When it comes to greenhouse flooring, you have several choices. Before you rush out and buy the first material that comes to mind, consider the pros and cons of each. Analyze your budget and specific needs, then choose accordingly.
Gravel: I’ve laid down 6 inches of gravel in my greenhouse because I like how well it drains. Plus, it’s relatively cheap. However, some gardeners may find loose gravel “unstable” underfoot, and may opt for crushed rock (with jagged edges that resist movement) or a more solid floor, such as…
Brick: Pricey, but beautiful. Tolerable drainage capacity, since water will find its way through the cracks. Bricks also will absorb and retain heat better than any other flooring material, releasing it slowly during the first hours of darkness and extending the period of warmth inside your greenhouse.
Sawdust, bark, wood chips: Very cheap — sometimes free, if you know where to look! My dad used sawdust for his greenhouse floor and thought it worked just fine. These wood-based materials, however, are organic, so they will break down over the years and need replacing.
Wood planking: This will give your greenhouse floor a gorgeous finished look, but price might be a factor. If you have more money than I, you might decide to use an insect- and rot-resistant species, such as redwood or ipe, or lay down treated wood decking — like my dad did after mom got tired of the sawdust. If money is no object, use composite wood, which will never rot or succumb to carpenter ants or termites.
Stone: Pricewise, a flagstone floor in your greenhouse will run in about the same neighborhood as brick, and will offer close to the same heat-retaining properties. Drainage shouldn’t be an issue, although you might get some puddling on larger stones. What a beautiful look!