26 Decomposition Organic materials such as bark mulch, sawdust, and wood will need regular replacing. These tend to decompose and becoming a breeding ground for algae and pests and the cost savings will become prohibitive in the long term when you need to remove and replace the rotting floor. Price The cost of flooring materials is by far one of the most important factors to consider when selecting between greenhouse flooring options. A full concrete slab is up to your discretion. You should plan to power wash the concrete with each annual cleaning to ensure that algae are not forming on the surface. For most areas, gravel is the most cost effective floor covering that has the most benefits in the greenhouse. Heat Retention Heat retention is an important factor in the greenhouse if you live in a colder climate. A concrete slab and most materials such as brick and flagstone will help trap and slowly release the day’s heat dur- ing the cooler nighttime hours. This can help decrease your heating costs during colder weather. Bark mulch flooring.