A flower pot filler is material placed in the bottom third to half of a large container before adding the potting mix. The primary purpose of using a filler is to reduce the volume of potting soil required for oversized planters. This practice also significantly decreases the overall weight of the container, making it easier to move for seasonal changes or landscaping adjustments. Fillers are useful in large, deep pots where the plant’s root system will not extend to the very bottom.
Acceptable Household and Recycled Fillers
Non-biodegradable, lightweight household items are excellent choices for pot filler because they will not break down over time. Empty plastic water bottles with securely fastened lids are highly effective, as the trapped air provides maximum volume displacement with minimal weight gain. Clean, empty milk jugs and larger plastic containers, such as inverted plastic nursery pots, also work well to occupy large portions of the planter’s base.
Styrofoam packing peanuts are another popular, lightweight option, but ensure they are the non-biodegradable type, as water-soluble versions quickly dissolve. These materials are inert and will not interact chemically with the soil or plant roots. Using these recycled materials is a simple way to save money on potting mix while repurposing items that would otherwise be sent to a landfill.
Natural and Organic Materials
Materials sourced from nature or garden waste offer an eco-friendly alternative for filling large flower pots. Examples include pinecones, dried leaves, chipped bark, or untreated wood scraps. These organic fillers will eventually decompose, providing minimal nutrients to the soil over time.
The decomposition process is a major consideration because it causes the filler material to break down and compress, leading to soil subsidence. The level of the potting mix will gradually drop over time as the material decays and settles. Gardeners using organic fillers must periodically add more potting mix to maintain the appropriate soil level.
Materials to Avoid
A common mistake is adding a layer of rocks, gravel, or broken pottery to the bottom of a container to “improve drainage.” This practice actually hinders proper water flow and can be detrimental to the plant’s health. Water will not readily move from the fine-textured potting mix into the coarse-textured gravel layer due to the concept of the perched water table.
The perched water table is a layer of saturated soil that forms just above the coarse-material layer. Capillary action holds the water in place, resisting the force of gravity that would normally pull it down into the gravel. This results in the soil remaining saturated, which deprives the roots of oxygen and leads to root rot. Materials that break down quickly or absorb water should also be avoided, such as sponges, glossy paper, or treated wood, which can leach unwanted chemicals into the soil.
Proper Technique for Placement
Before adding any filler, confirm the pot’s drainage hole is clear to allow excess water to escape freely. The filler should occupy approximately one-third to one-half of the container’s total volume, ensuring sufficient space for the plant’s root ball and adequate potting mix depth. It is recommended to provide a minimum of 12 inches of potting mix above the filler for most annuals and small perennials.
A barrier layer should be placed directly over the filler before adding the potting mix. This prevents the soil from sifting down and clogging the gaps between the filler items. Landscape fabric, a piece of window screening, or an old t-shirt can serve as an effective barrier. This layer keeps the filler stable and separate from the potting mix, simplifying the process of changing the soil or repotting the plant.