The Plant Lady: Thinking about using raised beds? Here are a few tips you should know

There are many reasons to grow in raised beds versus in the ground — less than ideal soil, gophers, weeds and ergonomics are a few. Raised beds can vary drastically and it is important to do it right if you are going to go to the trouble and cost.

A variety of materials can be used to construct raised beds. They run the gamut from being quite fancy to simply a few large boulders lined up. Cinder blocks, rocks, bricks, corrugated metal and wood are the most common materials used. If you’re building with wood, use either cedar or redwood, as these hold up the best. Ensure the wood is not pressure-treated, as this is not advised for use in beds containing edibles.

How tall to build beds really depends on your ultimate goal and soil conditions. A slightly raised bed (4 to 8 inches) sometimes is all that is needed to improve garden productivity. For extreme rocky or tough soils, a taller raised bed is called for (12 to 18 inches). However, if your raised bed is going to be placed on cement or have a solid bottom, then you need to go at least 18 to 24 inches deep to accommodate for roots of tomatoes and larger plants. Too shallow of a bed will yield stunted roots, resulting in less-productive plants — not to mention more frequent water requirements.

Size depends on your space and needs. Keep in mind however most vegetables get pretty large. Tomatoes can get as big as 3 feet wide by 6 to 8 feet tall, so avoid making your beds too narrow. I suggest 2 feet as minimum width.

The key to a successful raised bed is the soil. When people experience problems with their garden even with a raised bed, it is most often because the soil is not up to par. I recommend using a potting soil instead of topsoil, or at least a 50/50 blend of topsoil/compost. Most bagged potting soils have a lot of redwood material and peat. While peat is good for holding moisture, it can be hard to re-wet. It can be a bit tricky when trying to decipher the labels on bags or blends. If purchasing in bulk from a rock yard, be sure to ask what is in their mixes. I try to get most people to either amend bagged potting soils with missing components or to purchase soil from a rock yard where you can literally put your hands in the soil and see what you are getting. The rock yard I buy my soil from now makes a similar blend that we had specially made for the UC Davis Botanical Conservatory.

The mix:

▪ 60% red lava (5/16” size) (Pumice can be substituted)

▪ 14% coarse sand

▪ 13% peat moss

▪ 13% redwood compost

When adding soil to your bed make sure to mix the native garden soil in with your new blend. You want to prevent as much soil line delineation as possible.

Soil volume will decrease after each season so it is important to backfill with more potting soil every few seasons.

Before each planting season (except if brand new soil), I blend in the following: compost and a thin layer of chicken manure or alfalfa pellets. This replenishes the nutrients that plants and watering utilize/leach.

If gophers are your nemesis, then adding hardwire cloth to the bottom of your bed is critical. This is the primary reason I have some raised beds. Hardwire should be stapled or nailed up along the sides of the beds a few inches instead of just being laid on the bottom of the raised bed.

Weeds may be another reason to do a garden in raised beds. While nothing is guaranteed to prevent weeds, raised beds can minimize the nuisance. Laying weed cloth on the bottom can slow weeds down, but I only recommend laying it when your beds are roughly 18 inches high. Weed cloth is root and water penetrable, but roots still need to work a bit to make it through. Keep in mind weeds such as bindweed and Bermuda grass will find their way in regardless, as will as weed seeds blowing in from surrounding areas.

This story was originally published March 2, 2020 at 1:40 PM.