Hi. New raised bed built this year. 8’by4′ about 8 to 10 hours of sun. filled with triple mix, manure and compost.
built to avoid maple roots. Built on older vegetable garden. Removed plants today and tried to dig, only to find maple roots, fine ones, back! What to do?
Thank you for contacting Toronto Master Gardeners.
It sounds like you have taken great care in building this new bed. The soil in the raised bed is probably significantly more nutritious than the surrounding yard soil.
Roots, not only of trees but shrubs and other plants, grow out and are attracted to areas with more water and nutrition. Your bed was a magnet for other plants this summer especially if you were watering it during this summer’s drought. Roots will search out the nutrients and water following paths with no resistance. They will not break through a barrier but if they find a crack or hole they will take advantage of it. Trying to fight the natural growth patterns can be difficult and in many cases futile. Working with the the habits of the roots you can trick them into going elsewhere. If there is a barrier the roots will change directions.
You do not mention if you lay down a barrier underneath your new raised bed before adding the new soil. There are different types of barriers you can use. Solid barriers that do not allow drainage are not recommended.
There are different types of landscape cloth that can be found at your local nursery which do not allow the the roots from other plants to enter the bed from underneath though they will probably still be attracted to the area. Alternatively you can use cardboard but you will need to ensure there are no cracks for the roots to find and grow through. No matter what you use over time it will breakdown and need replacing. One drawback to laying a barrier is worms will not be able to work their way up into the bed. You will need to replenish the soil regularly to maintain the soil at the current nutrient levels.
If you are growing vegetables or small plants the barrier at the bottom of the bed should not be an issue for you. If you decide to dig out the bed and lay down a barrier, be sure to use a tarp to dig the soil out onto. This will make refilling the bed significantly easier and you will not lose any of your soil volume. Try not to break down any clumps of soil as you dig the bed out and refill it. The clumping of the soil is an integral part of soil health and its ability to retain moisture and nutrients.
I am including a link below for further reading.
https://organicgardening.about.com/od/organicgardenmaintenance/a/raisedbedtips.htm