Most landscape professionals know that planter gardening can be quite different when compared to regular gardening directly in the ground. From watering requirements to nutrient requirements, and even the soil type itself, in planters, can be quite unique.
Fiberglass planters, when compared to other planter materials, can make planter gardening much simpler from a winter maintenance perspective. Simply stated, a good quality fiberglass planter can remain as is, where is, over the winter. The two key factors in the survival of the planter itself without winter damage is drainage and soil type.
Water must be able to drain sufficiently from the planter as the freezing weather approaches and subsequently takes hold. Water, as it freezes, expands considerably with a significant force. Water that remains in a confined space will break through that confinement, meaning that it will easily crack a planter, fiberglass or otherwise. If that water can drain, then it simply isn’t there to freeze, expand and ruin the planter. The soil can be moist, and yes, it will harden with the freezing temperatures, but there will not be enough water in a well-drained soil to expand significantly enough to do any damage.
And one great advantage of fiberglass is that it is not porous, so water cannot seep into the walls and then freeze and do damage.
The second factor is the soil. Planters should always contain a lightweight potting soil. Never clay, never shovelfuls of whatever soil was found in the garden, and not even a topsoil. The idea is that a lightweight potting soil can drain well before freeze-up.
Whether the plants are removed will depend on what plants have been planted. For perennials that remain in the planter on a year-round basis, nothing else needs to be done. Everything freezes and then everything thaws and the cycle starts again. In select cases, prior to the original planting, a rigid or spray foam insulation can be placed up against the planter inside walls. This is intended to keep the roots frozen and protect the plants from starting a new premature growth cycle during a winter thaw, followed by a deep freeze, a sure way to distress and even kill the plant.
And of course, leaving a planter outdoors on a year-round basis with UV exposure requires good UV protection to prevent fading. Good quality fiberglass planters will have excellent UV protection. But remember, the old saying of “you get what you pay for” is true even with planters. Cheap planters probably have no UV protection so expect fading.
Come the spring, let the planter and contents thaw thoroughly, wipe it down with some warm water and possibly a little detergent, dry it off, and you’re ready for another season.