Soaking plants in water, often called bottom watering, is a technique used to rehydrate potting mix that has become extremely dry or water-repellent. Many commercial soil blends contain peat moss or coir, which are excellent for retaining moisture but can become hydrophobic—meaning they actively repel water—when they dry out completely. When soil is hydrophobic, water poured over the top runs down the sides and out the drainage holes, leaving the root mass dry. Soaking the container from the bottom uses capillary action to draw water up into the soil, ensuring the entire root zone is uniformly rehydrated.
Identifying When Soaking is Necessary
A plant needs soaking when its soil is so dry that it can no longer absorb water efficiently from the top. The most reliable indicator is the “light pot” test, where an extremely dry pot feels noticeably lighter than a recently watered one. Water immediately running through the drainage holes without the soil surface becoming damp is another clear sign of hydrophobic soil.
When soil is hydrophobic, water bypasses the root ball, running between the dry soil and the pot wall. You might also notice the soil surface pulling away from the interior edge of the pot, creating a gap that allows top-watered moisture to escape. These signs indicate the soil is too dry for the plant to access moisture, requiring a thorough bottom soak to break the water-repellent barrier.
Standard Soaking Durations for Potted Plants
For a typical houseplant in a standard commercial potting mix, the soaking duration ranges from 15 to 45 minutes. The pot should be placed in a basin filled with water covering about one-half to three-quarters of the pot’s height. The water moves upward through the soil via capillary action, gradually rehydrating the entire root mass.
The most accurate way to know when the soak is complete is by observing the soil surface. When the top layer of the potting mix becomes visibly moist and darkens, the water has wicked all the way through the soil. The plant should then be removed from the water to prevent overly saturated conditions. Soaking for periods longer than one to two hours is ill-advised, as it can lead to anaerobic conditions where oxygen is pushed out, potentially causing root rot.
Duration Adjustments Based on Plant Type and Media
The ideal soaking time requires adjustment based on the potting media composition and the plant’s sensitivity to moisture. Plants potted in fast-draining, chunky substrates, such as bark-heavy orchid mixes, may require a longer soak, sometimes up to an hour or more, to fully saturate the larger particles. Conversely, dense, clay-heavy soils, while slow to absorb water initially, may also benefit from a longer saturation time to ensure the tight structure is completely moistened.
Succulents and cacti are water-sensitive plants that benefit from bottom watering but need a shorter duration due to their susceptibility to overwatering. For these arid-adapted plants, a soak of 5 to 15 minutes is sufficient, or until the topsoil is just barely moist. The “soak and dry” method for succulents mandates that the soil dries out completely within a few days to prevent root rot.
Soaking Materials Before Planting or Repotting
Soaking is a necessary preparation step for certain materials before they are used in potting. Compressed coco coir bricks, a popular peat moss alternative, must be hydrated before use by soaking them in water for 15 to 30 minutes. This process allows the highly compressed material to fully expand, typically increasing its volume by four to seven times.
New terracotta pots are highly porous and should be soaked in water for at least 30 minutes, or ideally overnight, before planting. If a dry terracotta pot is used, its porous clay walls will immediately wick moisture away from the newly added soil and plant roots. Pre-soaking saturates the clay, preventing it from drawing water from the soil and stressing the young plant during the initial watering phase.