The activity: Building and using raised beds.
Why: Raised bed gardening in Colorado can solve a lot of gardening challenges. By raising soil off the ground, it is easier to avoid compaction. The soil warms more quickly, and it might be easier to keep critters out of the garden. Raised beds, if properly designed, also can make gardening more accessible to people with physical limitations. And they might even be helpful in addressing soil problems.
How: Building a raised bed can be a fun project easily accomplished in a weekend. The bed may be a few inches off the ground or a few feet tall. The walls can be timbers, or boards, concrete reinforcing mesh or anything you use to construct a low wall. There are prefabricated kits that can be purchased from garden supply stores and catalogues.
If the site for your raised bed is on a slope, you can accommodate it by building the bed into the hill. In other words, the raised bed edge will be shorter on the high ground and taller on the low ground.
Once you've determined where you will build your bed, you must make a decision as to how to form an appropriate interface between the soil with which you build the bed up and the ground beneath. If your bed is less than 12 inches deep, you will want to cultivate the soil to a depth of about 8 inches and incorporate the soil being added to the raised bed. This can be done with either a roto tiller or a fork or shovel. That is important because even if you are adding soil or soil amendments, you want a graduated interface so water does not get trapped above or below the interface due to different soil types. This becomes less important if the bed is more than 12 inches deep as most plant root systems only grow down about 12 inches.
In general, raised beds should not be much wider than 4 feet. At that width, the garden can be accessed and maintained without having to step in it. Because you never step on the bed, soil compression doesn't become a issue.
If your garden is deep enough that you need to add soil to fill it, make sure that you purchase soil for outdoor use. This is available bagged at garden centers, or by the cubic yard at landscaping material yards. You don't want to use potting mixes.
A raised bed easily can be enclosed with deer netting or fencing to keep deer from munching your lettuce. If high enough, it might deter the dog from digging up the soil. If you have problems with rabbits, you might want to consider lining the walls with chicken wire.
Once your bed is constructed and filled, go ahead and plant it with flowers or vegetables. Crops should be rotated yearly to minimize plant disease problems. The garden should be fertilized according to the needs of your plants. If you're growing vegetables, shredded newspaper is good mulch because it will help control weeds and decompose quickly, adding organic matter to the soil. Use no more than an inch of mulch at a time.
A question frequently arises as to the safety of using preservative treated lumber for raised vegetable gardens. Prior to 2004, some wood for outdoor use was treated with a preservative containing arsenic. The replacement preservatives may pose a hazard because they contain copper. The jury is out as to whether the new preservatives are safe when they come into contact with edible plants. While there is a potential for contamination, most sources consider this a minimal risk. If you want to use this type of lumber, you can line it with heavy plastic to minimize leaching into the soil.
When: Construction can occur anytime the weather permits you to work outside. It's best to plant in the spring.
What's needed: Materials for the walls, basic tools (drill, hammer, tape measure, string level, etc), soil and plants or seeds. If using timbers, you will need reinforcing bar to anchor the timbers to the ground and each other.
When you have questions, call the Master Gardener Volunteer Help Desk at 520-7684 or email CSUmg2@el pasoco.com. Volunteers are available 9 a.m.-noon Monday through Friday.