Planting beneath trees

(Question)

I live in Brampton (clay soil) and have 3 huge 50ft blue spruce trees in my front yard. Until now, we have kept them with their bottom branches sweeping the ground. However, since it is thinning near the bottom, we are getting lots of weeds underneath. I have a complete thistle garden under one!
I spent a day pulling weeds under one, put down newspaper and a truckload of mulch and with a little maintenance it is looking better.
If we decide to trim up the bottom branches in the fall, what can I plant underneath that would crowd out the weeds and be low maintenance?
Thanks so much!
Jennifer Sansalone

(Answer)

Thank you for contacting the Toronto master gardeners with your inquiry.

Growing under trees, with competition for water, nutrients and light can create a lethal environment for many plant types. Any plant that sends a tap root down into the soil is likely to struggle, or may not even get past the thick matt of existing roots created by the trees.

Try planting species that spread by producing stolons or rhizomes. These plants run along the surface of the ground, with roots just under the surface- which pick up moisture and nutrients deposited by decomposing mulch on the soil surface.

Rhizomes are modified plant stems, which send out roots at intervals to secure the plant to the soil. Stolons, also called ‘runners,’ are a means of plant propagation.  The mother plant sends out runners, which anchor and bud- producing a new plant. The two plant types a fairly similar, although rhizomes can also travel vertically into the soil if conditions allow it.

Adding a shallow layer (about an inch thick) of organic compost over the area that you would like to cover with plants will ensure your new plants will have a supply of nutrients to reach out for. The compost will also trap valuable moisture. Check this compost layer each spring and top up as necessary.

Planting beneath trees is a question we’ve answered for other gardeners, so let me refer you to this detailed answer: Landscaping Plants Under a mature White Pine