If you have owned a Rubber Tree plant for more than a few months, hopefully, you’ve already witnessed a substantial amount of growth. These vigorous plants can put on several inches a season, but only if you ensure they have the nutrients they need to facilitate tissue production. Fertilizing provides the extra nutrition boost necessary to keep your plant thriving.
To ensure your Rubber Tree is healthy and flourishing, you should fertilize once a month during the growing season with a balanced fertilizer, diluted to half strength. Rubber Trees aren’t huge feeders, but providing additional nutrients will help them develop their long, glossy leaves and strong, tall branches.
Fertilizing typically isn’t on the top of everyone’s to-do list, mainly because it can quickly become confusing. My intent with this article is to explain why Rubber Trees need to be fertilized and then to dive into the details, like N-P-K ratios, liquid vs. granular, and organic vs. synthetic. Hopefully, by the end, you’ll have all the information you’ll need to feed your Rubber Tree and be rewarded with lots of healthy growth.
Why Rubber Trees Need Fertilizer
It’s no secret that Rubber Trees are great growers. It’s not uncommon for them to put on several inches of growth during one season, often requiring you to pot them into a larger container several times over the course of their lives.
So, what creates that growth? As long as Rubber Trees, and most other houseplants, for that matter, have access to sunlight, water, and carbon dioxide, they can create their own food through the process of photosynthesis. That food is what provides the energy for the plant to survive.
Aside from an energy source, however, a plant also needs nutrients and minerals that are essential in many internal structures and chemical reactions (some of which boost photosynthesis). Plants can draw these nutrients from the soil they are planted in, but because we confine our houseplants to pots, over time, the soil can get depleted as those resources run out. At that point, it is necessary to supplement with fertilizer.
Fertilizer is essentially just a combination of these natural minerals that aid in your plant’s ability to utilize the food they create and to grow. We often refer to fertilizer as “plant food,” but that is incorrect. Fertilizer is more like a multi-vitamin for your plant, providing essential building blocks for many important processes.
It’s pretty common to see store-bought potting soils already fortified with a slow-release fertilizer, so most plants you purchase or have just repotted typically have enough nutrients to last them for six to nine months.
However, as your Rubber Tree grows, those nutrients can quickly become depleted. Although Rubber Trees aren’t heavy feeders, they do need nutrients available to them at certain times to develop strong, tall branches that support their big, glossy leaves, so it’s always best to ensure the soil is sufficiently fertilized.
A Quick Note on Growing Seasons
When considering the health of your Rubber Tree and whether or not to fertilize, you should always consider what time of year it is.
This is because Rubber Trees, like many houseplants, have a distinct growing season. Typically, during a growing season, the plant is actively putting out growth and developing new branches, leaves, and perhaps flowers or fruit. When its growing season ends, the plant tends to go dormant.
The growing season for Rubber Tree plants is typically early spring through fall, when temperatures, sunlight availability, and other environmental factors are most ideal for facilitating growth. During the growing season, you’ll notice that your Rubber Tree requires more water and fertilizer.
At the end of the growing season, as winter approaches, growth above the soil slows down or stops completely while the plant focuses on root health and growth to prepare for the colder months ahead. During this time, the plant requires much less water, sunlight, and nutrients.
This is important to understand because fertilizing outside of your Rubber Tree’s growing season, at best, won’t make any difference in the plant’s growth, and at worst, will create a situation where the excess fertilizer built up in the soil can actually burn the plant’s root system, causing lasting damage.
If your Rubber Tree is not in its growing season, hold off on giving it any fertilizer until it comes out of dormancy in the spring.
What Fertilizer is Best for Rubber Trees?
Figuring out what fertilizer is best to use on any specific houseplant can be a bit overwhelming. There are many different options to choose from, in many different forms, so deciding on “the best” will depend on what you are hoping to achieve with a specific plant.
Understanding the NPK Ratio and the differences between organic or synthetic and granular or liquid are essential to picking out a fertilizer that will work for your plants. Let’s dive into each of these to get a better idea of what your Rubber Tree needs.
N, P, K Ratio
You may have noticed a series of three numbers on any bottle or bag of fertilizer you’ve ever picked up. These numbers indicate the amount of the three main macronutrients essential to your plant’s health; nitrogen, phosphorus, and potassium.
For example, a “well-rounded” fertilizer might have the numbers 10-10-10. In this case, 10% of the mixture is nitrogen, 10% is phosphorous, and 10% is potassium. We call it “well-rounded” or balanced because it has similar levels of each macronutrient mixed in.
Choosing the correct fertilizer will always depend on what type of plant you are trying to supplement. Each macronutrient is ideally suited for a different element of your plant’s growth, so knowing what your plant needs is essential to picking the right feed.
Nitrogen is essential for the process of photosynthesis in plants. It helps promote the leafy, green growth like leaves and stems. Phosphorus is more essential for root health and helps promote flowers and blooms. Potassium is great at aiding in growth, protein production, and disease resistance.
To put this another way, your lawn is essentially a big patch of new, green growth, so using a fertilizer high in nitrogen is going to provide the best nutrition. However, you grow tomatoes for the fruit, not the plant, so picking a fertilizer that has higher levels of phosphorus and potassium will help ensure blossom development and avoid common diseases like blossom-end rot.
Your Rubber Tree needs different macronutrients at different times. Younger plants benefit from a feed that is higher in phosphorus to help develop the root system, creating an established base for the plant to grow from. As it matures, though, something higher in nitrogen will help facilitate lots of stem and leaf growth for a fuller, taller, stronger plant.
Because of this, and the fact that Rubber Trees are relatively light feeders, I have always found it’s easier to utilize a “well-balanced” fertilizer so that plenty (but not too much) of all three macronutrients are available to the plant whenever it needs them. Something like a 10-10-10 would be perfect!
Organic vs. Synthetic Fertilizers
Deciding on the NPK balance in your fertilizer is the most important choice to make when picking out a feed for your Rubber Tree. After that, you can then explore the differences between organic and synthetic options.
Organic fertilizers are made up of ingredients that are natural sources of nitrogen, phosphorous, and potassium. Things like alfalfa meal, fish emulsion, bone meal, kelp, and manure are all ingredients that create the NPK ratio in an organic feed mix.
On the other hand, chemical fertilizers are typically made with natural or chemical components that are highly processed, so the resulting product is more concentrated and very precise in their NPK ratios.
While organic fertilizers have less of an environmental impact, they are typically more expensive. Because they are minimally processed, their nutrients aren’t immediately available to the plant. Often, these fertilizers break down in the soil, slowly releasing the macronutrients for the plant over more extended periods of time.
Alternatively, synthetic fertilizers come highly processed and, therefore, break down quickly, allowing your plant to utilize them much faster.
I, myself, am a big proponent of organic fertilizers and use them whenever I can. However, if I notice my houseplants are looking unhealthy and depleted, or their growth has slowed or stopped, I typically use a synthetic feed to give them a quick boost of nutrients to get them back on track.
Liquid vs. Granular Fertilizer
Another difference you’ll see in fertilizers is that they come as liquid (or water-soluble powder) or granules. I opt for liquid feeds most of the time because I feel like they are easier to use, and you can control the dosage better, but granular forms work well in certain applications, so I’ll explain both.
Granular fertilizers consist of small pellets that you spread over and then mix into the soil around the plant. The pellets break down over time, slowly releasing nutrients over a period of months. This is a good way to keep your potting soil charged with some nutrients for the plant to utilize at any time, but are harder to use if you find your plant suffering from a nutrient deficiency and need to take swifter action.
Liquid fertilizers are either a concentrated liquid or a powder that you dilute in water. Measuring amounts is usually very straightforward, and you can easily dilute the mixture with more water if necessary. Because the nutrients are already dissolved in water, they can be taken up by the plant’s roots quickly and efficiently.
My Fertilizer Recommendation for Your Rubber Tree
For most of my houseplants, especially my Rubber Trees, I always opt for the “well-balanced” formulas. I wrote above that I prefer using liquid, organic feeds whenever possible, so something like Espoma Organic 2-2-2 fertilizer is a great choice.
Because it’s organic, it has lower NPK numbers (typical due to the sources used), but I’ve found it does a great job with regular applications. Remember, Rubber Trees aren’t heavy feeders, so they are a good plant to use organic feeds on.
If you are looking for a great synthetic fertilizer, a blog favorite is Jacks All Purpose 20-20-20 Houseplant Fertilizer. It’s reasonably priced and comes as a powder that you dilute in water, so application is easy.
With Rubber Trees, I always recommend diluting your fertilizers to half strength to avoid burning your plant, but that standard rule commonly refers to 10-10-10 formulas. With Jacks, you can dilute it to a quarter strength for the same effect, so it lasts a long time.
The Dangers of Overfertilizing
Similar to seasoning your dinner, the same rule applies to fertilizing your plant. It’s easier to add more than to take the excess out. Always dilute your fertilizer!
Adding too much feed to your plant’s soil can burn the root system, making water and nutrient absorption difficult or impossible. Even if you follow the direction on the packaging, some feeds are just too strong for delicate houseplants, even if they are “formulated” for that specific application.
I always recommend diluting your fertilizer to at least half strength. I figure I can always add another round of diluted fertilizer if I don’t see the improvements I’m hoping for, which is a much better alternative to having to save a plant from nutrient burn.
You’ll typically see yellow or brown leaf tips as the first sign of nutrient burn. These are common signs of underwatering, so if you’ve recently applied a dose of fertilizer, it may have burned your plant’s roots and hindered water absorption.
You may also see scorching on leaf surfaces caused by too much fertilizer being absorbed at one time and being carried throughout the plant. Leaf tissue is delicate and can easily be burned by the excess chemicals and salts.
Another sign of over-fertilizing is the presence of a fertilizer crust on top of the soil. This is an accumulation of the excess feed and salts crystallizing at the surface.
Saving Your Plant from Fertilizer Burn
If you notice the signs of fertilizer burn early enough, you can try to mitigate the damage by flushing your soil as soon as possible.
Flushing the soil with water is the best way to remove the buildup of fertilizers and salts for the pot. Put your plant in the sink and turn the tap on low. Let water pour through the soil and out the drainage hole for about five minutes. This should remove whatever dissolved fertilizer is in the soil and prevent further damage to the plant.
However, there’s no fixing the damage already done. Any brown leaf tips or damaged roots probably won’t recover, and you’ll want to keep an eye out for any other damage developing after the flush out.
How Often to Fertilize Rubber Trees
As I’ve said, Rubber Trees aren’t big feeders in general, so fertilizing them is a fairly easy task. I recommend only fertilizing them with diluted liquid fertilizer (half strength or quarter strength, if using Jacks) once a month during their growing season.
If the plant is dormant during the winter, you can skip feedings all together until it begins to wake back up in early spring.
Now, because Rubber Trees are champion growers, this rule of thumb changes a bit if you’ve recently replanted them into a larger pot. Because most potting soil mixtures come pre-charged with a slow-release fertilizer, your Rubber Tree will be totally fine for the first 3-6 months after replanting.
Starting at three months after repotting, you can supplement what is already in the pot with diluted liquid feed on the monthly schedule, paying close attention that you aren’t burning your plant.
Because it is common to have to pot up Rubber Trees into bigger containers on an annual basis, you may only need to supplement fertilizer for a couple of months out of the year.
A Quick Note on Compost as Fertilizer
Many folks want to take their stewardship for the environment even further than using organic fertilizers and opt for using compost to provide nutrients to their plants.
This is perfectly acceptable as long as you have a good understanding of the compost you are using. Be sure that the compost you have has been fully decomposed and well-mixed. This helps avoid hot spots caused by microbes breaking down materials and highly concentrated pockets of nutrients that can burn your plants.
You should also be aware of the NPK ratio of the compost. Many people are often surprised at how low the macronutrient levels can be in seemingly healthy compost, so doing a soil test on it will help determine if there are sufficient amounts or too much of each macronutrient.
Lastly, be prepared to experiment a bit. Even knowing the nutrient levels in your compost, it is still less consistent than applying liquid fertilizer, so you may need to start small and check week after week to see if your plant needs additional nutrients.
Hopefully, you’ve learned a thing or two about all the different options you have when it comes to fertilizing your Rubber Tree and other houseplants. I prefer the ease and accuracy of store-bought, liquid fertilizers, but you have many other options to consider if you prefer to go a different route.
No matter what fertilizer you choose to use, remember that Rubber Trees only need small supplemental applications, only when they’re growing, so always dilute your feed. If you follow that rule, you’ll be setting your Rubber Tree plant up for tons of healthy, vibrant growth for seasons to come.