Bottom watering is a highly effective technique for hydrating potted plants by supplying water from below. This process allows the soil to absorb moisture upward through the drainage holes, encouraging a controlled and thorough soaking of the entire root ball. Unlike pouring water onto the soil surface, which can cause uneven saturation or runoff, this method prevents common issues associated with overhead watering, such as soil compaction and certain fungal diseases. This simple shift in practice can lead to noticeably healthier growth for many indoor species.
Understanding How Bottom Watering Works
The success of this watering method relies on capillary action, the natural phenomenon that allows water to move upward against gravity. When a potted plant is placed in a tray of water, the soil acts like a sponge, drawing moisture upward through the air spaces between the potting mix particles.
Capillary action occurs due to the cohesive forces between water molecules and the adhesive forces between water and the soil medium. Water molecules cling to soil particles and pull others along, effectively wicking moisture from the saucer to the top layer of soil. This process ensures uniform saturation of the potting mix, guaranteeing hydration for all roots. It also promotes deeper root development as roots grow downward to seek the consistent moisture source.
This sub-irrigation technique helps to maintain soil structure by avoiding the downward force of water that causes surface compaction. Keeping the top layer of soil relatively dry also minimizes the damp environment where common houseplant pests, like fungus gnats, prefer to lay eggs. The plant should soak for 15 to 30 minutes until the top layer of soil feels damp, then be removed, and any excess water discarded.
Characteristics of Plants That Benefit
The most suitable candidates for bottom watering possess specific physical traits or are susceptible to moisture-related ailments. Plants with dense or fuzzy foliage thrive because this method avoids contact between water and leaves, preventing spotting or rot. African Violets are a classic example; their velvety leaves and low-growing crown are prone to fatal crown rot if water sits on the foliage.
Plants with a compact growth habit, where leaves form a tight rosette or canopy over the soil, benefit significantly because top watering is physically difficult. Species like Peperomia and some Calathea varieties have densely packed foliage, making it challenging to water the soil without spillage. Bottom watering ensures the root zone is thoroughly moistened without disturbing the plant’s structure.
The even saturation achieved through capillary action is also highly beneficial for plants that prefer consistently moist, but not soggy, soil conditions, such as Peace Lilies and Ferns. Ferns, in particular, appreciate the steady moisture without their delicate fronds being damaged by overhead watering. Furthermore, bottom watering is excellent for rehydrating potting mixes that have become excessively dry and hydrophobic, which often occurs with peat-based soils that repel water when desiccated.
Plants Where Bottom Watering is Not Recommended
While bottom watering is a valuable tool, it is not the best long-term solution for all plants or situations. The primary drawback is that it does not allow for the natural flushing of the soil, which is necessary to remove accumulated mineral salts and fertilizers. Since water moves upward and evaporates from the soil surface, it deposits these dissolved solids at the top, where they can build up over time.
This mineral accumulation can lead to “salt burn,” causing the plant to struggle to absorb water and nutrients, often resulting in browning leaf tips and edges. Even for plants that regularly benefit from bottom watering, it is necessary to flush the soil by top watering until water runs freely out of the drainage holes approximately once a month.
The method is also inefficient for extremely large or deep containers, such as those housing established trees or large shrubs. The time required for capillary action to fully saturate a massive volume of soil can be excessive, making top watering the more practical choice. Additionally, bottom watering is less effective when soil is heavily compacted, as the lack of adequate air pockets hinders the necessary capillary movement of water.