A raised bed is a bottomless frame set into a shallow trench. The sides can be made of almost any durable building material: rock, brick, concrete, and interlocking blocks. Retired watering troughs or claw foot bathtubs are the easiest raised beds, as long as they have the necessary capacity and drainage.
Mountain gardeners use raised beds to sidestep a long list of gardening challenges: Bad dirt is a non-issue, because you fill a raised bed with a customized soil-and-compost blend; drainage is built in and keeps erosion in check. Poor sun exposure isn’t a problem because beds can be positioned wherever light is more favorable. Plants can be spaced more closely together, so yields go up, water use efficiency is maximized, and weeds are crowded out of soil space. A really valuable asset is for gardeners who wage constant warfare against destructive burrowing animals; read on for specific building details that can keep raised bed gardens safe from these critters.
Location, Location, Location – Ideally, a north-to-south orientation takes full advantage of available sunlight. Avoid sites shaded by the house or under messy trees.
Planning & Building – At minimum build 3’ x 6’ beds. This size is wide enough to support sprawling tomatoes, but narrow enough to reach easily from both sides. The ideal height is 1 to 2 feet tall. Leave at least 18 inches between beds for walkways, or allow 2 ft if you want enough space to get through with a wheelbarrow or lawnmower. If possible, build more than one bed, which makes it easier to rotate crops and meet the watering needs of specific plants. Because the beds must be level, building on a flat spot avoids a lot of digging!
To prepare the site, get rid of turf and weeds. Then outline the bed dimensions on the ground with chalk-line, string, or a spare hose. Dig just deeply enough to bury about half of your first layer of building material. If there is no turf between your beds, put down some landscape fabric and cover it with pavers or a layer of gravel to improve drainage. Also, after running out in the rain for a fresh bell pepper, you and your mud-free shoes will appreciate these walkways!
In the bottom of the bed spread a layer of earth or gravel, then put down a layer of weed-suppressing landscape fabric extending it to the outer edge of the frame. Now is the time to think about pest control. The rich soil in a raised bed has worms and other delicacies that attract gophers; it also has young veggies that are irresistible to root-chomping voles. To keep out burrowing pests I recommend a bottom layer of hardware cloth, a 1” or less in diameter mesh grid of steel or galvanized metal.
Good Soil is Key – Do NOT fill the bed with native dirt. Instead, use a mix of peat moss, compost, soil-less potting soil, or growers’ mix. A good local potting soil retains moisture yet drains fast enough to allow deeper root growth. Blend “Tomato & Vegetable Food 4-4-6” and some gypsum into the top layers of the planting medium. For small beds use bagged potting soil designed specifically for our arid climate. Use a 2 x 4 to level the soil, and you are ready to plant. Put in lettuce, spinach, potatoes, horseradish, and/or onions at the first sign of a spring thaw, usually around the first few days of March.
Reduce Water Needs – “Aqua Boost Crystals” are made from a water-retentive polymer infused with seven different mycorrhizal fungi. The crystals absorb water and keep it at the plants’ roots while the mycorrhizal fungi animates soil to the point that plants root faster and deeper into the soil. If you have had trouble with watering issues in the past, try using these impressively effective crystals. All of my plants get a hearty dose of Aqua Boost as they are planted, especially those in raised beds and container gardens.
Until next week, I’ll see you at the garden center.
Ken Lain can be found throughout the week at Watters Garden Center, 1815 W. Iron Springs Rd in Prescott, or contacted through his web site at WattersGardenCenter.com or Facebook page www.Facebook.com/WattersGardenCenter .