Answer: If you're concerned about weeds growing up through the soil in your raised beds, I'd suggest laying down woven weed barrier cloth rather than plastic. The cloth will allow soil to drain - plastic will turn the planter into a tub and most plants do not like constantly wet feet. If you're planting flowering annuals and perennials, the soil needs to be only about 12-inches deep. If you're planting woody ornamentals, you'll need at least 18-inches and possibly 36-inches of depth. Bulbs will be happy with 8 to 10 inches of soil.
Q&A Library Searching Tips