Invasive roots in raised beds

Asked April 9, 2018, 5:07 PM EDT

Over the last year, my two raised beds have developed these orange-red roots in them. They are not from any vegetable I've planted and slowly they are taking over the beds and strangling anything I try to plant. Any idea what they are and how I can rid my soil of them? I had a couple of years of good soil and then these things showed up. Thank you!

Multnomah County Oregon

1 Response

I strongly suspect that your raised bed is within the root zone of a tree or hedge. Frankly, it makes little difference which tree or shrub is the source because the roots will continue to invade the moist, fertile conditions in the bed. The majority of a tree’s “feeder roots” – those that absorb water and fertilizer elements – are generally within the top 12 to 18 inches of soil. Worse yet, those absorbing roots can extend to three times the width of the canopy or more, making it nearly impossible to escape tree roots in many a residential yard.

And, although roots don’t search for water, they proliferate abundantly when they encounter moist, fertile soil.

If you want the bed to remain where it is, you will probably need to dig out the roots yearly.

Some people line the beds with heavy plastic only to discover that the roots will find their way into the bed’s soil anyway.

Perhaps the most durable remedy I’ve heard of is to build a 12-inch deep raised bed on a concrete slab that juts out at least 4 inches on all sides. If you try this method, include occasional weep holes at the bed’s base to allow for drainage. Fill the bed with a 3- or 4-way planter mix and, then, mix in 2 inches of compost each year before you plant.

These publications may provide further insights. – “Raised bed Gardening” https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/fs270_1.pdf and “How to Build Your Own Raised-Bed Cloche” https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/ec1627.pdf.