Home gardening often relies on standard containers, and the five-gallon pot is a popular choice for growing everything from large vegetables like tomatoes to small ornamental shrubs. Accurately determining the volume of growing medium needed is a practical first step for planning and purchasing supplies. This calculation prevents unnecessary trips to the garden center and ensures your plants have the correct amount of material for optimal growth.
Exact Soil Volume Needed
A standard five-gallon container holds five US liquid gallons of volume, which is the baseline measurement. For home gardeners, the required volume is most often expressed in quarts or cubic feet, the units in which potting mixes are typically sold. The total volume converts to approximately 20 quarts or roughly 0.77 cubic feet of material.
Potting mix is sold by volume, not weight, and the actual amount needed may be slightly higher than the container’s exact capacity. This difference accounts for the settling and compression that occurs after the container is filled and thoroughly watered. Planning for a small amount of extra material ensures you can top off the container after the initial settling process.
Selecting the Ideal Potting Mix
The success of container gardening hinges on using a specialized potting mix rather than garden soil. Soil taken directly from the ground is unsuitable because its fine mineral particles compact easily in a confined space. This compaction prevents proper aeration, which is the movement of oxygen to the roots, and leads to poor drainage.
A quality soilless potting mix is engineered to remain light and porous even when wet, promoting the necessary air exchange for healthy root development. These mixes contain components that balance moisture retention with rapid drainage. Peat moss or coco coir are included to absorb and hold water, releasing it slowly to the plant.
Aeration and drainage are primarily provided by inert materials like perlite or vermiculite. Perlite, a puffed volcanic rock, creates microscopic air pockets that keep the mix from becoming dense. Specialized mixes for vegetables or succulents adjust these ratios, often containing more compost for nutrients or more perlite for faster drainage, respectively.
Step-by-Step Potting Technique
Before adding any medium, ensure the container has unobstructed drainage holes at the bottom to allow excess water to escape freely. Placing a layer of gravel or broken pottery at the base of the pot is a common but counterproductive practice. This layer actually raises the “perched water table,” bringing the saturated zone closer to the plant’s roots and increasing the risk of root rot.
The correct technique is to fill the entire container directly with the chosen potting mix without any bottom layer. When filling the pot, avoid pressing or compacting the medium, as this immediately defeats the purpose of using a light, well-draining mix. Simply pour the mix in and gently settle it by tapping the pot on the ground once or twice.
Proper technique requires leaving a specific empty space, known as headspace, between the surface of the potting mix and the rim of the container. For a five-gallon pot, this space should be about one to two inches deep. This reservoir prevents water from running over the side during watering, allowing it to soak evenly into the entire volume of medium.