There are two common ways to water houseplants – from the top and from the bottom. The debate about which one is best has been raging for many years and it’s time to put a stop to the debate and decide once and for all, which is best – top watering or bottom watering?
Top Watering vs Bottom Watering
What are these two methods? When I asked people in our Facebook Group for the pros and cons it became clear that not everyone understands how these methods should be done. Lots of people seem to do a partial bottom watering, or a partial top watering. That can work, but it can also lead to problems. For that reason partial watering methods are not considered in this discussion.
When top watering, you pour water into the top of the pot until a) water runs out the bottom and b) the soil is fully saturated. It does not mean you have to pour water on the plant – you water the soil.
For this technique you set the pot into a reservoir that holds enough water to fully saturate the soil and many people use the kitchen sink for this. It is important that water soaks right up to the top of the soil layer to ensure that the top roots are watered.
Removing Excess Water
Any excess water sitting in a tray below the pot is removed in both methods.
Infrequent watering can lead to soil that is very dry and which pulls away from the side of the pot. It is then difficult to rewet. This is more of a problem with top watering because the added water just runs down the space between the inside of the pot and the soil, leaving the root ball dry. Watering from below is less likely to have this problem provided that enough water is used.
This is not a problem when plants are watered on time. Even if it does happen, it is easily solved by sitting the pot in water or by slowly pouring excess water from above.
Soil That is Too Wet
Some people claim that top watering makes the surface of the soil wet which can lead to crown rot. If you water properly, the top of the soil will be equally wet using either technique. Crown rot is caused by too much water, high humidity and not enough ventilation. In special cases, like some orchids, watering on top of the plant can cause water to sit in leaf axils where it can cause rot, but watering from the top can be done without any water getting on the plant. Top watering does not cause rot. Pouring water onto plants may.
The soil will be equally wet using either watering method. If the plant needs a drier environment, water less often or change the soil so it is more porous.
Water Spots on the Leaves
It is claimed that watering from above will leave water spots on the leaves. That is true if you don’t water carefully. Use a watering can with a smaller spout and keep it closer to the soil to eliminate this problem.
Others claim that getting water on certain leaves like African violets and Streptocarpus cause rotting on leaves, but that is not true. I’ve tested streptocarpus by putting water on the same leaf every day for two weeks and the leaf showed no signs of rot. It is also not true that some plants are “sensitive to splashed water”. What do you think happens in nature when it rains? I think this myth has been perpetuated by gardeners who water too frequently.
I have seen a number of other claims for bottom watering that are not valid.
- Leads to deeper roots – that is only true if you don’t water properly from above.
- Has fewer fungus gnats because the surface of the soil stays drier – that is only true if you don’t water properly from the bottom.
- Saturates the root ball more evenly – not true – when both methods are done correctly, they both saturate the root ball.
Accumulation of Mineral Salts
One of the reason watering from above is recommended, especially when hard water is being used, is that the water flushes out excess minerals and fertilizer (salts). The exact opposite happens with bottom watering. Water soaks up the pot bringing salts to the soil surface. As the water evaporates from the top of the soil, salts precipitate and accumulate there. This can prevent roots from growing in the top layer of soil. If such a pot is now watered from above, the water dissolves some of the salts and a concentrated solution of salts moves down into the lower root zone, which can cause significant damage.
One site suggested that you, “flush the soil (from above) after bottom watering to get rid of the excess salts”. But if you do that you might as well water from above!
Salt buildup is the main argument against bottom watering.
It is Easier!
I see numerous claims that say bottom watering is easier and saves time. This depends very much on your setup and the number of plants you have.
Moving a lot of plants to a kitchen sink and waiting for the water to soak up the pot is not exactly a fast process. Watering a lot of plants overhead is a lot easier especially if they are sitting in containers with false bottoms so pots don’t sit in water.
Some people use wick watering which is a form of bottom watering and it can be faster since you water less often, but then you do have to set up all your pots with wicks and bottom reservoirs.
Either watering method can be faster if you are set up for it.
What Do Commercial Greenhouses Do?
There are thousands of commercial greenhouses that use bottom watering and thousands more that use top watering. Clearly both systems work and produce good plants. The key is that they thoroughly wet the root system.
Are African Violets Different?
The subject of watering African violets comes up a lot in this debate. A lot of people claiming that African violets are “special”. They need to be watered different than other plants because they can’t have water poured on them.
So, I decided to ask an expert. I contacted HoltKamp Greenhouses, the producer of Optimara violets. Those are the African violets you see everywhere and they are “Earth’s largest grower of African Violets”. I asked them if they use top or bottom watering. I got a reply directly from their Vice President, Reinhold Holtkamp and he said,
“In our greenhouses we use temperate water and overhead water our plants with water that is adjusted to the same room temperature. Once they start to flower we water from the bottom. All our tables have a capillary mat that will allow for water to be more evenly distributed. “
He goes on to say, “Most African Violets die because of overwatering. Many plants are potted into a peat moss blend that has wetting agents and that cause the plants to stay moist to long. If not properly monitored, it is easy to allow the plants to get water locked and the lack of oxygen getting to the roots will cause them to develop a fungus called Phytophthora. You can see a lot more information on https://myviolet.com/easy-care or the self diagnostic tool on Optimara.com Dr. Optimara: Symptom-Based Guide for Diagnosing African Violets“.
Clearly African Violets can be watered from above or below. Using the right soil and watering frequency are the keys to healthy plants.
Which Method is Best – Top or Bottom Watering?
Both methods work when done correctly. Gardeners with hard water should probably use top watering, but bottom watering will work provided you watch the salts. When they accumulate, they can easily be scraped off the top of the soil.
Top watering does not lead to disease if done correctly. Gardeners using this method need to be aware of the fact that soilless mixes can become too dry to wet easily. Prevent his by watering on time and if it does happen, just soak the root ball for half an hour in water.
Both methods saturate the soil and provide equal watering.
Tips and Tricks for Watering Plants
Here are some more posts about watering plants.