Some people like to water their orchids from the bottom, also known as “soaking”, instead of pouring water from above. This watering method can be quite convenient for indoor orchids and can save up on water. However, other people are strongly against soaking, saying it would increase the risk of root rot.
Whether soaking is good for your orchid depends on a combination of factors, including the type of growing medium, the orchid species, humidity, how dehydrated the orchid is, and how deep it is soaked.
In any case, you should not soak an orchid for over 30 minutes, let alone overnight, as it would do more harm than good, even though it would not kill it immediately.
In this article, we hope to put an end to this controversial topic among orchid growers by taking an in-depth look at when you should or should not soak your orchid, how long you should soak it, and how to do so properly.
1. Shallow vs. deep soaking orchids
When people talk about soaking their epiphytic orchids*, they can be talking about two very different ways of soaking.
(*Note: Since most of the orchids we grow at home are epiphytic (as opposed to terrestrial orchids that grow on the ground in soil), we will only talk about epiphytic orchids in this article.)
For many people, soaking an orchid means putting the pot on a deep tray with only an inch or a couple of inches of water. This is actually a semi-hydroponics setup or a self-watering system with a reservoir at the bottom permanently filled with water. This is also similar to putting a humidity tray with water and clay balls or rocks under a pot to increase the humidity around the plant.
Such a system would not damage the plant because there is no prolonged immersion of roots in water. This is in fact an efficient automatic watering system as the water at the bottom can wick upwards to where the roots are, keeping them constantly moist (not waterlogged) as long as there is water in the reservoir.
But for others, soaking means a deep soak, dunking, or submerging the whole pot or the entire root system in water. It is this deep type of soaking that is controversial and we shall discuss this in the next part.
2. Should you submerge orchid roots in water?
2.1 Potting medium
Whether you should submerge your orchids in water depends on the water absorption capacity of the growing substrate.
Soaking can be good for orchids that are grown in less water absorbent substrates to ensure that enough water is absorbed. These substrates are generally inert and are resistant to physical breakdown despite repeated soaking.
Such types of substrate include small pumice, which according to an experiment can only absorb 56% of its dry weight of water. Others include medium pumice (58%), large pumice (40%), large bark (38%). Substrates with an even lower water absorption capacity include LECA (28%), Kyodama (22%), medium pumice (Lava-lite) (22%), Lava rocks (16%).
Apart from water absorption capacity, you may also want to be careful with submerging light-weighted media such as bark, LECA, perlite, etc. in water as they will float out of the pot.
However, submerging the pot in water should be avoided when the potting medium has a high water absorption capacity. This is because a substrate that retains too much water can close off the air pockets inside the medium, suffocating the orchid roots and resulting in a higher chance with root rot.
For example, sphagnum moss can absorb 2120% or 21 times its own dry weight of water and Synthic (or synthetic sphagnum moss) can absorb 1368% or around 14 times its own dry weight of water. Other highly absorbent substrates include perlite (225%), small bark (96%), medium bark (88%) and Seramis (72%).
Also, prolonged contact with water can accelerate the physical decomposition of moss and small bark substrates, which can become too acidic for the orchid roots.
But, this is not to say that orchids potted in moss or other water-retentive media should not be soaked. Other factors such as the humidity of the growing environment, orchid species, etc. should also be taken into consideration.
2.2 Humidity of growing environment
Another factor to consider whether to soak your orchid or not is the humidity around the plant.
If you live in places with high humidity, e.g. above 70%, the orchids should not be watered by soaking, but by pouring water from above for 15-30 seconds.
On the other hand, if you live in dry climates with humidity below 70%, soaking for 10 minutes is actually good for the orchid. Soaking for 10 minutes is also good for mounted orchids since they do not have a pot to retain moisture.
2.3 Orchid species
Different orchid species also respond to soaking differently.
For some orchids, soaking their roots for too long can result in problems. For example, Cattleya alliance species (i.e. Cattleya, Laelia, Epidendrum, Encyclia, etc.) cannot tolerate soaking of more than 12 hours. Dendrobiums tolerate even less soaking of not more than 3 hours.
However, Tolumnias seem to do better when soaked overnight on a regular basis. Vanda roots can also be soaked for 24 hours without any problems on warm days.
2.4 How dehydrated is the orchid
Soaking also benefits highly dehydrated orchids with wrinkled and limp leaves to open up the pores.
You can submerge the roots in water, but not for more than 30 minutes.
An alternative is to water more frequently instead of soaking it for a long time.
3. How long should you soak orchids?
Soaking is not bad or in fact even beneficial if you do it moderately, ranging from a couple of minutes to 30 minutes, with respect to the aforementioned growing conditions of your orchid. In any case, do not submerge the orchid in water for more than 30 minutes.
If you soak only a couple of inches at the bottom of the pot, then you can keep water at the bottom for as long as you want.
Soaking orchids for more than 30 mins, or even overnight, is actually redundant. This is because orchid roots have a special covering called velamen that can absorb water very quickly within a minute into the vascular tissues.
Since an orchid can only absorb a certain amount of water at a time, giving them more water after it has enough will not make it more hydrated.
If by accident you have left an orchid soaking overnight, that would not cause immediate harm to your orchid. But, that could accelerate a breakdown of the potting medium if it is less resistant to breakdown, such as moss and small-sized bark.
4. How to soak multiple orchids?
If you have more than one orchid, you should not soak more than one plant in the same bath to prevent passing pathogens and fungal issues from one to another.
To do so, before soaking another orchid, the water needs to be changed and the bucket or sink needs to be sterilized with bleach.
This can result in using much water wastage if the water bath is big. The best solution for home growers is to soak each orchid in its cache pot to prevent sharing the same water bath. Cache pots also make a great self-watering system for your orchids while you are away from home.
5. Cache pot recomendations
Below are some great cache pot suggestions:
To sum up, submerging the entire roots of an orchid in water can be beneficial and a convenient watering setup for home growers if you do it moderately, ranging from a couple of minutes to a maximum of 30 minutes, depending on the potting media, orchid species, humidity in the environment, and how dehydrated the orchid is.
Soaking should be done properly by not sharing the same water bath to prevent the transmission of pathogens.
The best setup for home growers with a small collection of orchids is to soak individual orchids inside their own cache pot and ditch the water afterward.