Use of fir wood chips with needles as base in dirt veggie boxes
I have six or so cedar boxes 2' high that I will grow organic veggies in. In order to not need as much good soil, I want to fill part of the bottom of the boxes with fir wood chips that have needles mixed in. I have a pile of them on my property. Would the acid from the needles perk upward into the good soil? Also, what type of soil should I buy to fill the boxes? My soil is hard clay filled with shale and other rock. I could get a top soil w/o any fertilizer from Ace and add an organic mushroom compost or other organic compost. What do you suggest? Would I need more than 18" of good soil to accommodate any length of veggie roots? Thanks for your help. Patricia Collins Lebanon, OR
It's possible that the fir bark and needles could make the soil more acidic in the area touching the soil. Unlikely that the entire bed will become acidic since the water will flow down. Vegetables are pretty resilient and most would likely to be able to grow just fine in the 18" of soil. Some plants send down deeper root systems (like tomatoes). You might not notice a great effect on the plant's growth other than it might be a little smaller than it would have been if the roots hadn't been restricted.
Top soil amended with compost is a good choice. The compost will help improve the structure and drainage of the top soil. You will still need to fertilize your plants as compost can be low in needed nutrients. Many local nurseries and mulch/rock suppliers will deliver both top soil and compost in bulk or even as a pre-mix. If you purchase the soil and compost separately, add as layers to the bed and mix with a spade between layers.
For general vegetable gardening advice-including raised bed gardening-check out this publication: Growing Your Own. It's available as a free download.
Happy Gardening and thanks for using Ask An Expert!