Bottom watering is a popular technique in houseplant care where a plant absorbs moisture from a tray or container placed beneath the pot. Water is drawn up through the pot’s drainage holes, allowing the plant to take up only the amount of water it needs. This efficient method raises a fundamental question: can every plant be watered this way? While bottom watering offers numerous benefits for many common houseplants, the answer depends on the underlying physics and specific plant requirements.
How Bottom Watering Works
The effectiveness of bottom watering relies on capillary action, the ability of a liquid to flow in narrow spaces against gravity. In the soil, water molecules adhere to soil particles (adhesion) while clinging to each other (cohesion). As water is absorbed through the drainage holes, these forces pull moisture upward through the pores and channels within the soil column.
This upward movement ensures the entire soil mass is evenly saturated, unlike top watering where water can channel down the sides, leaving dry pockets. Drawing moisture deep into the pot encourages roots to grow downward toward the water source, promoting a robust root system. Since the top layer of soil remains drier, this method also reduces conditions favorable for pests like fungus gnats, which prefer moist surface soil for laying eggs.
The method also helps maintain the soil’s structure by preventing the compaction that occurs when water is forcefully poured onto the surface. Uncompacted soil retains better aeration, allowing oxygen to reach the roots for healthy cellular respiration. By only absorbing the water it can hold, the risk of waterlogged soil and subsequent root rot is significantly lowered.
Step-by-Step Instructions
To begin bottom watering, select a container large enough to hold the plant pot, such as a sink or deep saucer. Fill the container with a few inches of room-temperature water, ensuring the water level covers the bottom inch or two of the pot. If your tap water is heavily chlorinated, allowing it to sit for 24 hours or using filtered water may be beneficial for sensitive plants.
Place the potted plant directly into the water bath. The soaking time varies based on pot size and soil dryness, but typically ranges between 15 minutes and an hour. As the plant absorbs water, small air bubbles may rise to the surface, signaling that dry pockets in the soil are being filled.
Determine completion by touching the surface of the soil. Once the top layer feels uniformly moist, the soil has reached full saturation. Immediately remove the pot from the water bath to prevent over-saturation and potential root suffocation. Allow the excess water to drain completely before returning the plant to its location.
Specific Plants That Should Be Excluded
The convenience of bottom watering does not extend to all plant types, and universal application can cause problems for certain species. A major drawback is that the technique causes mineral salts from fertilizer and tap water to accumulate on the soil surface as water evaporates. This salt buildup can become toxic over time, leading to leaf burn and inhibiting water uptake. Therefore, all plants, even those regularly bottom-watered, require a thorough top-watering flush every four to six months.
Plants that prefer fast-draining, gritty soil mixes, such as most succulents and cacti, are poorly suited for this technique. These plants evolved to withstand long periods of drought, and their shallow root systems are highly susceptible to rot if exposed to prolonged moisture. Placing a succulent in a water bath contradicts its biological need to dry out completely between hydration cycles.
Extremely large plants in containers exceeding 8 to 10 inches in diameter are also impractical to bottom water effectively. The time required for capillary action to draw water from the bottom of a deep pot to the top surface can be excessively long. For these larger specimens, top watering until water drains from the bottom remains a more efficient method to ensure even saturation.