Mulch/Leaves potentially toxic to garden

Asked February 23, 2017, 7:36 PM EST

Recently we had an oak tree cut down, along with other small trees. They put the wood through a chipper and we have a lot of mulch. I am making a raised bed mound for raspberries, and am wondering if I can use this mulch? I have about a 6 inch below soil level trench that I am adding plant matter/compost and then will mound above soil level at least 6 inches. Additionally, I have a walnut tree - don't know type - Black/English? but have a lot of dead leaves that I was also hoping to add to the trench to break down. Any thoughts on damage potential to raspberries if I add this bark mulch/and/or leaves? I would like to add that the mulch has now been sitting 1 month and the leaves decomposing since last fall. Also, I intend to add nitrogen to the plot as I understand wood can bind it up. Any thoughts on what best to use for this?

Benton County Oregon mulch horticulture

1 Response

Very glad you sent this question to "Ask an Expert". There are a couple issues with your plan that would have a detrimental effect on successfully growing raspberries. Raspberries grow best is well drained soil, I am afraid that by planting them in a ‘trench’ you will be creating a basin that will not drain well. Raspberries are very susceptible to root rot and overly wet soil will add to the probability that your plant will develop it. The use of Oak or Walnut chips or leaves is not recommended. Both trees produce a chemical that is meant to protect the tree and will kill or damage your raspberries. Any wood chips worked into the soil will tend to ‘lock’ up the nitrogen in the soil as it decomposes. I recommend that you do not trench, but build your raised bed above the natural surface of the area you will plant in, ensuring that you will have adequate drainage. I am providing the link to a paper done by a World renowned Cane Fruit expert, B. Strik, PhD. This paper will provide excellent guidance for success with your raspberries. Good luck.