We’ve all seen raised planter beds. They come in all shapes and sizes, teeming with flowers or greens or herbs or veggies. In the home-grower arena the raised planter is a great way to organize your gardens, control your soil, reduce pest influence and work more ergonomically. You can buy raised planters of all shapes and sizes, but if you are building your own there are some design considerations to keep in mind.
Basic Raised Planter Design Considerations
One of the biggest advantages to using raised planters is in bringing the plants closer to our level. Being able to work on the garden, check the soil, prune the plants and harvest without kneeling or bending over is a huge energy saver. Improved accessibility without having to be on your knees is a bigger deal for adults and kids with disabilities. When choosing the height for your planters, keep in mind the height of those who will be using the planter most. In general, 24 to 30 inches is a good height for average planters.
Special considerations should be made in your planter design for participants in wheelchairs. Access is incredibly important. For inspiration, or solutions, take a look at these planters by TERRAform specifically designed for gardeners in wheelchairs.
Just like the height consideration, width has to do with who will be using the planter as well as where the planter is located. We don’t want to make a planter so wide that it is difficult to see and reach plant material in the middle. Likewise, if the planter will not be accessible from all sides, you have to consider arm’s reach across the planter. A width between 18 inches and 2 feet is a good standard one-sided access for most users. If the planter can be accessed from both sides, double that.
What will you be planting in this raised bed? The depth of soil needed will vary depending on what you plan on planting. It would be wasteful to make a deep soil planter that will only ever grow leafy greens, the shallow root systems will never need more than about 6 to 8 inches of soil. However, if you’ll be growing tomatoes or peppers, you’ll struggle to grow a substantial and healthy root system in such a shallow planter. Some pre-planning here would go a long way toward your planter design.
Healthy garden soil needs proper drainage to allow for healthy root systems and maximum nutrient uptake. How you drain your planter will depend on a few things. First, is this an indoor planter or an outdoor planter? Indoors, obviously, you want to control where the water ends up to avoid a mess. Designing the raised planter to take drainage to one side or the other allows us to create a single point of escape for water and control where it goes. This also allows us to recycle the water and dispose of it in a productive way.
If the planter is outside, it also may be important to control the drainage so that the excess water can be used productively. We can also intelligently use planter drainage to gravity feed water to lower planters, making our watering efforts more efficient.
Either way, we know we are going to have excess water to contend with and that needs to be a consideration in the overall design of our raised planters.
Most of our raised planters will be made of wood. It’s the most common planters won’t hold our soil very well on their own and will need some sort of liner to hold the soil material in place. For indoor planters, the liner needs to be waterproof to allow us to have control over drainage.
For indoor planters, a simple landscape plastic might be too thin for long term use. It tends to puncture and break too easily. A 45 mil or greater pond liner would be more appropriate for long term, waterproof use and can hold up to manipulation and even the integration of pipe fittings. It also resists punctures from regular gardening tools and can be used for the life of the raised bed.
For outdoor raised planters, simple landscape fabric can be used to contain the soil but allow for water drainage and aeration. The landscape fabric is strong enough to contain soil and stand up to some abuse, but is water and air permeable. It’s an easy, affordable fabric that will allow for the easiest containment
Raised beds come in all shapes and sizes and a multitude of construction materials. Just about any material that will hold soil can be used as a planter. However, when we are building raised planters for the growing of edibles there are a few considerations we need be aware of.
The most important is the potential for chemical leaching into the soil from contaminated materials. Treated woods, concrete and plastics are common materials that have a potential to contaminate soil over time. It is important that the materials used in building your raised beds be clean and untreated. Old, reclaimed boards are an attractive and creative material tempting to use for raised garden beds, but it’s nearly impossible to insure they are free of chemicals or old lead-based paints.
Galvanized tubs and stainless steel can be used for planters but they can also get too warm in direct sun and overheat soil. Untreated metals, even galvanized metal, is also susceptible to rust and corrosion which can taint soil.
The safest material to use in building raised beds is new, untreated lumber. For outdoor planters, cedar, black locust and redwood are good choices because they will wear well and hold up to weather. Doug Fir is also a good, and more affordable, option but may not hold up as long.
NOTE: When choosing wood, BE SURE to use untreated wood. In 2003, the EPA banned the sale of lumber treated with chromated copper arsenate (CCA) for residential use. Two compounds, alkaline copper quat (ACQ) and copper azole (CA-B), have now replaced CCA wood in the residential market. Both contain copper and a fungicide but no arsenic. The copper keeps insects at bay, and the fungicide prevents soil fungus from attacking the wood. In ACQ, the fungicide is quat, which is also used in swimming-pool chemicals and as a disinfectant. The other compound, CA-B, uses copper and tebuconazole, a fungicide used on food crops. According to Miles McEvoy, who works in organic certification with the Washington State Department of Agriculture, no pressure-treated wood is allowed in soils used to grow organic food. If you want to meet this high standard, choose a different material. (source)
The Benefits of Raised Planters
- Control over soil
- Ability to grow indoors
- Accessibility for folks with bad knees
- Can be used as design elements on patio
- Vessels for growing in confined or urban spaces
- Easy to weed
- Reduced compaction
The Challenges of Raised Planters
- Moisture control
- Nutrient control
- Soil temperature control
- Maintaining proper pH level