Build your beds somewhere that receives at least five to six hours of daily sunlight — the more, the better! Orient them north to south to prevent plants from shading each other out. Beds should be at least a foot wide, though no more than 4 feet across to make weeding and harvesting manageable. Six to 8 feet long is typical and cost-effective. Ten to 14 inches is an ideal height to accommodate strong roots. Leave at least 2 or 3 feet between beds for walking and wheelbarrow access.
The brilliance of a plank-and-rebar design (see above) is that each individual wall is easily replaced. Try naturally rot-resistant varieties of wood, such as oak, cedar, and redwood.
You want the kind that’s dark, rich, and loaded with microorganisms. Fill your beds with a mix of 50 to 60% good-quality topsoil and 40 to 50% well-aged compost. Before each new growing season, test your soil for pH and nutrient content. You can buy a kit at most home-improvement stores. If your test shows a need for additional nutrients like nitrogen and potassium, raise levels by working in amendments such as bone meal and kelp. Dress beds with an additional ½ inch of compost later in the growing season to increase organic matter and boost soil health.
If you’re building your beds in high summer, it’s not too late to plant fall crops. Sow seeds like carrots and lettuce directly into the soil, or buy midseason transplants for crops like kale and broccoli. If you’d rather wait until next year to plant, cover the soil in your new raised beds with a mixture of grass clippings and shredded leaves in autumn — the material will compost before you’re ready to start in spring.
Raised beds have fantastic drainage, which is great for plant health, but they dry out quickly. Give your plants a long drink in the early evening, but check them again on hot summer afternoons. If the soil is dry, it’s a real scorcher outside, or you live in a hot and arid climate, water again. A programmable drip-irrigation system (try a starter kit from dripworks.com) is inexpensive and convenient, delivering consistent moisture straight to plant roots. Invest in a timer component to save money and water.