Bottom watering, also known as sub-irrigation, is a method of watering plants where the water is delivered directly to the soil and roots rather than from the top down. This technique has become increasingly popular among houseplant enthusiasts and gardeners due to its efficiency and effectiveness.
What is Bottom Watering?
With bottom watering, the plant’s container is placed in a receptacle like a tray, bowl, or basin that contains some water. The water is then absorbed upwards through the drainage holes at the bottom of the pot by capillary action, where it delivers moisture directly to the roots.
This is different from top-down watering where water is poured or sprayed from above onto the topsoil and allowed to filter downwards to the roots. With bottom watering, only the lower portion of the soil gets wet initially, and the moisture moves upwards as needed over time.
How Long Does Bottom Watering Take?
The amount of time it takes to bottom water plants effectively can vary based on several factors:
- The size of the plant’s container – Larger pots and planters will require more time to absorb water from the bottom up.
- Soil composition – Soils with high percentages of peat, coco coir, vermiculite, perlite or bark tend to absorb water faster than dense clay-like soils.
- Water temperature – Warm water is absorbed more quickly than cold water.
- Water level in receptacle – The lower the level of water in the tray or basin, the longer it takes for uptake.
- Type of plant – Some plant species and varieties take up water faster than others.
- Time since last watering – Dryer soils will absorb water faster than damp ones.
Taking these factors into account, the average time range for bottom watering houseplants and container gardens is:
| Container Size | Minimum Time | Maximum Time |
|---|---|---|
| 2-4 inches | 10 minutes | 20 minutes |
| 4-6 inches | 20 minutes | 30 minutes |
| 6-8 inches | 30 minutes | 45 minutes |
| 8-10 inches | 45 minutes | 60 minutes |
| 10-12 inches | 60 minutes | 90 minutes |
For smaller pots and containers up to about 6 inches, 15-30 minutes is usually sufficient. For larger containers, plan on bottom watering for 30-60 minutes to ensure the soil is thoroughly saturated.
Tips for Effective Bottom Watering
Follow these tips for the best results when bottom watering your houseplants and garden containers:
- Always water in a sink, tub, basin or tray – Don’t leave plants sitting directly in water for extended periods
- Remove excess water from receptacle after watering so plants aren’t left standing in water
- Add water again if it drops below bottom of pot before time is up
- For fastest absorption, use warm water between 70-80°F
- Water when top 1-2 inches of soil are dry
- Allow medium to almost completely dry out between waterings
- Ensure container has drainage holes so excess water can escape
Benefits of Bottom Watering
Compared to traditional top watering methods, bottom watering offers a number of advantages:
- Prevents Diseases – Minimizes risk of fungal and bacterial diseases by keeping foliage dry
- Saves Water – Less run off and evaporation compared to top watering
- Avoids Root Shock – Gentle, even saturation encourages stronger root growth
- Reduces Mineral Buildup – Salts and minerals get flushed out drainage holes rather than accumulating on soil surface
- Good for Vacations – Don’t have to worry about hired help overwatering while away
- Less Labor Intensive – Don’t have to water each plant individually from the top
Potential Drawbacks of Bottom Watering
While generally very effective, there are a few potential downsides to bottom watering that should be kept in mind:
- Overwatering can still occur if left soaking for too long
- Some fertilizers need to be watered in from the top
- Not practical for outdoor gardens and larger in-ground plantings
- Requires a water receptacle like a tray for each pot
- May need to top water occasionally to rinse built up salts from leaves
How to Tell When Bottom Watered Plants Need Water Again
Determining when to water again after bottom watering depends on the factors discussed earlier like container size, plant type, and soil composition. Here are some general guidelines for when to resume bottom watering:
- For small containers under 4 inches, check soil every 2-4 days and water when top 1 inch is dry.
- For 4-6 inch pots, check every 5-7 days and water when top 1-2 inches are dry.
- For larger planters 6 inches or greater, check soil every 7-10 days before watering again.
- Lift pot to check weight – light means it’s time to water.
- Observe plant leaves – wilting, drooping, or dull color indicates need for water.
- Use a moisture probe to check lower soil – should be slightly damp but not wet.
Common Problems to Avoid with Bottom Watering
While bottom watering offers many advantages, it can also lead to issues if not done properly. Here are some common bottom watering mistakes to avoid:
- Sitting plants in water too long – Extended exposure to wet soil leads to root rot.
- Allowing pots to float in receptacle – Makes it hard for roots to access water.
- Failure to empty tray or basin – Stagnant water breeds bacteria and mosquitoes.
- Watering too frequently – Doesn’t allow soil to dry out adequately between waterings.
- Using cold water – Slows absorption and stresses plant roots.
- Bottom watering outdoor containers – Risks breeding mosquitoes in standing water.
How Bottom Watering Works
When the bottom portion of a container is placed into water, the moisture is drawn up into the potting mix through a process called capillary action. Here’s a look at the science behind bottom watering:
- Capillary action occurs due to adhesion and cohesion properties of water molecules.
- Water molecules stick to (adhere) to soil particles and “pull” other water molecules along (cohesion).
- This creates a continuous flow of water molecules bonding and moving through the spaces in the soil.
- The narrower the spaces, the higher the water can flow upwards against gravity.
- Water moves from wetter areas to drier areas until moisture level equalizes.
As the plant receives water, its roots absorb what’s needed. Air still fills pockets not occupied by water, providing good oxygenation.
How to Start Bottom Watering
Shifting to a bottom watering regimen is easy with a little preparation:
- Get a watering receptacle – Try a tray, bowl, dish tub, etc. Plastic or ceramic both work.
- Filled receptacle with water – Use room temperature or warm water for fastest absorption.
- Place plant container in receptacle – Water level should come up 1-2 inches on pot.
- Let soak for appropriate time – See table earlier for general guidelines.
- Remove from water and empty excess – Don’t leave plant standing in water.
- Resume normal routine – Bottom water every 1-2 weeks as needed.
Making the switch from top watering does not usually shock plants. But monitor closely at first in case any issues arise.
How to Bottom Water Specific Plants
While technique remains essentially the same, watering duration and frequency should be adjusted to suit the needs of specific plants. Here are some bottom watering guidelines for popular houseplants:
Succulents and Cacti
- Use fast draining cactus/succulent soil mix
- Soak for 10-20 minutes as needed every 2-3 weeks
- Allow soil to fully dry between waterings
Pothos
- Use all purpose or indoor potting mix
- Soak for 20-30 minutes every 1-2 weeks
- Water when top inch of soil is dry
Peace Lily
- Use all purpose or indoor potting soil
- Soak for 30-45 minutes when top 2 inches are dry
- Keep soil moderately moist, water every 1-2 weeks
Chinese Evergreen
- Use indoor potting mix amended with perlite/vermiculite
- Soak for 45-60 minutes every 2-3 weeks
- Allow top 50% of soil to dry out before watering again
Snake Plant
- Use cactus/succulent mix or amend soil with perlite
- Soak for 20-30 minutes every 3-4 weeks
- Allow soil to fully dry between waterings
Philodendron
- Use indoor potting mix amended with peat moss
- Soak for 30-45 minutes when top 2 inches are dry
- Keep soil moderately moist, water every 10-14 days
Bottom Watering Outdoor Containers
Bottom watering can also be used for patio planters, pots and hanging baskets outdoors. Follow these tips:
- Avoid leaving standing water to prevent mosquito breeding
- Lift containers to saturate soil and then let drain thoroughly
- Empty excess water from saucers/trays after watering
- Supplement with occasional top watering to rinse foliage
- Adjust method and increase frequency during hot, dry weather
Bottom Watering Indoor Plants with Lechuza PON
An easy way to bottom water houseplants is using a Lechuza sub-irrigation system. This consists of:
- Plastic planter pot (with water level indicator)
- Water reservoir base/legs it sits inside
- Watering spikes that connect pot to base
To use, simply fill reservoir base with water once a month. Absorbent spikes pass moisture into the soil via capillary action as needed, providing up to 6 weeks of water to plant roots.
How Bottom Watering Benefits Plants
Bottom watering provides a number of beneficial effects for plant health and growth:
- Encourages extensive root growth and proliferation
- Keeps root zone cooler and better oxygenated
- Allows establishment of healthy populations of soil microbes
- Sustains more consistent moisture levels in soil
- Reduces plant stress and risk of disease
- Minimizes chances of overwatering or underwatering
- Provides gentle hydration analogous to natural rainfall
Ideal Plants for Bottom Watering
While suitable for most plants, some species are especially well-suited to bottom watering care:
- Succulents and cacti
- Bromeliads
- Orchids
- Ferns
- Bonsai trees
- Herbs like basil, oregano, thyme
- Vegetables grown in containers
- African violets
- Spider plants
- Calatheas
In general, plants that enjoy evenly moist (but not wet) soil do very well with sub-irrigation watering methods.
Conclusion
Bottom watering is an efficient, low-effort way to hydrate container plants that provides moisture directly to the roots. While drainage and other factors affect timing, most pots will saturate within 30-60 minutes. Pay close attention to your plants’ needs and environmental conditions when sub-irrigating. Mastering this technique provides improved plant health, stronger roots, and easier maintenance for indoor and outdoor container gardening.
