Master Gardener’s Scoop – May 16, 2018
By Jeanette M. Endres
“Oh my aching back!” is often heard when the first spring green weeds begin to emerge in the garden.
This is a great time to start to think of alternative ways to limit those plants that one might think of as not valued for use or beauty.
An alternative to weeding the garden is the raised or elevated bed.
Raised bed is the general term for any structure that has been “raised” approximately 10 to 30 inches from ground level.
Most beds referred to as elevated are approximately 30 inches high and allow the gardener to stand comfortably next to the bed.
Raised beds may not guarantee a weed free garden, but weeds and insects are easier to control since you can more easily control the composition of the soil. These beds often warm faster than a traditional garden as well.
The most obvious advantage to a raised bed is the comfort, especially with elevated beds, because they cause less wear and tear on the knees and back.
Some raised beds that are sold commercially are only one to two feet high and still require some stooping and kneeling to access. The bed should be no wider than 4 ½ to 5 feet across so there is no need to walk on the raised bed.
In addition to the height, another advantage to raising vegetables and flowers in a raised bed is that you have better control of the composition of soil.
Some sources suggest filling it with a blend of soilless mixtures that are superior to the native soil in your yard. The soil should be loose and rich with nutrients and organic matter.
Bags of raised bed mixtures can be purchased; however, another example using some top soil includes 60 % topsoil, 30% compost, 10% soilless growing mix containing peat, perilite, and/or vermiculite.
The amount of soil needed for the size of the raised bed can be calculated using various soil calculators found on line. For example, a 3 by 6 foot bed that is 10 inches deep will need 9 cubic feet of topsoil, 4.5 cubic feet of compost, and 1.5 cubic feet of soilless potting mix to provide the best environment for plant growth. It is still a good idea to have the soil tested.
Some other considerations are that the beds should be located in full sun with a water source nearby. Put at least quarter-inch drainage holes in the tubs. Remember that the elevated garden can still attract hungry visitors like deer, raccoon, birds, and squirrels.
Disadvantages of a raised or elevated bed include the expense of building the beds or the purchase of the raised bed from a catalog. Beds can cost hundreds of dollars depending on the size.
Generally, beds require more water and a good water supply is necessary. If the bed is less than 10 inches deep, the plants will dry out quickly. Using a drip watering system produces best results but adds cost.
I was fortunate to have a son-in-law that developed a design using long plastic tubs attached to a frame built from rot resistant wood. The total cost of materials was a little over $100 with the construction charged to my account as a “labor of love”.
We planted our elevated beds earlier this spring and our radish, lettuce, Swiss chard, cilantro, and carrots have all already sprouted.
Raised Bed Checklist
Step 1: Choose a location
The location for a raised bed should be in full sun for most fruits and vegetables.
• It should be near a water source for easy watering and should be close to the building for convenient harvesting.
• The bed can face any direction, but if you are building a longer bed, orienting the bed east and west will provide better light distribution.
Step 2: Kill off existing vegetation where your raised bed will go
• Grass and weeds can grow up through the new bed so it’s best to kill off any existing grass and weeds prior to putting the soil in the bed.
• This can be done naturally by placing plastic, cardboard, or layers of newspaper down over the vegetation. This will eliminate all light from the plants and will kill off the growth over a few months’ time. This can be done in the fall so that the area is ready for spring planting. Newspaper or cardboard can be left at the bottom of the bed as it will degrade, but plastic should be removed prior to placing soil in order to not impede the drainage of your bed.
• Another method is to spray the existing vegetation with a herbicide, like glyphosate, to kill all existing vegetation. Follow the safety and application instructions on the product label.
Step 3: Choose your construction materials
• Raised beds can be constructed out of just about anything. Some of the most popular choices include redwood or cedar wood, concrete blocks, bricks, stone, and various recycled materials.
• Redwood and cedar are some of the longest lasting woods for building raised beds.
• Some materials you want to avoid include some treated lumbers (read more about treated lumbers at http://pubs.cas.psu.edu/freepubs/pdfs/uc173.pdf), creosote treated railroad ties, and chemically treated pallet wood. Avoid any type of material that may be dangerous for food products to come in contact with. If these materials are used for bed construction, the bed may be lined with plastic to avoid contact of the materials with the soil.
• Choose whatever material will be the most economical and long lasting for your bed.
Step 4: Build your bed
• The size of the bed will depend on the number of people the bed will provide with food.
• Beds should be no more than 4 feet wide if accessible from both sides and 3 feet if accessible from one side. The length of the bed can be as long as needed.
• The depth of the bed should be at least 6 to 12 inches to promote good root growth.
• Beds built higher than 18 to 24 inches will need extra reinforcement.
• At least a 4-foot wide pathway between beds is standard for easy accessibility. This pathway can also be covered with mulch, straw, newspaper, etc., to prevent weeds. It can be planted with grass as long as the pathway is large enough to allow a mower to pass through.
Step 5: Fill your bed with soil
• The soil used for the bed should include good topsoil and lots of organic matter. This can be any combination of: purchased topsoil, compost, fine pine bark mulch, or peat moss.
• A soil mixture example could be: 60 percent topsoil, 30 percent compost, 10 percent soilless growing mix that contains peat moss, perlite, and/or vermiculite.
• Various websites have soil calculators available that can tell you how much soil is needed for a certain bed size.
• It’s recommended (though not required) to test the soil using a soil test kit prior to planting and in years following, to monitor pH and nutrient levels.
Step 6: Plant your bed
• Nearly anything can be grown in a raised bed. Cucurbit crops like melons and cucumbers may be better suited to a larger site though as they quickly fill a bed.
•Plant spacing is very important in a raised bed so that prime planting space is not wasted. Consult your seed packet for information on proper spacing. Information can also be found on U of I Extension websites (http://web.extension.illinois.edu/vegguide/step02.cfm) and in various books about ways to maximize planting space.
• Be sure to place taller vegetables on the appropriate side of the bed to prevent shading of other plants in the bed.
Visit the Illinois Vegetable Garden Guide website by U of I Extension for more information on raised beds and vegetable gardening: http://web.extension.illinois.edu/vegguide/
Source: Candice Miller, Extension Educator, Horticulture, [email protected]