What to Consider When Choosing a Greenhouse Foundation

When considering building a backyard greenhouse, another important factor, second only to the framing, is the foundation.  The foundation of your greenhouse is very important to the overall health of the plants you grow in it.  Here’s why.

First of all, you must decide if your greenhouse should sit on a permanent foundation, or if you want it to be semi mobile.  This is an important consideration if you want to grow certain plants year round as the quality and quantity of the sun that is available will change with the seasons.

Secondly, the material that the foundation is constructed out of will have certain characteristics.  For example, a concrete foundation will be porous and will hold onto a certain amount of water every time the plants are watered or the floor is cleaned.  This becomes important when trying to regulate the relative humidity in your greenhouse.  Plus concrete requires a little maintenance from time to time as the expansion and contraction process the concrete experiences daily will eventually create small cracks that will need to be patched.  And, since concrete is porous, there is a tendency for weeds, fungus and bacteria to take hold and grow.

Synthetic materials do not experience any of these problems, but have several of their own.  PVC and plastic are not porous materials, meaning that they will NOT absorb any water at all.  This can be a bit of a hassle during routine cleaning, as the floors will need to be carefully dried to prevent bacteria from growing, or from excess humidity problems.  Synthetic floors are not as strong as concrete and can eventually bend and crack if exposed to excessive weight for long periods of time.   And, since water is not wicked away, the surface can become quite slick.

Both materials however do have their redeeming qualities, though.  PVC and plastic come in a myriad of colors, are readily available in most markets and are easy to install and maintain.  Plastics are lightweight and easy to move in the event that the greenhouse ever needs to be relocated.  Concrete is a bit tougher, since forms have to be made, proper mixing techniques must be used, and it takes a while to become hardened enough to build on, but the end result is a sturdy, easy to clean, permanent foundation on which to build your greenhouse project.  Concrete is usually less expensive than plastic as well.

Metal floors can be used, but they are much less common because no matter what the climate conditions are, greenhouse floors and exposed to a great deal of water.  Metal floors tend to oxidize over time, rusting the metal and creating weak spots in the floor that will require replacing.  Metal floors can be somewhat more difficult to install and, though they are not considered a permanent foundation, are relatively difficult to move.

Consider the foundation of your new greenhouse very carefully before beginning your build.  It may be the most important decision you make.