While watering is one of the more common tasks we do when caring for plants, it’s often one of the most misunderstood. If you are a ‘plant person’ and friends or relatives ask ‘How often should I water (insert name) plant?’, it’s a difficult question to answer in a couple of words given all the variables.
There are a number of different ways to determine when to water that will be outlined in this article. One thing to keep in mind is that while we may want to water a lot at a given time so we don’t have to water again very soon, that may not be what is best for the plants. It’s not good for plants to constantly remain wet. They benefit from drying out some and allowing oxygen to be prevalent in the root zone.
Plant Indicators of Water Stress:
Wilting
A common assumption is that a wilting plant needs to be watered (Figure 1). While that is usually true, overwatered plants will often wilt as well. Ironically, one of the reasons why overwatered plants die, is due to a lack of water. When plants have a consistently saturated rootzone, their roots become compromised and can no longer uptake water. So, in essence overwatered plants will also wilt and can perish from a lack of water in the plant as well.
Dull, Greenish-Gray Color
The color of a plant can also give subtle clues on whether or not it needs watering. For individual plants, this can be a challenging method to use, but if you are growing a number of the same plant, often plants that are starting to go into water stress will have a duller grayish cast to the foliage (Figure 2). A lot of the time, the plants on the edge of a group of plants will dry out more quickly, and only those plants may need to be watered. This is also a method to identify pots that you may have missed watering.
Bronze or Purple Foliage
A popular gardening practice is to mix different species of plants in containers. This can create an attractive presentation, but keep in mind it’s best to mix plants that have similar water needs. If one species of plant needs more water than the others in the container, watering can be challenging. In some situations, some species of plants under perpetual water stress can develop purple or bronze foliage (Figure 3).
Potting Media Indicators for Water Status
Potting media can be used as a good indicator as well. The color and other traits can be used as an indicator of moisture status for peat-based potting mixes, but caution needs to be made when using color as an indicator for other rooting substrates.
Levels have been developed as a useful tool to describe the water status of potting media (Table 1). This was developed on a scale of 1-5, with 1 being the driest and 5 being the wettest.
| Potting Media Moisture Levels | |||||
|---|---|---|---|---|---|
| Parameter | 1: Dry | 2: Medium Dry | 3: Medium | 4: Medium Wet | 5: Saturated |
| Color | Tan/gray | Light brown | Brown | Dark brown | Black, shiny |
| Water | No water when squeezed | No drips when squeezed, squeaks | A drop when squeezed | Drips when squeezed | Freely drips without squeezing |
| Structure | Dusty, will not from a ball, | Barely sticks or forms a ball that crumbles | Soft ball that cracks apart | Easily forms a ball that sticks together | Forms a loose ball, semi liquid |
We rarely want to have our plants in Level 5, which is saturation, or Level 1, at which there is no water available in the media (Figure 4). If we water to Level 5, it takes much longer for the media to dry out, and saturated media limits plant functions due to a lack of oxygen near the roots.
Some generalities exist, but they will not hold true for all plants. When starting seeds, we generally start out at a Level 4 but only let them dry down to a Level 3 early on. If you are sowing pelleted seed or plants with high water needs like a petunia, you may need water to Level 5 early on. Once we have true leaves on the seedlings, we typically water to a 4 and let them dry down to a 2. This is true for mature plants as well.
Other Factors to Ensure Watering Success
Consistent Filling of Containers
Uneven filling of containers can also create issues with watering. In Figure 5, the top left container was underfilled compared with the container in the bottom right. This means that the top left cell will have less potting media to hold water and will dry out more quickly.
Keeping Containers Level
Ensuring your containers are level will also assist in keeping consistent water status. Some benches are not level, or sometimes there can be items under the containers that prevent them from sitting level (Figure 6). Containers that are not level will not have a large reservoir for watering as it is applied, and more water will run off before it has a chance to soak in.
Sorting Plants by Size
From time to time some plants will grow at different rates than others. Several factors can contribute to variable growth rates, but once this occurs, it’s important to sort plants to make watering easier. If small plants are right next to large plants, it makes watering each plant to its ideal moisture level impractical. By grouping like plants together, watering can be done more evenly and individualistically (Figure 7). Watch a video demonstrating how to group plants by size.
Considering Container Size
The taller the container, the less likely the color at the top of the media is a good indicator if the plant needs to be watered, since there is more moisture in the bottom of the container than the top. In Figure 8 the view on the top is fairly dry and likely at moisture Level 2. Unpotting the plant shows there is still some moisture towards the bottom of the container. This plant is at the opportune time to water.
Checking Container Weight
Weight can be a very subjective way to determine if plants need to be watered, since as plants grow, they weigh more. But lifting plants before and after you water them gives you a sense of how heavy they are when they need to be watered. That way, when you notice plants are lighter, that can be an added indication of how much water is needed. This is especially helpful for indoor blooming plants that are placed in plastic sleeves which make it more difficult to look at the potting media.
Conclusion
There are many ways to determine when to water containerized plants. There is no one best way, but using several of the methods outlined above can help give an indication of when plants should be watered. Keep in mind that it can be good for plants to dry down, but not too much. If they are kept perpetually wet or excessively dry, that can inhibit growth and have adverse impacts on plant health. Successful watering comes from using a combination of these techniques to accurately determine when and how much to water, leading to more effective and consistent watering practices.
Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Yard and Garden, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on April 4, 2025. The information contained within may not be the most current and accurate depending on when it is accessed.