If you have a shorter raised bed, you will need to do a little more math: length x width x height, but this time the height will be a fraction of 1 foot. For example, let’s say you have a bed that is 4 feet wide, 6 feet long, and 8 inches tall. First, multiply 4 feet x 6 feet to get 24 feet. Then divide 12 inches into 8 inches to get 0.667 (this is the fraction of 1 foot). Multiply 24 feet by 0.667 to get 16 cubic feet of soil. If your bed is 10 inches tall, use 0.834 for the height; if it is 6 inches tall, use 0.5 for the height.
Volume = 4 feet x 6 feet x (8 inches/12 inches) = 16 cubic feet (or 4 feet x 6 feet x 0.667 = 16 cubic feet)
Once you have figured out the cubic footage, multiply that total by 50 percent to find out how much compost you need. Then multiply the cubic footage total by 40 percent for how much coir, and then by 10 percent for perlite. For example:
Our bed needs 16 cubic feet of soil.
50 percent of 16 is 8 cubic feet of compost.
40 percent of 16 is 6.4 cubic feet of coir.
10 percent of 16 is 1.6 cubic feet of perlite.
Most bags of nursery potting soil and compost are sold in quantities of either 2 cubic feet or 1.5 cubic feet. Divide your totals for each material by the bag size you plan to buy, and that will tell you how many bags to load into your car.
Geeky Gardening TiP:
Old-School String Lines
When setting up mounded raised beds, place stakes at each corner of your target bed area and run string along the sides to map out clear lines for your beds. Whether you are building stacked mounds with layers of organic material, or just hilling up soil and compost, these lines will ensure that your beds are straight.
Berm Beds
Often called unconstructed beds or mounds, berm beds are the right choice for those who want to build a garden without actually building anything—not even stacks of organic matter. These beds also allow for more creativity. They can be formed into any shape, length, and size to accommodate your grand garden vision. Do you want a snaking berm with sunflowers along the pathway? A circle mound for your potato patch? Start digging.
There are several ways to build an unconstructed bed. A common practice is to mark out the bed areas (see the Old-School String Lines tip above) but instead of digging inside the bed area, dig soil out of the pathways and dump it onto the bed areas. This leaves the pathways lower than soil level and the beds higher than where they started. This technique was used by indigenous cultures to irrigate their crops and is often used in commercial agriculture today. The lower pathways fill with water, and the water is absorbed at the base of the mounds. Plant roots reach deeper for water, making them more resilient and drought tolerant. In permaculture, a variation of the pathway-turned-trench is called a swale and is often used to divert water away from flood-prone areas toward plant root zones (we’ll talk more about this in Chapter 7). Turn to Appendix D for other ways to build mounded beds, including “no-dig” beds.
Mounded raised beds are usually between 4 and 8 inches (10 and 20 cm) tall, though some adventurous gardeners have been known to build them waist-high. Pathway soil is mixed with compost to create loamy, well-drained soil that will hold together in mounds. The sides are sloped, and the surface of the mound either is flat across the top or has a gentle convex curve.
The theory behind this kind of mounded bed is that it creates more surface area. Sloped sides plus a flat top equals more soil exposed to the sun, which means that the soil thaws and warms more quickly in spring. Some gardeners take advantage of the extra surface area by planting crops on the slopes of each bed. You gain up to another foot of growing space if your beds are 6 inches (15 cm) tall. Be aware that slopes can erode during watering, so keep the slopes, if not the whole bed, well mulched to retain water and prevent soil loss.
In-Ground Planting
While unconstructed, or berm, beds are essentially the same as in-ground planting, the difference is height. An in-ground garden bed is made by loosening the existing soil of the desired planting area and working (digging) compost into the top 4 to 6 inches (10 to 15 cm). If you have existing soil that tends toward sand or loam, this is a fine choice. Those with clay soil will find it difficult to cultivate a garden this way without adding copious amounts of compost. In fact, clay soil is the reason raised beds were invented in the first place! Because clay soil doesn’t drain well and takes longer to thaw after winter, use this method only if you have sandy, well-draining soil.
Be sure to test your soil before planting in the area. Most university agriculture departments offer basic soil tests, and some will test your soil for heavy metals. Do you know the history of the land you plan to cultivate? With all of these good intentions for healthier living, it would be a shame to inadvertently poison yourself by growing food in soil contaminated with heavy metals, so be safe and get that soil tested. We’ll talk more about soil nutrients and heavy metals in Chapter 3.
Conditioning an in-ground planter takes about as much sweat and elbow grease as an unconstructed bed. Many first-time gardeners like to try this method before committing to a formalized garden layout. It doesn’t require a lot of planning, just a lot of compost. Work the compost down into the top 4 to 6 inches (10 to 15 cm) of soil. The deeper you loosen and amend the soil, the better your crops will grow. You can add decorative elements, like stone or brick borders, and put stepping stones throughout the planter to avoid compacting the soil.
No matter what type of raised bed you decide to use, just know that good planning pays off. Your garden will reward you with a bountiful harvest if you put some time and energy into the overall design and structure. Build your beds once and enjoy them for years to come.
Chapter 3
All about Soil
Soil is the foundation of every great garden. Without healthy soil, plants may grow, but they won’t thrive. Plants take up all of their nutrients from the soil (OK…plus the energy they get from the sun), and they need space to spread their roots, so it’s important to create and maintain a healthy soil environment for your crops. What makes up a healthy soil environment? A lot of things. Let’s take a look at the cast of characters.
Nutrients
Soil contains a vast array of elements and minerals that play an important role in a plant’s life. The “Big Three” are nitrogen (N), phosphorus (P), and potassium (K). Nitrogen is responsible for green, leafy growth. It’s what makes your tomato plants grow big, green, and bushy. Phosphorus helps those tomato plants develop strong roots and, more importantly, make flowers that eventually turn into fruits (yes, a tomato is technically a fruit). Potassium, sometimes referred to as potash, helps support a plant’s overall vigor as well as fruit development and disease resistance. Together, these three ingredients lend themselves to raising happy, productive vegetables.
Crops grow abundantly in healthy soil.
The Big Three do not work alone, however. They have a supporting cast, an ensemble of minor characters that help make their work easier. Trace minerals, including calcium, sulfur, iron, magnesium, manganese, and boron, all have jobs to do. They help facilitate
