Watering your cacti is a difficult task. It’s not always easy to tell if they’re getting enough or too much water, which can sometimes lead you to make poor decisions on how often and when. That’s why I did a month-long experiment. Ready for the results!
Cacti cannot live with too much water. A one-month-long watering experiment on cacti clearly showed that just after seven days of overwatering, some cacti might show some distress signs and might die just after 25 days. Overwatering signs include the following:
- Plumped stems,
- Mushy Stems,
- Sunken Brown Spots,
- Ruptured Stem, and
- Rotten Smell.
Are you in doubt if you’re providing your cactus too little or too much water? Worry no more, as I have provided below a guide on how much and how often you should water your cactus.
Four cacti from two different species are gathered and set up inside my greenhouse.
One cactus of each species will be overwatered (test cacti) while the other (reference cacti) will not. Reference and test cacti are as close as possible at the start of the experiment.
The sample species are established and well-rooted on the same gritty potting medium to make the comparison sensible.
The cacti specimen collected are:
- Two potted Gymnocalycium Mihanovichii ‘Moon Cactus’ (Red and Orange) – the scion of this specimen is sensible to overwatering
- Two potted Gymnocalycium Damsii ‘Chin Cactus’ – prefers regular watering.
Each pair of specimens has one test sample and one reference/control sample for comparison.
The specimens are placed inside the greenhouse side-by-side, where they can get the same sunlight every day. The reference specimens were watered regularly (once every week), while the test specimens were drenched twice a week (more often than usual) for one month. The experiment setup remained on the same spot for a month.
The specimens were monitored regularly to detect any emerging signs of overwatering. I snap photos of each sample every week or when I spot a noticeable change.
After seven days of excess watering (twice a week), the test sample shows off its chunky muscled ribs (see black circle). On the 14th day of the experiment, both the reference and test samples grow flower buds (zoomed photo in white circles). The flower bud of the test sample develops faster compared with the control sample’s bud.
Above, you can see the result comparison between the test and reference samples at the end of the experiment. The first and apparent change from the overwatered Gymnocalycium damsii was it gets plumped up in just seven days. Due to too much water, its natural reaction is to absorb as much water as its roots can take.
The overwatering on Gymnocalycium damsii took effect after seven days as it gets plumped up. However, the case of Gymnocalycium mihanovichii ‘moon cactus’ is different.
Overwatered moon cactus gradually loses its original color after around 20 days. Its orange color gets paler with a little yellowish on the base of the scion. Meanwhile, the rootstock Hylocereus species has no evident signs of overwatering.
On the 25th day, I noticed an unsightly change from the moon cactus test sample (see photo above). The scion turns paler, mushy to touch, and has a hollow part on the side. The cactus also emits a disgusting rotten smell. These are the dangerous signs of overwatering.
I leave the cactus for another three days to see if further signs will unfold. After 28 days, the cactus became worse, almost brown and drooping on one side (see photo below). Throughout the experiment, the rootstock remains unchanged, with no evident signs of overwatering.
This evidence reveals that the moon cactus scion (the top) is sensitive and intolerant to too much water than the Hylocereus rootstock. The scion has no chlorophyll, so it does not perform photosynthesis. The rootstock supplies more and more moisture on the scion with continuous watering until all the storage space runs out.
As a result, the scion turns soft, probably burst out from too much liquid, and eventually rot and die.
The roots being the first-hand receiver of water, must probably be reacting with excessive moisture. Let’s check how it was underneath the overwatered cacti.
At the end of the analysis, all samples specimens were removed from their pots for root check-up. After root examination, I discovered that moon cactus roots were almost dead and rotten. It is soft, readily falls apart, without new growth.
While the overwatered moon cactus roots are disintegrating, the G. Damsii roots are reacting in another way. The root system seems to grow happily with continuous watering. The test sample has more roots compared with the reference cactus. It shows that G. Damsii can tolerate steady watering for a month because it developed lush roots that absorb excess water.
Generally, having too much water is the easiest way to kill a cactus. While most cacti are sensitive to too much water, some species can tolerate excess water in a short while.
Cacti can survive a long drought period, but sitting on an oversaturated soil is detrimental to them. Overhydration can kill a cactus if not save on time. The effect of overwatering happens rapidly on rot-prone cacti, and it can be fatal in most cases. It is crucial to pay close attention to your cacti and determine their water requirements.
One can detect dangerous signs of overwatering a few weeks after the plant is saturated. At first, the plant looks like it is growing healthy and happy, but underneath, the roots are suffering. The last thing you know, the signs are widespread, and there’s little you can do to save it.
Here are the signs of overwatering:
Puffed-up stems are an early sign that the cactus is getting more water than usual.
The rib muscles are becoming prominent, and their skins are shiny.
The plant’s roots absorbed lots of water and stored them on their spongy stems, making them chunky and plumpy. It may be a good sign, but watch out, as this initial indication will lead to more serious trouble. At this point, you need to cut back from watering and save your cactus from root rot.
Overwatered cactus will gradually change from its vibrant color to a duller or paler hue.
Cactus sitting on a wet medium for an extended period will suffer from root rot. Damaged roots are incapable of transporting nutrients to the whole plant leading, as the first sign, to color loss or Chlorosis. As observed from the experiment, the moon cactus color is fading due to overwatering and root rot.
When you notice a color change, take an instant action to inspect the roots and save your plant from dying.
Excess water inside the cactus stem saturates the plant tissues, disrupting the cell structure. From there, the stem tissues become soft and watery to touch.
When a cactus absorbs too much water, chances are, cell storage packets will run out of space and burst from the inside. Because of that, cactus stems become mushy and yellowish/ brownish. There is a chance of survival with mushy cactus, but it depends on the degree of damage.
Severely hydrated cactus will develop sunken brown spots over time. It is because the cactus becomes soft, and some parts of the stem sink in.
Mushy cactus stem sinks because its tissues are so soft. The stem structure is no longer compact, and it cannot hold all the tissues together. In this case, the chances of survival are close to none.
As the cactus takes up more moisture, its stem expands to make more room for the extra water. Too much expansion leads to rupture of the stem.
If the medium stays wet for too long, the cactus will keep absorbing water until it becomes oversaturated. The root’s ability to efficiently absorb water makes the cactus expand to the extent that causes the stem to split open. Splitting will not kill your plant because it will just callus eventually. Just hold back from watering until the cut is healed.
The mushy stem eventually rots due to the formation of pathogens. The rotten portion gives off a foul odor.
As the root rots, some portion of the plant rots as well, releasing an unpleasant odor.
Even if the cactus has evident signs of having too much water, they are savable, but it depends on the condition of the plant.
Overwatering is more severe than underwatering because the effect of too much water is irreversible. The impact of overwatering can spread rapidly within the plant, and if not rescued sooner, the cactus will succumb to death.
When your cactus is at the initial level of overhydration, please take action to save the plant as soon as possible before it reaches the point where the root rots. Cut back from watering and inspect the plant for other possible signs. In extensive damage, like portions of the roots and stems are rotten, save the healthy part or propagate the offsets.
The frequency and amount of water a cactus needs depends on 1) potting medium, 2) size of the pot, 3) season/ climate, 4) type of planter used, 5) cactus variety, and 6) size of the plant.
Watering is the most challenging part when growing a cactus. Most often, beginners find it hard to get right on watering, and it is the usual reason they kill their plants. There is no specific quantity and frequency when watering a cactus. However, a general rule of the thumb is to allow the potting medium to dry up between watering.
Here are the factors I considered when giving my cactus water:
Ensure that the potting mix is fast draining for success when growing a cactus. It is always recommended for cactus to have a gritty, well-draining medium to avoid waterlogging.
A well-draining potting mix allows the excess water to drip off the pot and allows the mixture to dry out quickly. Ideally, most cactus with well-draining soil require once a week watering. Always let the potting medium dry out before watering again. Any commercial potting mixture containing worm castings, coco coir, and pumice like the one below from Amazon will do.
The water takes longer to dry out and evaporate for medium in large pots, while the water evaporates quickly in small containers. Also, shallow pots allow the water to dry up faster than deeper pots, reducing the risk of waterlogging.
The majority of cacti do well in smaller containers, as they hate sitting in a pool of water for too long. Cacti planted on oversized pots are more prone to root rot. It is crucial to use pots with adequate drainage holes.
In general, during winter, most cacti are dormant. Also, the temperature is cold, so water does not evaporate quickly. It means they need less water or once every month.
However, in spring and summer, where the temperature is high, and most cacti are actively growing, the need for moisture is high. During this time, once a week or more, frequent watering is required. The water needs of your cactus depend on the season and temperature of your area.
The planter used has a role in the watering schedule. A terracotta pot and unglazed ceramic pot help absorb excess moisture and promote aeration on the roots, reducing the risk of overwatering. Plastic and fiberglass pots do not drain effectively, so watering must be monitored.
Likewise, metal pots have poor drainage and heat up under high temperatures. It will affect the root system of the cactus.
This terracotta planter below is best for medium-sized cactus.
Every cacti species has its water requirements. Some cacti would love a bit of moisture, others hate high humidity, and a few prefer the damp environment.
The majority of cacti species do not like sitting on saturated, compact soil. Frequent watering will cause their roots to rot, and the next thing you know, they are on the brink of death. It is essential to understand the water needs of your cacti so you will know when to rehydrate them properly.
Essentially, cacti with lots of thick spines might need more but infrequent watering than thinned spines species. Spines help the cactus conserve water by blocking the surface’s airflow and creating an insulating layer that lessens evaporation and transpiration.
Furthermore, cacti with sturdy stems do well in storing significant amounts of water. If you have a columnar or globular cactus, you can water them deeply but sporadically. Due to their low surface area to volume ratio, they can store water efficiently. Most of these cacti can survive with a bit of moisture retained on their medium.
In contrast, smaller cacti with fewer spines and potted on a small container require frequent watering and closer attention. They tend to lose water quickly, and small containers dry up easily.
Cacti with soft stems tend to get mushy easily when overwatered. Moreover, species with thin root systems are more prone to root rot due to waterlogging. Variegated cactus with fewer to no chlorophyll content are more prone to rot with excess moisture. If you have these types of cactus, you need to pay attention to their water needs. Water them when their potting medium is dehydrated.
While others need more water sporadically, and some are sensitive to constant watering, few species thrive in humid surroundings. They are the unique epiphytic cactus that love to stay moist but not wet. Rainforest epiphytes like to stay moist so they can hold on to trees for long periods.
Most cacti that do not like too much water are slow growers, have fewer or zero chlorophyll, and are soft-stemmed. They are some of the species that cannot tolerate overwatering.
For instance, Rebutias, Astrophytums, and Mammillarias prefer infrequent watering due to soft stems and slow growth.
I have a slow-growing cacti species such as Lophophora cactus, and I found out that it needs low water. Due to its slow growth, the plant utilizes lesser water from its stem. It does not like overwatering and will rot easily when the medium gets oversaturated. I water my Lophophora once every two weeks, and it’s doing good.
Variegated or mutated cacti such as moon cactus do not like overhydration because their scion is chlorophyll-less. Cacti without chlorophyll do not perform photosynthesis, so water consumption is low. My moon cacti receive water once every 7 -10 days.
Another example of cacti that do not like overwatering is the mammillaria species. Mammillaria typically has soft succulent stems. Their stems can barely hold enough water and tend to get mushy with too much water absorption.
Cacti that need more water are those that have large compact stems and are spherical or columnar. They can withstand over-watering for a short period.
Gymnocalycium Damsii, like the one from the experiment, have a spherical shape and compact stem. It survived a month-long frequent watering without developing dangerous signs of rot. In addition to Gymnocalycium are Echinopsis and Parodia, they can tolerate excess water for a short while.
Gymnocalyciums, Echinopsis, and Parodia species love more water because of their compact stems that store enough water. Furthermore, the Epiphytic cactus loves damp environments.
You may think that the bigger a cactus, the more often it has to be watered. This is not entirely true.
Larger cacti must be watered deeply but infrequently. The larger the cactus, the smaller the surface area, the bigger the volume. Therefore, large cacti have a lesser chance of water loss due to evaporation.
Larger cactus can tolerate a short period of persistent watering because it has a bigger volume to store the excess water. On the other hand, smaller, younger cacti such as seedlings have a higher growth rate and need more moisture to replenish the water loss during growth. Small cacti planted on small planters need frequent watering.
On top of it all, the most effective way to avoid overwatering is by using the soak-and-dry method or bottom watering. When watering, drench the whole pot until the water runs up to the top portion of the potting medium. Remove the pot from the water and let it drip.
Wait until the potting medium dries out completely before watering again. This method also reduces the salt build-up on the potting mix because deep watering will wash off the accumulated salt.
- Generally, cacti cannot survive too much water. This will cause root rot. Waterlogging is the common cause of cactus death.
- An overwatered cactus will appear plumped, discolored, soft to touch develops sunken brown spots. Excess water can cause the cactus to expand and eventually crack. Due to rotten roots, some parts rot as well and emit a foul odor.
- Factors such as the potting medium and the cactus variety must be considered when watering the cactus.
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