16 Raised Garden Mistakes You Might Be Making (And Solutions To Fix Them)

There's something rewarding about plucking fresh herbs to accent your pasta sauce or crisp lettuce leaves for an impromptu salad. For many homeowners, though, the thought of tilling the land and maintaining an in-ground garden seems overwhelming. Raised beds let you tiptoe into gardening with various setups available, whether you buy a premade kit or build a bed from scratch. Gardening in raised beds gives you control over the soil quality, makes it easier to manage irrigation, and allows you to tend beds without doubling over. But despite being relatively beginner-friendly, raised bed gardening isn't foolproof. 

Being aware of common mistakes, like building beds too wide or too tall, can help you achieve success faster when you're starting a raised bed garden. It's important to use safe building materials and a quality soil mix without the wrong kind of filler. Placement is also key — avoid putting your beds in a spot that blocks traffic or doesn't offer the right conditions. And while you can grow almost any type of plant in a raised bed, you can make mistakes on what you plant together and the positioning. 

Pallets, railroad ties, and other previously used wood products offer an affordable (and sometimes free) building material, but they aren't generally safe for building beds for edible plants. Chemicals are sometimes applied to pallets to keep insects away, and some of those chemicals are toxic, including methyl bromide. It's possible that pallets once held chemicals or other items that contaminated the wood and could leach into soil. Railroad ties are treated with creosote, which can kill plants, but only if the wood still smells heavily of creosote or is oozing black, sticky goo. 

To avoid contamination, build raised planters from untreated wood, ACQ ground contact treated wood, bricks, or concrete blocks. Lumber treated with ACQ adds copper to the soil, which is an essential nutrient — however excessively high levels could have adverse effects on plants. Wooden raised garden beds have some disadvantages, including rotting and maintenance needs, but wood is naturally insulating and cedar planks offer extra longevity. If you already have a raised bed made of questionably treated wooded, empty the soil and add a thick plastic liner. Then, refill the bed with fresh soil.

Size is an important factor when building your bed. You want to maximize the space, but the width affects how easily you can care for your plants. An overly wide planter makes it difficult to reach the middle to handle weeding, irrigating, and harvesting crops. The typical person can only reach about 2 feet, so beds that are 5 feet wide or larger won't be easily accessible. The length of the bed is more flexible and is often based on the available space. Eight feet is a common length, but you can adjust the size based on your yard.

When planning your design, limit the width to 4 feet. You'll want to make the bed even narrower — no more than 2 feet wide — if you place it against a building or another structure where you can't access it from both sides. Consider your mobility and how far you can reach when planning the bed size.

The height of raised beds impacts drainage, accessibility, and construction costs. Building a tall bed needs extra material and more soil. However, a barely raised bed requires you to bend over to reach the plants, and it doesn't provide as much room to amend the soil. It also keeps plants low to the ground where animals and pests can reach them easily. The types of plants you grow (and how deep their roots go) can also affect how tall to make the bed.

If you just want increased drainage, build raised beds at least 6 inches high. However, it's common (and often more practical) to build beds between 18 and 24 inches tall. To determine how deep your raised garden bed should be, decide what you'll plant and how far you're willing to bend down to tend it. Plan a bed that's at least 12 inches deep for carrots, potatoes, squash, tomatoes, and other plants with deep roots. You can get away with a 6-inch-deep bed for veggies with shallow roots, like lettuce. If you put your raised bed over concrete, making it deeper allows for better drainage.

Placing a raised bed on a slight slope might not seem like a big deal, but it can affect the health of the plants in the bed. An slanted bed can allow water to collect in one end, causing uneven irrigation. The soil can also shift, resulting in ruts or displacing soil around plant roots. Raised beds might not be level if you build them on a slope or if you're not careful while building the bed.

Make a visual check of the area you're considering to see if it looks level. Checking with a bubble level can confirm whether or not the ground is level. If the location of the raised bed is on a slope, you can dig out soil to lower areas or fill in sunken areas to create a smooth surface. Check the raised bed as you build it, verifying that it's level before you fill it with soil.

It makes sense cost-wise to scoop regular garden soil that's already available into a raised bed. The native soil might work well for the trees, grass, and landscaping planted in the yard, but it's not ideal for raised beds. Soil from the ground is typically heavier, which isn't ideal for raised beds or container gardening. It could also contain pathogens, pests, and weed seeds that you don't want to introduce into your confined gardening beds. Some areas also have poor soil, such as heavy clay that doesn't allow proper drainage or compacted soil that prevents roots from growing well, which isn't ideal for planters. One of the big perks of raised beds is having control over the soil to ensure it drains well, has great structure, and is high in nutrients.

The solution is to buy or create a high-quality soil mix that supports healthy plant growth in a container. One option is using a 50/50 mix of topsoil and compost, blended together. Another suitable soil mix is equal parts of topsoil, compost, and coarse sand for a light medium that drains well. You can use well-rotted manure or peat in place of the compost as your organic matter in the mix.

Being able to place a raised bed anywhere on your property is one of the advantages of this option, but that doesn't mean you should position it haphazardly. The plants in a raised bed still need ideal growing conditions, which means getting adequate sunlight. Vegetables typically need full sun to grow well. Ignoring their light requirements and placing a raised bed in a shady area will likely result in a reduced yield or plants that don't grow well.

Choose a spot that receives at least six hours of light every day if you're growing vegetables. More is ideal, but six should work for many plants. When full sun isn't an option, prioritize spots with morning sun over those with afternoon sun. Consider plant location within the bed, putting taller plants toward the north end and shorter plants at the south to ensure your crops don't shade each other.

While sunlight is important to the bed placement, so is accessibility and traffic flow. Raised garden beds require regular care, especially when the weather is dry and hot and the plants need to be irrigated frequently. Raised beds tend to dry out faster than in-ground gardens, so you could be watering frequently, making water access crucial. If you place the bed too far away from the house, you might forget about it or find gardening less enjoyable. But parking it too close to the house or entertainment areas could interfere with the traffic flow and your regular outdoor activities.  

Check the distance from your outdoor spigot or faucet to the gardening bed to determine how easy irrigation will be. If you don't have a hose that's long enough, you'll have to carry water in a watering can back and forth, which could take multiple trips for large beds. A spot close to the house, along a path, or with open space on all sides makes access easier. Consider the types of activities people do in the yard, and find a spot where the beds will be out of the way.

It's common to place multiple raised beds in the same general zone, especially if it's a nice level area that receives lots of sunshine. But in your efforts to maximize the space, don't squish the beds together too close. Without an adequate walkway, it's difficult to reach the beds and navigate through them comfortably. It's also more challenging to fit equipment, like wheelbarrows, between the beds. Even hauling bags of fertilizer or baskets of harvested produce will be trickier if the walkways are narrow. 

Position beds a minimum of 18 inches apart to leave plenty of room for access. However, it's best to space the raised beds at least 3 feet apart if you want to push a wheelbarrow between them. If you garden from a wheelchair, leave wide enough pathways to accommodate your wheelchair with extra space on both sides. Manual wheelchairs typically range from 25 to 36 inches wide, and power wheelchairs may measure between 23 and 32 inches wide. To plan the placement, use graph paper to sketch the area, showing the beds and the walkways between them.

It's tempting to try to maximize container gardening space is by planting crops close together. But overcrowding is an overlooked mistake that could make your garden beds look bad and impact growth. That tiny tomato seedling will expand quickly and could crowd out other plants or cast too much shade on veggies that need plenty of sunlight. It's common to space plants close together in a container garden, but make sure to give each plant enough room for its roots and the upper portion to grow.

Research how much space each crop needs. For instance, tomato plants usually require at least 18 inches, but indeterminate tomato plants may need 2 feet or more. Square-foot gardening is a popular option — it involves splitting the garden into 1-square-foot sections and planting something different in each square. You may need to use multiple squares for larger plants, or be able to interplant multiple smaller vegetables (like radishes) into a square.

Planting food your family eats makes sense, but it's not always the best choice to throw a bunch of random plants together in one bed. Some plants don't make good neighbors due to different growing needs or characteristics that impair the other plant. Other potential issues are placing plants together that are both heavy feeders, share the same common pests, block shade, or release chemicals that negatively affect each other. For instance sunflowers produce what's known as allopathic chemicals which can inhibit the growth of other plants, so you'll want to be wary of planting these into raised beds where you want to grow vegetables. Vining plants can be incompatible with other crops because they can take over the entire bed.

As you're planning your garden, make sure the crops you choose make good companions. Companion planting can benefit your garden by pairing up plants whose growth habits and needs are similar. For example, radishes, onions, strawberries, and carrots can be good companions for lettuce. Given the proper spacing, they can all grow happily together without shading each other out, rambling over each other, etc. 

Planting the same crops in the same raised garden containers could result in declining outcomes each year. Elevated containers can harbor diseases and pests in the soil, which can infect future crops. Also, if you plant crops from the same family the following year, they might not have enough nutrients available to thrive, or they may suffer from pests and diseases.

An easy solution is to rotate your crops each year. Wait at least three to four years before you plant them there again. But it's not just one specific crop you want to avoid repeating — it's the entire family. For instance, the nightshade (or Solanaceae) family includes peppers, tomatoes, potatoes, eggplants, and tomatillos, so you want to avoid planting all of those items in the same bed from year to year. To manage crop rotations, keep a spreadsheet or garden journal documenting what you plant in each bed.

Technically, you can plant anything in an elevated bed. On a practical level, larger plants that have deep roots or need lots of room to expand or vine will be space hogs. Corn gets tall and could block sunlight from lower plants, and it grows better in multiple longer rows for better wind pollination. Meanwhile, asparagus requires a deep, complex root system to thrive, which usually isn't possible in a closed-in area. Some herbs, like horseradish and mint, spread aggressively and take over the garden.

Avoid growing plants in raised garden beds that spread or take up lots of space. If you grow tall crops, like corn or vining produce, position those items at the north end of the bed. That way, they won't block the sunlight from the other plants. Include supports for vining plants to help them grow upward, and use tomato cages to contain the sprawl of your tomato plants.

Tree roots are shallow and wide, sometimes stretching as large as three times the spread of the tree's canopy. And those roots largely stay close to the surface — most are no more than 18 inches deep, and about half are in the top 6 inches. Even smaller trees could eventually reach your beds. Roots near your elevated gardens can steal nutrients and water from the plants, and they could shift the structure of the garden. Since the tree is also looking for nutrients, the roots might naturally be drawn to your well-maintained garden areas.

When possible, position your planters far from trees. If tree roots are growing into your bed, you can dig them out, but they'll continue to grow. Too much cutting could also damage the tree. Adding a metal or plastic barrier at least 2 feet deep between trees and the planting bed could redirect roots. You can also pull up the raised bed and place it on a concrete slab to keep the roots from infiltrating.

Elevating your gardening beds causes the soil to heat up faster, and it also dries out faster. Failing to water your raised bed regularly is a mistake you want to avoid. At the same time, you can still overwater plants in a raised garden, which can lead to root rot and stunted plant growth.

Soaker hoses or drip irrigation makes it easier to keep the soil consistently moist based on the watering needs of the plants in the bed. It's best to water plants at their bases instead of overhead as damp leaves can increase the risk of disease. Watering requirements can vary, but plants in a raised garden usually need 1 to 2 inches of water total each week. If your plants wilt, it typically means they need more water. Yellowing, rotting at the crown, and stunted growth can be signs of too much water and indicate that you need to ease up.

You might get so excited about your garden that you want to plant as much as possible. For beginners, starting small is often a less overwhelming option. Not having enough time or plant knowledge to care for multiple beds fully could lead to poor results and wasted money on plants that don't mature. While raised beds are often easier than in-ground gardens, they still require adequate care, which can be time-consuming. Building raised beds also involves a fair amount of resources, whether that be time spent constructing them, money for the materials, or quality soil and compost to fill them with. 

Evaluate your gardening skills honestly — if you're a beginner, starting with one or two raised beds allows time to learn about proper plant care, and requires less work and money upfront to set up. Consider your schedule and available time. Busy homeowners without enough hours to devote to weeding, watering, fertilizing, and pest control may want to stick with one bed. Also, consider your goals. One bed is often enough to supplement grocery shopping.

The height of raised beds means you need a lot of filler, and there are many items you shouldn't be filling a raised garden bed with. Rocks can make it difficult to dig too deep, and they can prevent adequate water drainage. Plastics and foams could leach chemicals into the soil, and become a source of microplastics — which, at high concentrations, can be detrimental to soil organisms and plant growth — making items like pool noodles a bad idea.

When possible, limit the depth of your bed so you can fill it primarily with your soil mix. If you need additional fillers, choose organic materials that will break down and add nutrients. The lasagna gardening method layers cardboard, yard waste, straw, compost, and other organic materials. Avoid anything that won't break down or that will contaminate the soil.