Most cactuses have spines, and their presence can also indicate how healthy your cacti are. If your cactus is losing its spikes or leaves, it will not look as decorative and might even die, depending on a cause. In this post, you will find reasons why your cactus is losing its spines (thorns) or leaves, what you can do to stop that, how to help your cactus grow new spines.
Few of the main reasons why a cactus might be losing its spines or leaves are pests (especially mealybug), lack of nutrients or fertilization. Less common reasons include overwatering, lack of sunlight and burns.
Reason #1: Pests
One of the main reasons why your cactus might be losing its spines is due to pest invasion. The most common cactus pest that causes loss of spines is mealybug.
Mealybugs are white in color, also resembling cottony substance. If your cactus is affected, you might notice mealybug on various parts of a cactus. But if there’s no white fluff anywhere on a stem, let your cactus dry out and take it out of the pot.
Then, examine its roots. If you see white residue on roots, it could be mealybug infestation. Mealybugs will suck out your cacti’s juices and lead to loss of spikes. If you leave it untreated, it will kill your cactus over time.
Nematode is another parasite that often hides in cacti roots, so most people find out too late about them. Because nematodes are too small to see, you will need to look for other symptoms. These symptoms include swollen roots, loss of cactus coloration and loss of spikes.
If you have previously had another type of a pest affecting your cactus, affected spots are likely to lose spikes. It can then heal, but not grow any new spikes if damage was too extensive.
You can read more about cactus pests and diseases in this post.
Reason #2: Lack of nutrients & fertilization
If your cactus is lacking nutrients or fertilization in the soil, it might start getting weak and losing its spikes or leaves. This can become an issue if for example, you haven’t repotted your cactus for more than 2-3 years, and have not fertilized it. The amount of nutrients in that soil would be low.
Lack of potassium, especially, can lead to loss of thorns on cacti. That’s why lower nitrogen and higher potash fertilizers are recommended for cacti.
Cactuses benefit from fertilization during the growth season. There are different types of fertilizers, like this one. Most are liquid ones that you need to dilute and use few times within the summer. Slow release fertilizers are also great for cacti, and feed plants for months.
Reason #3: Lack of sunlight
Lack of sunlight is another less common reason why your cactus might be losing its thorns. This is especially true if you have jungle/desert cacti and live in a colder climate.
Most cacti require bright sunlight, some requiring shading during hot summer afternoons and evenings. Even tropical cacti require bright but filtered light. If your cactus is not getting enough sunlight for an extended period of time, it will not grow and can start losing its spikes.
You can read about cacti light requirements in more depth here.
Reason #4: Overwatering or underwatering
Overwatering is a big issue with cactuses and can sometimes lead to loss of spines. If your cactus is in a sunny spot with warm temperatures, it will need more water. That’s especially true during growth season. Make sure that your cactus can dry before you water it again – always use containers with drainage holes only.
A common mistake that cactus owners living in places with cold winters make is not allowing their cacti go through dormancy period in winter.
If your temperatures in winter get low with not much sunlight, you need to take your cactus to a cool spot of around 55-59 (13-15 Celsius). Water your cactus lightly once in 4-6 weeks, but make sure to check soil is dry first.
Keeping your cactus indoors, especially by radiators plus stopping or reducing watering altogether will cause your cactus to start developing thin and elongated growth and loss of roots.
But even keeping your cactus indoors and watering often might easily cause overwatering, due to lack of sunlight. This in turn, might lead to loss of spines.
Underwatering can also be an issue with larger cacti that grow outdoors in hot climates. Shriveling of a cactus is a sign of underwatering. Plump leaves and stem is a sign of enough water stored in a cactus.
Reason #5: Turning your cactus too often
Cactuses don’t like being turned too often, especially when preparing to bloom. When you have cacti indoors and notice that your cactus is leaning, you need to turn your cactus so that its other side is facing the sun.
However, if your cactus is preparing to bloom, don’t turn it around. This will disturb its flowering process.
Reason #6: Rotting
If your plant is rotting, you might also see its spines falling off. Cactuses can suffer from dry or wet rot caused by bacteria and fungi.
In case of a dry rot, your cactus will become brown and start corking, often from bottom to top of the stem. If it’s a wet rot, the cactus will start appearing mushy and soft.
Try to squeeze your cactus a little – if there’s any resistance, that’s a good sign. Also, check the roots – do you notice anything unusual? If you do, replace the soil, disinfect scissors/shears and cut off any affected roots or parts of the cactus. Allow a week before watering and putting it out in the sun.
Reason #7: Physical damage
Another common reason why your cactus might be losing spines is due to physical damage to your cactus. Do you have any pets at home that could come in contact with your cactus?
Or maybe if your cactus is placed outdoors, could any small animals touch/push it? Spines on cacti can get easily detached with physical contact, especially when in contact with fur.
This can also happen if you knock it down, causing spines to break. Some cacti have glochids (furry spines), which can easily come off. Cacti in genus of Eriocacti (previously in genus Pariodia), are especially prone to losing their thorns easily.
What is more, there are many cacti with fake flowers for sale. Retailers attach fake flowers using hot glue most of the time, but sometimes pins as well. Hot glue damages the stem in the flower spot.
The best thing is to try to remove the flower, or let is come off over time. The damaged spot won’t regrow spines, but should heal over time. You can read more about fake cacti flowers and removing them in this post.
Thank you for reading this post on why cacti might be losing spines. If you would like to learn more about cacti care, see this resource page.