How to Build a Raised Bed Foundation for Your New Greenhouse

Building a greenhouse foundation bed

Whether you want to get a standalone or a lean-to greenhouse, you must ensure you get the basics right.

Choosing the most suitable greenhouse foundation is essential for achieving structural stability. However, most gardening lovers lack basic knowledge about the prerequisites of greenhouse installation.

 Its foundation can make or break your greenhouse gardening experience and impact your kit’s overall safety and stability. Today, we’re talking about raised bed greenhouse foundations commonly known as stem walls and their role in improving a greenhouse’s structural integrity.

Continue reading to learn more about raised bed greenhouse foundations and the steps involved in building them.

What You Need to Build a Raised Bed Greenhouse Foundation

Here is everything that you’ll need to kick-start your raised bed greenhouse foundation-building process:

  • Water-based preservative-treated wooden boards for creating the walls. Make sure the timber panels are cut exactly into your desired size. We recommend you pre-specify the size of a greenhouse you’re interested in buying for a spot-on foundation.
  • Cloche sides, ends, and hoops to tie up the timber in a desired shape
  • PVC clips, galvanized steel screws, pipe straps, a hand saw (for resizing), and a drill or screwdriver. We recommend you use a drill for faster and more secure fastening.

A person making a wooden panel for a greenhouse foundation

Wooden raised beds or stem walls for greenhouses are extremely popular in the DIY greenhouse community, but you can also opt for a base material for your greenhouse foundation. Follow these key steps to assess which base is perfect for your greenhouse:

  • Pick the right greenhouse orientation, preferably the southern side
  • Choose a base according to the wind and snow load of your greenhouse. Refer to the greenhouse manufacturer manual for these values.
  • Try opting for a tie-down kitfor securing the greenhouse base for maximum sturdiness and weather impact resistance
A greenhouse on a raised wooden base

Building a stemwall is the most effective way to elevate a greenhouse, and a good way to do it is to purchase a drop door kit to lower the door for easy access. However, you'll have to fill the gap that is above the door by purchasing glazing from your local store.

Find the perfect drop door kit here.

Greenhouse Raised Bed Foundation Size Considerations

The size of your raised greenhouse foundation depends on the greenhouse itself. However, knowing certain standard practices can help you ensure maximum efficiency;

  • A raised foundation can be as tall as 36 inches. Most gardeners opt for a height between 11 and 15 inches that usually comprise 2 stacked wooden panels
  • If you’re preparing a raised foundation on a soil bed, consider a lower height of up to 6 inches to allow roots to easily penetrate the surface
  • Don’t exceed the height limits too much, as the soil in the cavity the push the side walls outwards
  • Add cross-support panels in taller raised beds for structural safety
  • It’s also useful to assess the kind of plants you will grow inside your greenhouse and set the raised bed’s height accordingly. Learn the soil depth requirements for various popular greenhouse plants here: Soil Depth Requirements

EPA’s Instruction on Treated Lumber for Raised Bed Greenhouse Foundations

When building a wooden raised bed foundation for your greenhouse, follow EPA’s instructions about treated lumber. The energy authority has banned the sale of treated lumber to residential buyers due to its hazardous composition. Most sellers treat their lumber with chromate copper arsenate, which poses cancer and non-cancer health risks.

The said chemical compound is now replaced by a safer substance that prevents rots and soil fungus attacks. EPA also suggests residential greenhouse users use recycled composite plastic lumber as a safer, more efficient alternative to real wood lumber.

A stem, wall lean-to greenhouse

Types of Bases for Creating a Raised Bed Foundation for Your New Greenhouse

Now that you have figured out the necessary tools and tips required for choosing and building a greenhouse raised bed foundation, let’s delve deeper and discuss its different types:

1. Wooden Base

A wooden raised base for your greenhouse can be an excellent choice, especially if you intend to install a greenhouse on an existing deck space. Choose rot-resistance and naturally durable wood such as timber to prepare this greenhouse foundation. Based on your chosen wood and greenhouse size, a wooden raised bed will cost you around $25 per square foot.

A greenhouse in an altitude area

2. Concrete Base

A concrete raised bed for your greenhouse is the most durable and sturdiest foundation option. While it required planning and labor ahead of time, but also proved quite fruitful in the long run. A concrete base is more permanent. Hence, you should ensure the correct positioning before starting. The height of your raised concrete base can be adjusted according to your preference.

However, don’t opt for a concrete base for greenhouses bigger than 8ft x 10ft, as they can push the base down the ground in wet weather. We recommend creating a solid concrete base before building the sidewalls for maximum practicality and functionality. This option will allow you to install larger greenhouse structures easily.

3. Block-Raised Perimeter AKA Stem Wall

As the name suggests, a perimeter greenhouse base doesn’t extend down the ground and basically sits on the surface as a raised wall. You can use breeze blocks, slabs, or bricks to create a perimeter base. However, it’s only suitable for small greenhouses due to their lower weight holding capacity.

Riga greenhouse installed on a raised perimeter

How Mulberry Greenhouses Can Help You

Greenhouses are one of the best inventions that have slowly yet steadily revolutionized gardening and farming practices worldwide. First created in the 1700s, greenhouses have become a top choice for adopting easier, safer, and cleaner growing techniques. Everyone from home gardeners to farmers is trying to make the most of a greenhouse’s safety and efficiency.

So if you’re looking for anything related to greenhouse building, updates, and gardening, Mulberry Greenhouses can help. We provide original greenhouse kits and greenhouse accessories in the US. Our focus on quality translates into our stellar market reputation and customer loyalty.

Learn more about our products here, or check out our greenhouse guides for more information.

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