Master Gardeners about your garden bed project. It is evident that you have put a lot of thought and planning into solving the growing problem in your garden. Concerning the use of landscape fabrics, the findings of various authors and personal experience indicates that landscape fabric is insufficient to prevent invasive root growth in the garden. Initially it works but in a relatively short period of time, perhaps 2 to 3 years and depending on the quality of the fabric, aggressive roots can overcome it. Your potential solution of boxing off the garden with wood will be unlikely, over time, to prevent root incursion into your garden. Roots will eventually find their way through drainage holes and wood structures and even toxic pressure treated wood is eventually subject to rot particularly when in constant contact with moist soil.
Before any digging on residential property, it is important and a requirement in Ontario, that homeowners call https://www.ontarioonecall.ca/homeowners/ to locate any gas and other lines that may be in the site of the proposed digging.
As for the roots of the removed tree, besides being labour intensive, their removal will deprive your plants of valuable nutrients, microrganisms and fungi. These enrich the established soil environment through the decomposition of the remaining roots. Rather than removing these roots, a thick organic mulch will help to suppress shoot growth. Removing any root shoots, over time, will exhaust the roots of this tree.
Concerning the roots of the young maple trees, a sturdy barrier would help decrease the likelihood of their root incursion. Since maples are somewhat shallow rooted, a depth of 4 feet is likely unnecessary. Munroe, in the second article down the page, suggests a depth of 30 cm for tree roots and lists a number of suitable materials and method of installation.
Finally, there is a concern about destabilizing the fence by digging a trench next to it. It is highly advisable, along with the requirement to “Call Before You Dig”, to consult with a member of Landscape Ontario, https://landscapeontario.com/concerning your project plans.
For more information, please see:
Munroe, S. (2020). How to install a root barrier. Retrieved Mar. 19, 2021 from https://homeguides.sfgate.com/stop-roots-raised-beds-88825.html
Wishing you the best with your garden creation project.