Ultimate Guide to Raised Bed Gardening

Date:5/21/2018
Author:Terry Baldwin
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Growing a raised vegetable garden has many benefits—you know where your food came from, you can have all the fresh herbs, save so much money, you can garden in a small space, and you don't have to dig hard.

If you dream of plucking lush greens and juicy, fat tomatoes from your own raised bed, read on. Or if you've tried that and it didn't work out so well, don't give up! This guide is all you need to produce flourishing crops like a champ—from first plans to final harvest.

What's in this guide

  1. How to choose the best garden location
  2. What vegetables should you grow?
  3. Design & materials for raised garden beds
  4. Soil—what's best?
  5. Prepping and planting your raised bed
  6. Caring for your garden
  7. Dealing with garden pests & disease
  8. Harvesting your crops
  9. How can I find my local cooperative extension service?

How to choose the best garden location

6 hours of sunshine, minimum

The experts at the Michigan State University Extension say most vegetables and herbs need 6 hours of sunlight minimum, but 8 to 10 are better. Face your bed west or south, if possible.

View your potential site at all times of the day—a spot could be sunlit in the morning but shaded after lunch. Keep the season in mind, too. A site that's sunny in very early spring might not be after nearby trees leaf out. 

The closer to water, the better

Don't depend on rain to water your garden. Your vegetables will need regular watering, and you'll need to plan on doing that yourself. This chore will be easier if your garden is near an outdoor faucet or your house.

Decks and balconies need to handle extra weight

Will your garden be on a wood deck, balcony, or rooftop? If yes, be sure the structure can support the combined weight of the container(s), plants and wet soil. Wet dirt is heavy!

Don't plant around trees or shrubs

Thinking of building a raised garden around trees in your yard? The Nebraska Extension says nope: "When soil is piled over a root system, it immediately puts the lower roots out of range of their oxygen source. Roots begin to die, starting the tree on a long slow decline and, eventually, death."

What Vegetables Should You Grow?

If it can grow in the ground, it can grow in your raised bed. So grow what you like! Your kids can say no to Brussels sprouts and you can say fine, spinach it is. Your vegetable choices might be limited by plant spacing needs. Vegetables that grow underground, like carrots, can be planted closer together than bushy plants. Your garden may only have room for a single cucumber plant—vines can reach 8 feet long! Plant vining vegetables on vertical supports to increase your growing space.

Some vegetables are easier to grow than others, say Sandra Mason of the University of Illinois Extension and Kristine Hahn of the MSU Extension

Easy-to-grow veggies include most tomatoes, zucchini, radishes, leafy greens, leeks, onions, garlic, shallots, snow peas, snap peas, short carrots, beets, okra, turnips, sweet potatoes, and bush beans.

Harder to grow divas include broccoli, cauliflower, melons, celery, iceberg lettuce, peanuts, and artichokes.

Your region's climate also affects how easy or difficult some vegetables are to raise. Refer to your local county or university extension for specific information.

Buy disease-resistant plants when possible, advises Hahn. Check labels when shopping. "Disease-resistant varieties are denoted with a capital letter on the seed packet or in the seed catalog. For example, a VW means the tomato variety is resistant to verticillium wilt."

Need more help deciding what to grow? This well-produced resource from the Utah State University Extension has nutrition, planting and growing information on many fruits, vegetables and herbs (note that the planting dates are Utah-specific). Or check out this vegetable growing guide from the Cornell Cooperative Extension.

Plant flowers to attract the good bugs

Make sure your crops get pollinated. Mix flowers with your vegetables for bees and other pollinators. Pretty bouquets are a bonus.

Design and materials for raised garden beds

wood raised garden bed with ledge

A raised bed garden can simply be mounded earth, but experts at the Cornell Cooperative Extension, Chemung County, recommend framed beds to prevent soil erosion and maintain moisture levels.

Size

Fit the frame to your site. Most experts recommend 10- to 12-inch heights. Make sure you can reach the bed's center from both sides—then you won't have to step into the garden to tend it.

To garden while standing or sitting, use an elevated planter with legs or taller sides and a raised bottom. If your planter is very deep and you want to reduce the amount of soil you need to fill it, put empty plant pots or water bottles in the bottom.

Frames without bottoms are best for worm poop

With an open bottom, water can drain, roots can grow deeper, and our friends the earthworms can come and poop in the soil. Kentucky vegetable farmer Jesse Frost explains why worm poop (aka "castings") is so good for gardens: "Worm castings are loaded with tons of beneficial microorganisms but also many micro- and macro-nutrients that plants need to thrive. The castings improve soil structure and help the soil to more evenly distribute water. They protect from plant pathogens."

When do you need a bottom?

Your raised bed will need a bottom if you install it on a hard surface like concrete or wood, or if it's an elevated container, or being installed on top of toxic soil.

Toxic soil? Put a barrier on the bottom

Both lead and black walnut trees can poison your soil and your plants. Because plant roots can grow into the tainted ground, your raised garden should have landscape fabric or a solid bottom with drainage holes. Even a walnut tree in your neighbor's yard could cause problems. The juglone given off by black walnut trees is also in their roots and can reach plants outside the tree's drip line - extending "a distance about equal to the height of the tree," says the MSU Extension. Don't line the bottom with plastic—water won't be able to drain.

Drainage holes in container bottoms are needed to keep soil from getting waterlogged. The Sedgwick County Extension explains why drainage is so important: "Plant roots need oxygen as much as we do, and if the soil is full of water, there is no space for air! Water can smother the roots."

Contrary to popular belief, putting rocks in the bottom to improve drainage isn't a good idea. In her book Container Gardening Complete, Jessica Walliser says, "adding bulky materials to the bottom of the pot only serves to raise the water table inside the container, which floods the roots even more quickly."

Materials

Build your raised bed with wood, stone, bricks, concrete blocks, plastic tubs, metal stock tanks, retaining wall pavers, traction sand bags sold in tubes, even straw bales. Or save time and buy a kit. You can find kits made of wood, metal, and vinyl (like our white vinyl kit).

Metal

Metal frames and containers can look great. Just be prepared to water more often. Expert gardener Joe Lamp'l tells us "metal will absorb and reflect heat from the sun—more than other materials. As a result, your soil will tend to dry out more quickly, and foliage in the line of that reflective power might suffer." If you use metal, plan to water more often and put plants that like it hotter and drier in the spots that receive reflected heat.

Galvanized metal

horses drinking from metal stock tank

When steel is galvanized, it gets a protective zinc coating to prevent rust. Some gardeners worry that the zinc or cadmium (which can also be in galvanized metal) could get into the soil. I didn't find research confirming this. In a 1982 study, researchers grew lettuce and radishes in soil samples contaminated with zinc and cadmium and found no evidence of toxicity (Roger Jones, Trent University, Canada).

An expert at the United States Cooperative Extension points out that farm animals have drunk from galvanized stock tanks for years. And, if plants did absorb zinc or cadmium, "it will most likely be in very small amounts and the plants themselves will show toxicity if the amounts are too large." To be on the safe side, avoid using rusted galvanized containers.

Straw bales

straw bale

You can grow plants in straw bales (that haven't been sprayed with weed killer). The bales will break down after one season, but you can then use them for mulch or compost. 

Wood

raised garden with tomato cages

Wood is readily available at home stores and lumberyards. Use pressure-treated or "naturally decay-resistant wood such as eastern or western red cedar, northern white cedar, Osage orange, white oak, locust, or redwood," says Candice Hart, a horticulture educator with the University of Illinois Extension.

Can I use pressure-treated wood for a raised garden bed?

This question pops up frequently in gardening discussions. With its resistance to decay, pressure-treated wood seems like an ideal material for framing a garden, since it'll last longer than untreated wood. So what's the issue?

People are concerned the preservatives used to treat wood could end up in their vegetables. Here are a couple things to keep in mind. First, all these preservatives have undergone review by the EPA and have been approved for wood treatment. The most common preservative—MCA (micronized copper azole)—approved by the EPA for residential use contains copper particles and small amounts of another fungicide, an azole. According to Hart, plenty of research on the safety of treated wood in gardens has been done, "and the new treated lumbers have shown to be safe for garden use."

Second, most of the preservatives stay in the wood. Studies, such as this one, have shown that elements like copper don't travel from soil to wood to plant in any meaningful way. Furthermore, when trace elements like copper "are added to soil, most of what is added is not available for plant uptake." The elements are strongly bound to soil particles, especially clay and organic matter, according to the Penn State University Extension.

However, if you still have doubts, line the sides of the bed with polyethylene plastic.

Creosote-treated railroad ties aren't advised for gardens. Creosote is an industrial wood preservative that the EPA has “not approved to treat wood for residential use, including landscaping timbers or garden borders."

Tires

Old tires probably aren't good plant containers. "As tires wear, they give off minute, dust-like rubber particles containing cadmium that easily disperse and accumulate in soils and on plants," point out Donald R. Hodel and Andrew C. Chang, University of California Cooperative Extension.

Recycled materials: Proceed with caution

Be wary of reusing salvaged materials to build a raised bed. Materials including concrete, bricks, lumber, and rocks could be toxic if they were "salvaged from a structure that may have been located on a contaminated site (such as a gas station, industrial site, etc.) or...from an older building that may have been painted with lead paint or insulated with asbestos at one time," warn John W. Vick and Joshua Poe in a University of Louisville container gardening guide.

Vertical supports

squash plants growing on trellis

Plants that climb or have heavy fruit need supports like stakes, cages or a trellis so they don't flop all over the place. Staking also improves air movement through the garden. Make sure your supports are tall and sturdy enough to support mature vegetables or fruit.

Here are some plant support suggestions from Rebecca Krans, Michigan State University Extension:

  • Tomatoes—1-2 main stems per 5-6 ft. stake
  • Pole beans—6-7 ft. supports
  • Clinging veggies (peas, cucumbers)—5-6 ft. high chicken wire
  • Heavy melons and winter squash—strong structures and slings to support heavy fruits

Soil—what's best?

Say no to plain ol' dirt, say yes to soil mixes

While your bed's design is important, what goes in it matters more. Filling your raised bed with earth straight from the ground will cause problems. The Cornell Cooperative Extension, Chemung County, explains that ordinary garden dirt (aka topsoil) tends "to crust over, settle, and shrink away from the frames" and also be compacted by heavy rainfall, especially if it contains a lot of clay. 

A better way is to mix in organic matter, like compost, well-rotted manure or peat moss. This improves drainage, adding nutrients at the same time. The University of Illinois Extension advises using “at least 1/3 existing soil in the soil mixture."

Here's a soil mix from Cornell:

  • 1 part organic matter (peat moss, compost)
  • 1 part sand or perlite (for drainage)
  • 2 parts soil

Compost is awesome, except when it kills your plants

If you don't make your own compost, you can find it at garden centers and other facilities. Know that some compost can contain herbicides that don't easily break down. This "killer compost" can stunt and ruin your herbs and vegetables. Persistent herbicides can be present in compost made from farm manure, golf-course grass clippings, even your own lawn, if you've applied weed killer. Bottom line? Know where your compost came from!

Bagged soils

When buying commercial mixes, look for those containing a blend of organic material. Avoid bags of top soil. The Illinois Extension points out that some products labeled top soil “tend to be largely sedge peat. While they are inexpensive and look very good, once put into a pot they are poorly drained and poorly aerated." However, you can mix this peat with other soilless products or compost.

Container gardening? Avoid these potting soils

Container-grown plants are pickier about their dirt. Jessica Walliser advises gardeners to stay away from these types of potting soils:

  • Very heavy bags. The mix is likely "too dense for good container performance."
  • Mixes that contain soil. They "may contain weed seeds or plant pathogens."
  • Stinky mixes.
  • Bags "that contain sprouting seeds, moss, or mold."

How many bags do you need?

Soil mixes are usually sold in 3-cubic-foot bags. The University of Illinois offers this formula for figuring out how many bags to get:

Multiply length x width x height of your raised bed (in feet, not inches). Then divide by 3.
For example: 4 ft. x 8 ft. x 1 ft. = 32. You'll need 32 cubic feet of soil, which means about 11 bags of soil.

Prepping and planting your raised bed

Preparation

If grass or weeds are growing on the spot you've planned for your raised garden, they've got to go before you add soil. Sorry, but simply burying them in dirt won't cut it—they can return and haunt your veggies. But removing sod and weeds is a lot of work! I recommend the lazy gardener no-dig method.

It's easy, and it works. At least a month before spring (fall is ideal), place cardboard or several sheets of newspaper over the vegetation, top with compost, then add your soil mix. The grass dies and breaks down, fertilizing the soil. In spring, set up your bed and start planting!

Planting: seeds or transplants?

seedlings in paper pots
Photo by Christian Joudrey on Unsplash

Seed catalogs give you so many choices, while garden centers have vegetables already growing. Which should you plant? The answer is both. Some vegetables take longer to mature, and you'll have better results if they get a head start as transplants. Here are some recs from the University of Illinois Extension:

Best planted as seeds: Leafy vegetables, beets, peas, greens, carrots, radish, snap beans, sweet corn, squash, turnips, and cucumbers.

Transplant these: tomatoes, peppers, eggplant, broccoli, cauliflower, cabbage, onion (sets), rhubarb, asparagus, sweet potatoes and herbs.

When to plant your raised garden

Some vegetables can be planted in early spring, while the weather is still cool. Others need to wait until after the threat of frost has passed. This helpful spring garden calculator from expert gardener and writer Margaret Roach tells you when to plant seeds and transplants outdoors. Your local extension can tell you your area's final frost date.

Take your soil’s temperature before planting, Kim Pokorny of the Oregon State University advises. The temperature affects how well seeds and transplants will grow. Some seeds refuse to germinate in cold soil—they'll just lie there and rot, like that leftover sushi you forgot in your car.

Extreme soil temperatures can destroy fine roots on young plants. Fresh transplants can be killed by "hot or cold surface soils," according to master gardener and associate professor Dr. Linda Chalker-Scott in the Journal of Environmental Horticulture. You can find soil thermometers at garden centers in a wide price range.

Pokorny lists soil temps recommended for planting these seeds:

Cool soil, down to 40 degrees: arugula, fava beans, kale, lettuce, pak choi, parsnips, peas, radicchio, radishes and spinach seed 
Above 50 degrees: Chinese cabbage, leeks, onions, Swiss chard, turnips 
60 degrees: beans, beets, broccoli, Brussels sprouts, cabbage, carrots, cauliflower 
Above 70 degrees: tomatoes, eggplants, peppers, cucumbers, squash, corn, melons

Get a head start on the growing season

raised garden beds with row covers

With a raised bed, you can cheat the weather and give your garden a head start. Soil in a raised bed typically warms up faster than ground soil. You can speed the process even more by laying sheets of plastic on the bed for a week or more. After planting cold-sensitive plants, cover them with "a cloche, fabric or cold frame," says Pokorny.

A cold frame is "a shallow, unheated box with a transparent cover," Beth Berlin, an educator with the University of Minnesota Extension, explains. Plants in a cold frame can bask in the sun's heat and still be protected from cold.

You can build a cold frame right over your bed. Learn how with this guide: How to Build Your Own Raised-Bed Cloche (cold frame) by Sam D. Angima and Bill Biernacki of Oregon State University.

Transplanting tips

Allow a week to harden off plants. Greenhouse-grown plants need to be acclimated to wind and direct sun. Toughen up those babies by gradually leaving them outside for longer and longer periods.

Don't transplant during the hottest part of the day. Being transplanted is stressful enough. Your veggies will be adapt faster if you plant them on a cloudy day, in early morning, or late afternoon. You can also shade new transplants with a light cloth.

Free the roots. Gently loosen roots if they’re circling the soil ball. If roots are matted on the bottom, break them apart.

Nip the buds. Removing flowers lets the plant put all its energy into growing roots, which is "essential with transplanting," according to the MSU Extension. This will result in more flowering and a better harvest.

Protect from frost. Can't it just stay warm for a minute? If frost is predicted, cover your seedlings.

Garden layout

planting a raised garden bed

Keep tall vegetables and trellises from shading shorter plants by locating them on the northern end of your bed, Cornell recommends. Position tall plants "just south of the trellis."

When spacing plants, follow seed and plant labels. With a raised garden bed, you don't need to make room for a path, so you can space rows closer together. But no cramming! Air needs to circulate around plants. This helps prevent diseases and fungal spores from developing.

Caring for your garden

Mulch your plants

cabbage plants in mulched garden
Photo by Arnaldo Aldana on Unsplash

After your plants have settled in, mulch them to help conserve water, maintain soil temperature, reduce weeds, and keep dirt from washing away or compacting in heavy rains.

The best type of mulch for a vegetable garden is loose, fast-decomposing material such as grass clippings (without herbicides), chopped leaves, compost, or straw (without seeds), according to Linda Chalker-Scott.

Add mulch gradually, building from 1 to 3 inches over a few weeks. Spread mulch in a large area around vining vegetables like cucumbers to keep the maturing fruit from touching soil, which can cause rot, the Missouri Botanical Garden says.

Feeding

If your garden bed has rich soil, you might not need fertilizer. "Feed the soil to feed your plants," says MSU's Rebecca Krans. Focus on keeping soil healthy by top-dressing with compost throughout the season. A soil test can tell you if you need to fertilize your garden.

Watering

vegetable garden being watered
Photo by Marcus Spiske on Unsplash

Because soil in a raised bed gets warmer than the ground, it can dry out faster. During hot spells, your bed may need daily watering.

Watering tips (from the Cornell Cooperative Extension of Suffolk County):

  • Deep, infrequent watering is best for healthy plants.
  • Avoid overhead watering—it can encourage fungal diseases.
  • Concentrate on watering at the root zone.
  • Soaker hoses and drip irrigation "can reduce watering needs by up to half."
  • Water in the morning if you can—it's cooler and "evaporation is lower."
  • Recycle water from cooking and washing vegetables.

Soaker hoses & drip irrigation

For ultimate convenience, use soaker hoses (easy) or a drip irrigation system (more complex) with a timer. A soaker hose is laid on top of the soil around plant rows and connected to a regular hose. A drip irrigation system has more components. Both systems conserve water use and apply water directly to plant roots, where it's needed.

Capture rainwater with a rain barrel

Save money and conserve water by capturing rainwater with a rain barrel. Terry Gibb, Michigan State University Extension, explains: "A rain barrel is a large container with a top that a home’s downspout fits into and a spigot at the bottom to get the water out for use...[rainwater] contains no chlorine, lime or calcium which makes it beneficial for gardens." If you want to install a rain barrel, here are instructions from the Rutgers Agricultural Experiment Station.

Keep beds clean

Remove detritus, weed seedlings, and diseased or dead plant matter. If a walnut tree's nearby, be sure to remove any fallen walnut leaves, hulls and seedlings.

Dealing with garden pests & disease

Critter control

chipmunk on raised garden
Photo by Tony Fortunato on Unsplash

Friendly forest animals are happy to help Snow White, but don’t let that fool you. They get hungry and will meet up at your garden for brunch. So you have to take steps to stop them.

The lazy way to protect your plants from critters is to use lightweight plastic netting. The netting comes in rolls and is usually black or dark green—practically invisible from even a small distance. You can cut it with scissors. Just toss it over plants in the early evening and remove it in the morning—it only takes a minute. And it's reusable for years. This effectively stopped deer from stripping my hydrangeas and day lilies.

Are the neighborhood deer too bold and hangry? Here's another solution, from Beth Jarvis and David Bavero of the University of Minnesota Extension. Because deer avoid "small, penned-in sites," they suggest enclosing your raised bed with a 4-foot-high fence or a snow fence.

Deer repellents: They're meant to repel deer via a terrible taste or smell. But effectiveness is iffy. Jarvis and Bavero reported that a Connecticut study testing 6 repellents found that effectiveness ranged from 15% to 46%.

Tunneling rodents: Some critters, like gophers, will sneak underneath your garden to eat root vegetables. Block them by placing hardware cloth on the bottom of your raised bed.

Mothballs: nope. Some gardeners use mothballs to control squirrels and other rodents. Margaret Roach warns against this. Mothballs are a pesticide. "The label of any pesticide, including mothballs, specifies exactly where and how you can legally use the product. Using mothballs in a way not specified by the label is not only illegal, but can harm people, pets or the environment," Roach says.

Insect control

bee on lavender
Photo by Aaron Burden on Unsplash

Some insects will attack your plants, others will attack the attackers or pollinate your plants, and knowing who’s who is hard. This infographic lists some of the good guys.

Remember this about pesticides: They will destroy all the bugs—even the good ones. And what about birds that eat the poisoned bugs?

To be on the safe side, don't put pesticides on your plants. I find knocking the bad guys into a cup of soapy water very effective. But if you're absent minded, don't drop them into your coffee cup, speaking from experience.

If slugs are a problem, kill them kindly by setting shallow dishes of stale beer outside your raised bed. They love it and don't mind if the hop-malt balance is off.

An effective non-toxic way to control adult insects is placing a floating row cover over your garden in spring right after planting. Just "be sure to remove the cover when flowers appear as bees and other pollinators will need to get to the flowers to pollinate," says Rebecca Krans.

If bugs are blitzing your crops and you need more ammunition, use low-impact pesticides such as insecticidal soaps, horticultural oils and biopesticides.

To identify bugs, check out this excellent pest identification guide from the West Virginia University Extension.

Plant diseases

Disease is an ongoing concern. Plants can catch diseases via soil, wind, water or insects, according to Jessica Walliser. Symptoms include spots, discolored or powdery patches, and wilting.

To help prevent disease, follow Walliser's tips:

  • Plant disease-resistant varieties
  • Allow space for air to circulate
  • Water in the morning, and water at the roots
  • Remove and destroy infected leaves
  • Clean your garden tools
  • Don't over-fertilize

For help figuring out what's wrong with your plants, check out the University of Minnesota Extension’s diagnostic  guide.

Harvesting your crops

red tomatoes with stems
Photo by Andrea Riezzo on Unsplash

Pick vegetables as soon as they mature. The more you pick, the more plants will produce. Morning is the best time to harvest, "ideally before 10:00 a.m., when the weather is still cool and water content within the plants is still high," says Jessica Walliser. And refrigerate your haul right away.

Handle veggies carefully while harvesting—nicks and bruises will spoil them faster. Most produce should be stored in cold (32-40 degrees F.), moist environments. Perforated plastic bags are better than unperforated bags, which develop condensation that leads to mold, says the University of Minnesota.

Need recipe ideas for enjoying your harvest? let me recommend my favorite vegetable-centered cookbook, "The Love and Lemons Cookbook" by Jeanine Donofrio and Jack Mathews.

Harvesting herbs

Walliser recommends regularly harvesting herbs "to encourage more growth and to keep them from going to flower." Snip the flowers off herbs that you grow for the leaves, such as basil and oregano. Once the flowers set seed, the plant will think it’s done.

Preserving your harvest

Your garden will be so prolific, you'll have more produce than you and your friends can eat in a week. Preserve the extra by freezing, dehydrating, canning, and pickling. University extensions have plenty of resources, like this food preservation guide from the University of Minnesota Extension.

You can also save seeds for planting in next year's garden.

Keep a garden journal

One final thing after you've put your veggie garden to bed in the fall. Take photos of your garden all season—the good and the ugly. This visual reminder will be a huge help as you plan next year's garden. List your plants and what happened to them. If you found that 6 basil varieties were 4 too many, you'll want to remember that next spring. And share your experience. We’d love to hear about your gardening adventures!

How can I find my local cooperative extension service?

A fantastic resource for gardeners, cooperative extensions are affiliated with more than 100 land-grant colleges and universities. They provide a wealth of research-based information on gardening, farming, nutrition, food preservation and many other topics. Some extension websites are better than others, so browse patiently :)

To find your local extension, check out this list of cooperative extension websites.

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