Bottom watering (sub-irrigation) means standing a container in a shallow tray of water or nutrient solution and letting it soak up through the drainage holes. Water moves upward by capillarity until the medium is moist, and the excess is then removed. Ebb-and-flow tables automate the same process.
In practice
It wets dry peat and coco that repel water from above, keeps the surface drier (which discourages fungus gnats), and avoids splashing. Leave the pot in the tray for about 15-30 minutes, then empty what remains; leaving a pot standing in water for hours waterlogs the base. Because water moves only upward and does not drain through, salts build up near the surface over time, so top-water to runoff now and then to clear them.
Commercial nurseries use sub-irrigation widely for potted plants.
Don't confuse with
Runoff is the water or nutrient solution that drains out of the bottom of a container after irrigation; growers test it to see what is happening in the root zone.Ebb and flow (flood and drain) periodically floods a tray of potted plants with nutrient solution, then drains it back to a reservoir, pulling fresh air into the medium.Peat is partially decomposed sphagnum moss from bogs, the base of most potting mixes; it holds water and nutrients well but is acidic and needs lime.Coco coir is a growing medium made from processed coconut husk, prized for holding water and air at once; it binds calcium and magnesium unless buffered.Small dark flies of the genus Bradysia (family Sciaridae) whose larvae live in wet growing media, feeding on fungi, organic matter and young roots.A wick system is a passive watering method in which an absorbent cord draws water or nutrient solution up from a reservoir into the medium by capillary action.A recirculating (closed) system returns drained nutrient solution to the reservoir to be reused, saving water and nutrients but needing more monitoring and sanitation.Overwatering is watering so often that the medium stays saturated, starving roots of oxygen, which causes drooping, slow growth and root disease.Ceramic sensor watering uses a porous ceramic cone in the medium that opens a small valve when the soil dries, feeding water from a gravity-fed reservoir on demand.
