A perennial question for many gardeners is whether or not to put a base or “bottom” in their raised garden beds. As an experienced gardener here in the lush landscapes of Wisconsin, I’ve experimented with both bottomed and bottomless beds over the years. There’s no definitive right or wrong answer – it truly depends on your specific climate, soil needs, and the types of plants you hope to grow. Dig deep and explore the pros and cons of bottoming your garden bed.
Contents
- 1 An Introduction to Fabulous Garden Beds
- 2 The Purpose and Advantages of a Bottomed Raised Bed
- 3 Potential Drawbacks of a Bottomed Raised Bed
- 4 Selecting Materials for Your Raised Bed Bottom
- 5 Constructing a Raised Bed: Step-By-Step Instructions
- 6 Alternate Options to Solid Bottoms
- 7 Answering Your Raised Bed Questions
- 8 Parting Advice for Your Raised Bed Dreams
An Introduction to Fabulous Garden Beds
For newcomers to the gardening world, let’s start from the beginning. A raised garden bed is a planting area that sits above ground, typically made of wood, stone, or brick. The bed is filled with a soil mixture specially formulated to provide proper drainage and nutrients for your vegetables, herbs, flowers, or other plants.
Raised beds boast many advantages: they minimize weed problems, provide excellent drainage if appropriately designed, allow for specialized soil mixes not native to the area, and are often elevated for easier access without compacting surrounding soil. They genuinely let your plants thrive with less fuss!
So that brings us to the excellent garden bed debate: to bottom or not to bottom? Simply put, a “bottomed” bed has a barrier acting as the floor at the bottom of the bed. This could be hardware cloth, weed barrier fabric, wood planks, stones, or any material that prevents direct contact between native soil and your raised bed’s soil mix. Bottomless beds lack this barrier, allowing plant roots to access the ground beneath the raised bed walls.
Explore the purpose and benefits of bottoming your raised beds while examining potential drawbacks. With this knowledge, you can decide what works best for your garden!
The Purpose and Advantages of a Bottomed Raised Bed
Bottoming your raised bed serves some essential purposes:
Keeping Burrowing Critters at Bay
In Wisconsin, I’ve dealt with my fair share of underground pests like moles, voles, gophers, and chipmunks burrowing under raised beds. Weasels, shrews, and even skunks can cause trouble too. Installing a physical barrier at the bottom of your raised bed blocks access from these underground burrowers.
Popular materials for barriers include:
- Hardware cloth or wire mesh
- Weed barrier fabric
- Stones, gravel, or drainage rock
- Solid materials like wood planks or concrete
This protects delicate roots and prevents pests from invading from below. Let your plants flourish in peace without those burrowing bullies!
Preventing Underground Weed Growth
Nothing is more frustrating than weeding a raised bed, only to have more weeds continually pop up from seeds buried deep in the soil under your bed. Lining the bottom blocks access so those nasty weed roots can’t sneak upwards. This makes maintaining your raised bed much more accessible.
Improved Drainage
Here in Wisconsin, soil drainage varies wildly depending on your location. And poor drainage causes a host of problems like stunted plant growth, diseases, pests, and mineral deficiencies. Lining the bottom of your raised bed allows you complete control over drainage and moisture retention.
Choose permeable materials like gravel, sand, or wood planks to improve drainage. Or use waterproof materials like concrete or plastic sheeting to retain moisture in quick-draining soils. Proper drainage provides the ideal moisture content for healthy roots!
Portability
Do you need to periodically move your raised beds around your yard to take advantage of seasonal sunlight? A bottom makes this easier and minimizes soil disturbance. Simply construct your raised bed with a solid base like wood or plastic sheeting. When it’s time to relocate, you can move the entire bed as one unit.
Tailoring Soil Conditions
Plant roots in bottomless beds grow into the native soil below the raised bed. While this provides anchoring, the native soil may be unsuitable for ideal plant growth.
Adding a bottom lets you completely customize the soil mix inside your raised bed without interference from native soil. Create the perfect balance of drainage, nutrients, and texture your plants need to thrive.
Potential Drawbacks of a Bottomed Raised Bed
Of course, along with the benefits, there are some potential downsides of adding a bottom to your raised bed that are worth considering:
Additional Upfront Costs and Labor
Any additional materials and construction time to add a bottom will increase the total cost of your raised bed. Being strategic with material choices can minimize expenses. For example, corrugated galvanized steel sheets provide an inexpensive impermeable barrier.
Consider the added cost as an upfront investment – you may save money and effort in the long run by reducing weeding and soil composition work.
Drainage Issues
As mentioned earlier, proper drainage is imperative for healthy plants. While a bottom can help control moisture, improper drainage design can also lead to waterlogging within the bed, causing issues like:
- Root rot
- Nutrient deficiencies
- Disease susceptibility
- Poor growth
Prevent this by using porous materials, adding drainage holes using an impermeable barrier, and grading beds with a slope to drain excess water. Rocks, sand, gravel, or wood planks are great for drainage.
Restricted Root Growth
Some research indicates that plant root growth can be restricted in raised beds with impermeable bottoms versus bottomless beds or traditional in-ground planting.
However, roots typically travel downward until they reach optimum soil conditions and moisture. In a properly designed raised bed with excellent soil mix, the roots won’t need to travel far to access their needs! Just be sure your soil mix offers sufficient depth.
Selecting Materials for Your Raised Bed Bottom
Plenty of material options exist if you elect to bottom your raised garden bed. Consider budget, longevity, permeability, and weight when selecting fabrics. Here are some of my top recommendations:
Durable Wood Planks
Wood is an attractive option that’s easy to install and suits many budgets. Cedar and redwood resist rotting well. Use thick planks with an angle or gaps to facilitate drainage.
Affordable and Effective Hardware Cloth
Hardware cloth is ideal for blocking pests and improving drainage. Opt for galvanized steel over aluminum, which can bend. Stainless steel offers strength and longevity. Overlap pieces during installation.
Long-Lasting Landscape Fabric
High-quality landscape fabric like woven polypropylene blocks weeds, retains moisture and lasts for years. Easy to install, it won’t decompose like burlap. Just be sure water can still drain through the fabric.
Low-Cost Plastic Sheeting
Use plastic sheeting like polyethylene film for a super affordable and readily available option. While it won’t last nearly as long as other materials, it gets the job done on a budget. Be mindful of plastic waste.
Fabric Pots
Try planting directly into large fabric pots or grow bags placed within a raised bed frame for a unique approach. The porous fabric allows drainage while containing the soil mix and roots.
Constructing a Raised Bed: Step-By-Step Instructions
Once you’ve weighed the pros and cons and decided on materials, it’s time for the fun part – building your raised bed! Follow these steps for a successful installation:
Planning and Design
First, map out your design – the size, shape, number of beds, spacing between beds, position, slope, etc. Consider factors like sunlight, proximity to water sources, and aesthetics. Make beds at least 4 feet wide to allow easy access for tending plants.
Next, select suitable materials that fit your gardening needs, bed style, and budget. Choosing quality materials upfront prevents frequent repairs down the road.
Preparing the Site
Check for underground pipes or wires. Remove any debris and level the ground where your bed will sit. If desired, lay a layer of weed barrier cloth over the native soil before installing your raised bed to impede weeds. Outline the footprint for your bed with stakes and strings.
Assembling the Bed Frame
Assemble your raised bed’s outer structure, ensuring components are level, corners square, and any hardware is installed securely. For wood beds, be sure to utilize corrosion-resistant screws.
Leave one side open if installing your bottom barrier after filling it with soil. Follow any specific assembly instructions for your chosen raised bed kit.
Installing the Bottom
Once the outer structure is in place, install your bottom barrier material. For example, if using landscape fabric, staple it to the inside of the wood frame bottom after cutting it roughly 2 inches smaller than the bed dimensions. Overlap adjacent pieces by 6 inches and work out any wrinkles or folds.
Soil Filling and Planting
With the bed structure and any bottom barriers in place, it’s time for the fun part – filling with nutrient-rich soil! Use a mix of compost, coconut coir, worm castings, and other amendments to optimize growth. Finish by transplanting seedlings or sowing seeds directly.
Alternate Options to Solid Bottoms
While traditional impervious materials are a popular choice for raised bed bottoms, you have other options too:
Loosely Laid Weed Barrier
Instead of stapling material firmly in place, you can lay landscape fabric, cardboard, or thick layers of newspaper loosely across the native soil before adding your soil mix. This still blocks weeds but allows better water permeability and root penetration. The barrier will degrade over time.
Bottomless Raised Beds
You can always elect to skip the bottom altogether! Allowing plant roots to access soil beneath the bed provides more nutrients. As mentioned earlier, roots typically won’t grow down farther than needed. Just beware of potential weed issues.
Partially Buried Raised Beds
Burying part of your raised bed sets the bottom slightly underground rather than sitting directly on top. This offers added stability and more insulation while allowing you to control soil composition.
Shallow Trench Lined with Rocks
Dig a shallow trench under where the raised bed will sit for improved drainage. Line the trench with gravel, rocks, or drainage pipe, then refill with soil. Excess water can drain out through the trench.
Answering Your Raised Bed Questions
Deciding on the ideal raised bed setup for your garden takes careful consideration. Let’s go over some of the most frequently asked questions:
Do raised beds need a bottom?
No, a bottom is optional. While it offers benefits like blocking weeds and controlling drainage, some gardeners opt for bottomless beds or alternate options like loose barriers. Evaluate your climate, soil, pests, and plants to decide what will work best.
What’s the best material for raised bed bottoms?
It depends on your goals. Landscape fabric excels at blocking weeds but reduces drainage. Gravel improves drainage but won’t block weeds well. Consider permeability, durability, and cost when selecting a bottom material.
Should raised garden beds be lined with anything?
Adding lining inside your raised bed offers many advantages, though it isn’t strictly necessary. Weed barrier cloth, cardboard, gravel, or hardware cloth can protect against weeds and pests while controlling moisture and drainage.
Can I just put a raised bed on grass or dirt?
Yes, raised beds can sit directly on grass or exposed soil. This is quick and easy. Remember that weed seeds and grass can germinate through the bed soil. Adding a loose bottom layer like cardboard can help block this.
How do I keep weeds out of raised beds naturally?
Use mulch on the soil surface and maintain consistent moisture levels to prevent weed seeds from germinating. Plants like thyme or chamomile grown around bed edges also deter weeds. For a natural barrier below the bed, lay down cardboard, layers of newspaper, or gravel before adding soil.
Parting Advice for Your Raised Bed Dreams
Whether you ultimately decide to bottom your raised bed or not, the most important thing is giving your plants the growing conditions they need to thrive! This will vary for each gardener based on climate, gardening style, and resources.
The joy of gardening comes from learning and experimenting – start small, track what works well for your space, and continue expanding your knowledge. Gardening should be a fun adventure! I hope weighing the pros and cons gives you the confidence to create your ideal raised bed oasis tailored to your needs.
If you try a new raised bed setup this season, please share photos with me! I’d love to see your impressive gardening skills in action. The gardens of Wisconsin can always use more beauty.
