Watering containers: how often, how much and self-watering pots

At a glance

How often: it depends on the pot and the weather

None of these sources gives a fixed schedule. University of Maryland Extension says watering needs depend on plant type, plant size, container size, sun or shade and soil volume, and that plants need more water as they get larger and temperatures rise. Illinois Extension adds the time of year and the container's location, and says to water each plant by its needs, not by a general rule of thumb. The published ranges:

What makes a pot dry faster

• Small size. Small pots dry out faster than large ones (Clemson, Arizona); larger pots hold moisture longer (Kansas State). Penn State singles out pots under 10 inches across and says raised beds less than 18 inches deep should be watered like small containers. Minimum sizes by crop are in container sizes for vegetables.
• Porous walls. Clay and other porous pots lose water through their sides (Clemson); plastic does not dry out as quickly as terracotta (Penn State). For fabric, see grow bags.
• Hot surfaces. Containers can dry out very quickly on a concrete patio in full sun (Clemson).
• No rain. Pots next to a house, building or porch get no natural rainfall (UMD).
• Wind. Balcony plants in full sun or wind dry out quickly (MGNV); see balcony gardening.

Checking before you water

UMD and Kansas State both say to water only when the mix feels dry. Penn State warns that soil can look damp when it is not, so feel rather than look. The checks the sources describe:

How to water, step by step

1. Check first. Press a finger into the mix; if it is dry, water; if not, wait until it feels dry (UMD).
2. Aim at the base of the plant. Keeping water off the leaves helps prevent foliar disease (UMD, Illinois).
3. Water until it drains. Keep going until water runs out of the drainage holes (Iowa State, UMD, Clemson, Penn State, Kansas State, MGNV). One long application is far more effective than several shallow ones (UMD). A breaker nozzle on a hose or watering can spreads the water evenly (Kansas State).
4. Watch for run-through. Mix that has dried out completely shrinks from the sides, so water runs down the gap and out the bottom while the root ball stays dry (Iowa State, Illinois); a follow-up watering is often needed (Illinois). To rewet it, Iowa State sets the pot in a tub of water for 20 to 30 minutes; UMD soaks it halfway until the surface is moist.
5. Empty the saucer. UMD empties saucers after watering or rain, and Minnesota warns against trays that keep the mix waterlogged. MGNV discards saucer water after a few minutes to keep salt from building up and to discourage mosquito larvae. Pot feet raise containers for better drainage (UMD).
6. Keep to a time. Watering early in the morning leaves water available for the hottest part of the day (Illinois); Kansas State's simplest method is hand watering every morning. Penn State waters at about the same time each day, since irregular timing can leave a plant facing two days of sun and heat on one watering. If plants have wilted by evening, water them right away rather than waiting for morning (Illinois).

Too dry, too wet

Both extremes do harm. Letting containers dry out completely between waterings leads to flower and fruit drop, and severe wilting hurts plant quality and health (Illinois). In tomatoes, NMSU's Southwest Yard & Garden ties blossom end rot to wilting: on days when plants wilt, there is often too little water to carry calcium to the young fruit. At the other end, too much water, watering too often and too little drainage are the leading causes of overwatering, which can lead to root rot (UMD). Waterlogged mix leaves roots short of oxygen (Illinois), and in cool weather containers kept too wet may develop root rots (Clemson). Minnesota sums it up: most container plants prefer moist, not soggy, soil.

Ways to water less often

• Bigger pots. For container tomatoes that were watered every morning but completely dry by evening, NMSU suggests a larger container with more soil, which gives a greater water reserve.
• Mulch. Mulch reduces evaporation and moderates soil temperature (Minnesota). Its suggestions are herbicide-free grass clippings, burlap, straw or hay for large containers, and shredded newspaper or coconut coir, while noting mulch may not suit every container. Clemson says mulching and windbreaks can reduce containers' water needs.
• Keep the pot cool. NMSU suggests light-colored pots or shading the pot to cut soil heating and evaporation, and a spot that is sunny in the morning and shady in the afternoon. Clemson groups containers so their foliage shades the soil.
• Plastic rather than porous pots. Plastic does not dry out as quickly as terracotta (Penn State).
• Water-holding gels. Many potting mixes contain gels that absorb water and release it as the mix dries (Illinois); they do not remove the need for timely watering (Illinois Extension's watering page).
• Drip on a timer. Kansas State recommends a small drip system on a timer for consistent moisture, and Clemson suggests automatic drip emitters for gardeners who are away a lot. Parts, emitter sizes and run-time math are in drip irrigation for containers.

Self-watering containers

A self-watering container has a water reservoir in its base and an overflow hole in one side instead of drainage holes in the bottom (UMD). The mix sits on a perforated platform or false bottom above the reservoir, and water moves up into it by capillary action (UMD, Kentucky); in Illinois Extension's version, soil in a small basket set into the reservoir acts as the wick. Water goes in through a fill tube, and once the reservoir is full the excess leaves through the overflow hole (Kentucky).

Advantages. Water is always available in the reservoir, bottom watering cuts surface evaporation and runoff, the drier surface means fewer weeds, and the reservoir captures rain (Kentucky). UMD adds that they conserve water and nutrients and that plants can go a few days without attention; Illinois calls them a low-maintenance option for gardeners who are short on time or space or have poor soil.

Drawbacks. They cost more to build than traditional beds, may freeze sooner in fall, and several plants in one container may need more frequent watering and feeding (Kentucky). Commercial models can be expensive (Illinois). Kentucky also advises against overfilling when rain is on the way.

Watering, fertilizer and salts

Frequent watering washes nutrients out of containers (Iowa State, Minnesota, UMD). UMD advises regular feeding, light feeding every two weeks for long-season crops, following the product label; Penn State adds slow-release fertilizer at planting and soluble fertilizer every two to four weeks. Every watering with tap water adds salt to the mix, so Arizona Extension flushes accumulated salts with periodic large applications of water that drain away quickly. Arizona and Illinois both advise against softened water.

Summer watering checklist

• Each container has a drainage hole (UW–Madison), or an overflow hole if it is self-watering (UMD).
• Pots checked at least once a day, twice on hot, dry or windy days (Clemson).
• Finger test before watering: dry 1–2 inches down means water (Iowa State).
• Water at the base until it runs from the drainage holes.
• Saucers emptied after watering and after rain.
• Pots under eaves or a porch watered even after rain.
• Large containers mulched; pots grouped or shaded on a hot patio.
• Self-watering reservoirs topped up through the fill tube.
• Feeding kept on schedule, since watering leaches nutrients.
• For time away: drip on a timer or a self-watering container.

Crop-specific watering is on the crop pages, for example growing tomatoes in containers.

Where sources differ