How does a self watering planter work? A self watering planter has a water reservoir under the potting mix. Water rises into the root zone by capillary action, the same way a sponge soaks up liquid, while an overflow hole stops the reservoir from flooding the roots. You refill through a fill tube instead of watering the surface, which keeps moisture steady.
Key takeaway: A self watering planter is ideal for vegetables, herbs and thirsty tropical houseplants. Use a light soilless mix, keep the reservoir from running dry, and avoid them for cacti and succulents that need to dry out.
| Part | Job |
|---|---|
| Reservoir | Stores water below the soil |
| Wicking column or wick | Carries water up into the mix by capillary action |
| Fill tube | Lets you refill without wetting the surface |
| Overflow hole | Sets the maximum water level so roots do not drown |
| Cover (optional) | Cuts evaporation and weeds, like mulch |
What Is a Self Watering Planter?
A self watering planter, also called a subirrigated or wicking container, is a pot with a built-in water reservoir in the bottom. Mississippi State University Extension explains that potting media pull water up from the reservoir by capillary action, creating consistent moisture in the root zone. You can buy them or build one from a storage tote or bucket.
University of Illinois Extension notes that self-watering pots draw water from the bottom through small soil columns, rope wicks or moisture sensors without making the soil too wet. They are especially useful for people who cannot check plants every day.
How Does Capillary Action Water Plants?
Capillary action lifts water through the tiny pores in potting mix. University of Kentucky Extension explains that the smaller the particles, the higher water can climb against gravity, and that in its wicking container design, capillary action moves water roughly 4 inches (10 cm) above the drain hole. Roots grow down into that moist zone and draw what they need.
This is the same principle behind a hydroponic wick system, except a self watering planter uses potting mix and usually plain water.
Which Plants Grow Best in a Self Watering Planter?
Plants that like steady moisture grow best in a self watering planter. Illinois Extension says consistent water is great for vegetables and tropical houseplants, and Mississippi State notes these containers also grow flowering ornamentals well. Thick-leaved cacti and succulents, which need to dry out, usually do not justify one.
| Plant group | Fit | Notes |
|---|---|---|
| Tomatoes, peppers, cucumbers | Excellent | Steady water helps reduce stress |
| Lettuce, kale, herbs | Excellent | Compact and thirsty |
| Peace lily, ferns, calathea | Very good | Like evenly moist soil |
| Snake plant, cacti, succulents | Poor | Prefer to dry between waterings |
What Potting Mix Should You Use in a Self Watering Planter?
Use a soilless potting mix in a self watering planter, never garden soil. Mississippi State Extension recommends mixes made of peat moss, pine bark, coir, vermiculite and perlite, and warns that native soil or bagged products meant for amending garden beds have the wrong porosity and water-holding capacity. Mixes with wetting agents wick water better.
The same publication says peat-based media can be reused for many years in these containers with a little new mix added each season. If you use peat, Mississippi State suggests mixing in 1 cup of dolomitic or calcitic lime per cubic foot of medium before planting.
How Do You Fertilize a Self Watering Planter?
Fertilize a self watering planter by banding granular fertilizer on top of the mix, not by adding liquid fertilizer to the reservoir. Mississippi State Extension warns that water-soluble fertilizer in the reservoir can raise soluble salts and burn roots. It suggests about 0.5 pound (approximately 1 cup) of 5-5-5, 8-8-8 or 10-10-10 per cubic foot of mix in a narrow band.
- Fill the planter with moistened soilless mix.
- Add lime if your mix is peat-based.
- Band granular fertilizer in a narrow strip on top; do not mix it in.
- Set plants beside, not on, the fertilizer band.
- Add a cover with holes for plants to reduce evaporation.
- Fill the reservoir until water runs from the overflow.
- Side-dress heavy feeders later; Mississippi State suggests 1 teaspoon of calcium nitrate through the fill tube for crops like tomatoes.
How Often Should You Fill a Self Watering Planter?
Fill a self watering planter often enough that the reservoir never runs dry. Mississippi State Extension says plants still use water as fast as in regular containers, and if the reservoir empties, capillary action stops. In hot weather with large plants, that can mean filling every day. Small houseplant pots may go a week or more.
Check the water level indicator or look down the fill tube. Water until it trickles from the overflow hole; the planter cannot be overwatered that way.
What Are the Pros and Cons of a Self Watering Planter?
| Pros | Cons |
|---|---|
| Steady moisture; less wilting | Costs more than a basic pot |
| Less evaporation and runoff (UK Extension) | Reservoir can breed mosquitoes if left open |
| Fewer weeds with a dry surface | Salts can build up without flushing |
| Great for travel and busy schedules | Poor fit for plants that need to dry out |
How Do You Build a DIY Self Watering Planter?
You can build a DIY self watering planter from two nested buckets or a storage tote. University of Kentucky Extension’s wicking container plan uses perforated pipe to create the reservoir, a PVC fill tube cut at an angle, and a drain hole that sets the water level. Fill the space above with porous mix that touches the water.
For a soil-free version, see our Kratky method guide, and for small spaces, our balcony hydroponics guide.
How Big Should a Self Watering Planter Be?
Choose a self watering planter sized for the mature plant, not the seedling. Larger planters hold more water and mix, so they buffer heat and need refilling less often. Shallow-rooted herbs and lettuce do well in small window-box styles, while tomatoes, peppers and cucumbers need deep, wide containers with large reservoirs.
| Crop | Practical planter size |
|---|---|
| Herbs, lettuce | 1–3 gallons (4–11 L) or window box |
| Peppers, eggplant | 5 gallons (19 L) |
| Tomatoes, cucumbers | 10+ gallons (38+ L) |
FAQs
Can a self watering planter cause root rot?
Rarely, if it has an overflow hole and a light mix. Heavy soil or a blocked overflow can drown roots.
Should I water from the top at first?
Yes. Water the mix from above at planting so wicking starts, then switch to the fill tube.
Do self watering planters work for orchids?
Most orchids prefer to dry slightly; use them only with very open bark mixes.
How do I stop mosquitoes?
Keep the fill tube capped and the reservoir covered.
Should I flush the mix?
Water heavily from the top a few times a season to wash out salts.
Sources
- Mississippi State University Extension — Subirrigated Containers for the Mississippi Gardener (P2971)
- University of Illinois Extension — Container Drainage Options
- University of Kentucky Extension — Wicking Containers: A Self-Watering Garden System (AEN-157)
- UMass Amherst — Subirrigation Systems
- Photo credits (Wikimedia Commons, edited with titles): 366 Highbush Blueberry – Vaccinium corymbosum, Leesylvania State Park, Woodbridge, Virginia by Judy Gallagher (CC BY 2.0); Tredegar House, The Orangery, Potted lemon tree – geograph.org.uk – 6890072 by Michael Garlick (CC BY-SA 2.0); Man turns drying chili peppers, Turkey by Rotadefterim (CC BY-SA 4.0); Peace lily – 2 by W.carter (CC BY-SA 4.0); White plastic bucket by Santeri Viinamäki (CC BY-SA 4.0)