It’s a common misconception that because cacti are desert plants and have adapted to survive in some of the harshest conditions, they don’t need to be fertilized.
However, when growing cactus plants at home, in a more controlled environment, it’s highly recommended that you give your plants some fertilizer to encourage them to grow and even flower.
You must remember though, that cacti require a different type of fertilizer in a more diluted form than other common houseplants. The fertilizer you choose should have slightly more phosphorus than nitrogen and it should also contain beneficial soil microbes such as probiotics and mycorrhizae as well as humic acids.
To understand this better, we need to look at the natural environment where cacti grow. Desert regions have dry soil that is occasionally improved with a small amount of decaying plant matter or humus. This soil mostly consists of mineral compounds.
In addition, it rains infrequently but when it does, it pours. This short burst of heavy rain is the only time that cacti can take up nutrients from the soil along with as much moisture as they can hold.
This would indicate that cacti have adapted to absorbing occasional nutrients in the form of simple compounds but only at certain times when it actually rains.
Therefore, their nutritional requirements are quite distinct when compared to other types of plants. For this reason, we need to evaluate the most important elements that a cactus fertilizer must contain to grow happy and healthy plants.
Choosing The Correct NPK Balance
NPK is the formula by which all commercial fertilizers are made. It’s a combination of three main elements:
- Nitrogen for strong plant growth
- Phosphorus for excellent root production and healthy plant cells to ward off diseases
- Potassium for promoting flowering and fruiting
When selecting the correct fertilizer for cactus plants, the NPK should be relatively well balanced with slightly more phosphorus (P) than nitrogen (N). The entire concentration of NPK should also be relatively low as too high a concentration will burn your plants.
It’s also important to try and select an organic fertilizer as this is usually milder than one that is made from chemical compounds.
Why Are Humic Acid And Soil Microbes Important?
Cactus plants require simple organic compounds to aid their growth and keep them healthy. That’s why humic acid can be important because it helps to break down the minerals in the soil into these simple compounds.
Humic acid contains natural macromolecular compounds that normally exist in any soil as well as in plants and animals. This material is sourced from sedimentation layers that have developed primarily from peat bogs before the material has become hardened enough to form coal.
In essence, humic acid contains a mixture of carbon, oxygen, nitrogen, phosphorus, and hydrogen. Its primary purpose is to unlock nutrients in the soil in order to make these nutrients readily available to plants.
On the other hand, soil microbes such as Mycorrhizae and probiotics keep the soil alive and improve the nutrient content.
When looking at fertilizers for your cactus plants, never consider fertilizers that are designed for lawns. Although these fertilizers do contain many of the required nutrients, they are often high in nitrogen which is not what you want for your cactus plants.
What Type Of Fertilizers Work Best For Cacti?
We’ve discussed how cacti in their natural habitat can only absorb nutrients when it rains. Therefore, we can assume that liquid fertilizers are the best solution for feeding our cactus plants.
Let’s look at some liquid fertilizers that would work best.
Commercially Available Cactus Fertilizer
If you’re fairly new to cactus growing, it would be advisable to purchase a specific liquid cactus fertilizer that you can buy from your local garden center or even online. These commercially available fertilizers will contain all the nutrients that your cacti need.
Plus, they usually come with comprehensive instructions on when and how much fertilizer to apply to your plants.
Liquid Seaweed Fertilizer
Liquid seaweed is another type of fertilizer that can be used on cactus plants. It has a lower concentration of NPK but does contain plenty of microbes, minerals, and humic acid.
When using this type of fertilizer, just make sure that you dilute it adequately. In general, you should dilute to half the strength that is recommended for regular houseplants.
If you make your own compost and have one of those compost tumblers, it most likely has a plug in the bottom that you can undo to release the liquid. This liquid is high in nutrients and minerals and can be used as cactus food.
But, make sure that you dilute it with water before using it on your plants. You might have to do a little experimenting to get the formula just right but start with a higher dilution, to begin with, and see how your plants respond.
If you have a worm farm, you can also use worm tea on your cactus plants. Wom tea comes from worm castings and contains a multitude of nutrients such as calcium, magnesium, carbon, and nitrogen. This type of fertilizer also helps to balance the pH in the soil mix which means that nutrients are much more readily available to your plants.
Once again, you want to dilute your worm tea to at least quarter to half strength before giving this solution to your cactus plants.
Slow-Release Fertilizer Pellets
As an alternative to using liquid fertilizers, you could also consider using slow-release fertilizer pellets but you must select a brand that is designed for cacti in order to get the right mix of nutrients.
These pellets only need to be applied once a year and will release their nutrients when you water your plant. This makes the nutrients available to your cacti when they need them the most and can uptake them with the moisture in the soil.
Using Coffee Grounds
Believe it or not, coffee grounds are actually great as a fertilizer for cactus plants. The grounds contain higher levels of phosphorus and potassium and lower levels of nitrogen. This is an ideal cactus food for cacti.
One thing to watch out for though is that coffee grounds can be quite acidic. This is perfect if your soil has a high pH but not so good if the soil is acidic. In general, cacti prefer a fairly neutral pH level of around 6 to 7. So, if you’re going to be using coffee grounds on your cacti, keep an eye on the pH level of the mix that they’re growing in.
Coffee grounds are particularly useful for Christmas cactus as they help to promote flowering and will give your plants a much-needed boost.
Here’s how to prepare your coffee grounds to use them as a fertilizer:
- Spread the grounds out on a large tray or plate and allow them to dry. You don’t want them to stay moist for long because mold will start to grow quite quickly.
- Store the dried grounds in an open container so that no moisture collects.
- To use the coffee grounds, you can either stir them into the water that you use on your cacti or just scatter them over the soil mix and rake them in a little.
Eggshells contain the mineral calcium carbonate which is ideal for cactus plants. This particular mineral will strengthen the plant’s cells which, in turn, promotes strong growth. Calcium is also important for strong root growth.
The best way to fertilize your cacti with eggshells is to make eggshell tea. Here’s what to do:
- Wash the eggs shells thoroughly making sure that no egg yolk or egg white remains on the shells.
- Place the dry shells into a glass jar and cover with boiling water. A mild ratio is around 10 eggshells to 1 gallon of water.
- Leave the shells in the water overnight.
- The next day, strain the eggshells and any other particles from the water.
- You can now use this water to feed your cacti.
Alternatively, you can make eggshell powder to use as a fertilizer. Here’s what to do:
- Wash the eggshells like before.
- Leave the shells to dry out completely. You can also place them in the oven on low heat for around 20 minutes to fully dry them out.
- Grind the shells into a powder using a coffee grinder or similar.
- Sprinkle the powder over the soil mix and lightly rake in.
Bear in mind that eggshells alone will not give your cacti all the nutrients that they need, so you will still need to use another fertilizer to add all the essential nutrients to your plants.
When Should You Apply Fertilizer To Your Cactus Plants?
Fertilizer should only be applied to your cacti during their active growing period which is mainly spring and summer. Depending on the type of cactus that you’re growing, you should only need to apply fertilizer once a month during late spring and summer.
In winter, your cactus plants will be dormant and should not be fertilized at all. This goes hand in hand with the reduced watering schedule at this time.
How To Recognize Nutrient Deficiency In Your Cactus Plants
You’ll find that cactus plants won’t show too many signs of nutrient deficiency early on. This is because they’re not heavy feeders but tend to take up nutrients slowly whenever they get watered.
Look out for color lightening especially at the base of the plant as a sign of potassium or nitrogen deficiency. You see this mostly at the base because the plant will direct any available nutrients to the growing parts first.
If there is any deficiency present, there will also be a slow down in growth overall.
On the other hand, if your cactus is suffering from a phosphorus deficiency, you’ll notice this in a lack of flowers and subsequent fruits.
If you’re growing Christmas cacti, a lack of potassium will cause the leaves to turn yellow and they may even die and fall off the plant. Add a dose of coffee grounds to the soil mix as this will quickly fix the problem.
Even though cactus plants are not heavy feeders, they still need to be fertilized during their growing season. When growing in their natural habitat, they obtain nutrients from the soil whenever it rains. Even desert soils have nutrients and minerals in them that are replenished by decaying plant matter.
However, when we grow cacti indoors in containers, after some time the available nutrients in the soil mix will have depleted and there will be none left for the plant to absorb through the roots.
Therefore, it’s important to apply a dose of fertilizer with the right ingredients to your cactus plants at least once a month during late spring and summer. However, because the plants are dormant during winter, there’s no need to fertilize them until they’re actively growing again.
See more: How to care for cactus indoors