Under the right conditions, a Dieffenbachia can grow into a glorious houseplant with a wealth of exquisite foliage. To help yours fulfill that potential, you’ll need to give it a healthy amount of fertilizer. Striking the right balance is essential, though, because adding too much fertilizer can harm your plant. Our detailed guide will help you supplement your Dumb Cane’s diet safely and effectively.
Fertilize your Dieffenbachia only when it’s actively growing; outside of tropical climates, that will typically be in the spring and summer. We recommend using a synthetic liquid fertilizer so that you can easily control the dosage. Start at ½ or ¼ of the recommended strength and step it up gradually until you find the level at which your Dumb Cane thrives.
You can also get good results with slow-release fertilizers, including organic ones or natural soil amendments like compost. However, they’re less useful for correcting urgent deficiencies in your Dieffenbachia’s nutrition. And remember, no matter what kind of fertilizer you use, proper soil composition and watering technique are important if you want to avoid over-feeding your plant.
Your Dieffenbachia’s Nutritional Needs
The energy that powers a plant’s vital functions comes from the sunlight it absorbs through its leaves. But in the same way that a healthy diet for humans involves more than just calories, healthy plant growth requires more than just photosynthesis. Your Dieffenbachia also needs to take up some nutrients from the soil in order to survive and grow.
Nitrogen, phosphorus, and potassium are at the top of the list, but smaller amounts of minerals like magnesium and calcium are also essential. In the wild, these elements make their way into the soil from all kinds of sources – rainwater, decaying organic matter, windblown dust, and so on. But an indoor Dieffenbachia relies on you to replenish the nutrients in its pot.
Commercial potting mixes almost always contain some fertilizer, so if you planted your Dumb Cane in store-bought soil, it may still have some nutrient reserves. But if you don’t replace those nutrients as your plant uses them up, it will stop growing and eventually waste away to nothing.
Choosing a Fertilizer for Your Dumb Cane
Picking out the right fertilizer for your plant can feel a little bit like trying to order at a restaurant with a 10-page menu. There are so many options on the market that it’s easy to be overwhelmed. Fortunately, you can tune out a lot of the hype and focus on a few key considerations.
The labels of commercial fertilizers often sport a sequence of three numbers, often marked “NPK”, “N-P-K”, or “N:P:K”. These numbers represent the three main macronutrients that plants get from their soil: nitrogen, phosphorus, and potassium. They’re shown as percentages; a 20:20:20 fertilizer is 20% nitrogen, 20% phosphorus, and 20% potassium by weight.
You’ll encounter lots of claims that this or that ratio is great for root growth or flower production. This is mostly nonsense. Pretty much all plants use these three elements in the same ratio – 3:1:2.
That means that, for example, giving a plant a whole bunch of high-phosphorus “bloom booster” fertilizer won’t make it flower more than normal. At best, it can make up for a phosphorus shortage, but so will an ordinary “balanced” fertilizer. Your plant will use exactly as much of each nutrient as it needs, and any extra amount will simply sit in the soil – potentially harming the roots if enough of it builds up.
If you like the idea of giving your Dieffenbachia the exact right balance of nutrients, use a formula with a 3:1:2 NPK breakdown or an equivalent ratio like 6:2:4 or 9:3:6. You can also simply choose a balanced blend like a 10:10:10. As long as the soil has good drainage and you occasionally flush the pot (more on that later), the slight departure from the perfect ratio shouldn’t hurt your Dumb Cane.
Liquid, Granule, or Slow-Release Fertilizers
Fertilizer comes in different forms. Some kinds are sold as a liquid or powder that you mix into your Dieffenbachia’s water. Others come as granulated dust you can sprinkle onto the soil. Then there are the slow-release fertilizers – resin-coated beads or spikes that dissolve little by little as you water your plant.
Slow-release fertilizers are probably the easiest to use because all you need to do is add a spike or a pinch of pellets to the soil every 3-6 months, then water your Dumb Cane as normal. Because they break down so slowly, there’s little risk of damaging the roots with an overdose of fertilizer. And even if you’re very forgetful, it will take a long time for your Dieffenbachia to run out of nutrients.
Liquid fertilizers are at the opposite end of the spectrum. They require more care to use, but they offer more precision when it comes to dosage. And your Dieffenbachia can absorb and consume them as soon as they hit the soil. That comes in handy if your plant is suffering from a nutrient deficiency and you want to fix it right away.
Granular fertilizers fall somewhere in the middle, acting faster than slow-release formulas but offering less control than liquid ones. In general, they’re more useful in an outdoor garden than a houseplant’s pot.
Organic or Synthetic Fertilizers
You’ll also need to choose whether to use a fertilizer manufactured from processed chemicals or one that’s derived from natural ingredients like seaweed or bone meal.
Synthetic fertilizers offer more precision when it comes to nutrient levels, and they’re ready for your Dieffenbachia to gobble up right out of the package.
Organic fertilizers are more like the slow-release variety we described above. They’re made by breaking down more complex ingredients, and that process is usually not 100% complete by the time you apply them to the soil. Their nutrients won’t be available to your Dumb Cane until helpful microbes have digested them further.
On the plus side, many organic fertilizers have additional benefits for your Dieffenbachia, such as enriching the soil structure and adding the aforementioned plant-friendly bacteria. And there are solid environmental reasons to use organic fertilizer. For one thing, they require much less energy to produce.
Compost deserves special mention here as a particular type of organic “fertilizer” with its own unique strengths and drawbacks. The environmental appeal of turning kitchen scraps into plant vitamins is obvious, and compost can also help aerate the soil and nurture beneficial microorganisms.
However, you should keep in mind that compost tends to contain less nutrition by volume than commercial fertilizers, even organic ones. And if it’s not fully decomposed, it could burn your Dumb Cane with the heat it releases as it continues to break down. If you’re making your own compost, it’s important to let it sit for a while to “cure” even after it appears to be finished.
Our Fertilizer Recommendations for Dieffenbachia
We usually recommend using a liquid fertilizer with your Dumb Cane so that you can easily calibrate the level of nutrition you’re providing. Aquatic Arts Ficus Plant Food is a good choice. It’s made with all-natural ingredients, and although it’s marketed for Fiddle-Leaf Figs, its 3:1:2 NPK ratio works just as well for Dieffenbachias.
If you prefer a fast-acting synthetic formula – useful if your Dieffenbachia is dealing with a severe nutrient shortage – try Dyna-Gro Foliage Pro or Jack’s Classic All Purpose Fertilizer. The latter has a hefty 20:20:20 NPK ratio, so it will require more dilution before you apply it to your plant, However, that also means it gives you a lot of nutrition for your dollar!
When and How to Fertilize Your Dumb Cane
There’s one crucial point to remember when it comes to your plant’s diet: adding fertilizer only helps your Dieffenbachia grow if it has everything else it needs. You should only worry about nutrition when your plant has enough sunlight, water, humidity, and space to produce new stems and leaves. If even one of those ingredients is lacking, adding fertilizer will hurt rather than help.
In temperate climates, you can generally stick to fertilizing during the spring and summer, since these tropical beauties typically slow down or stop growing as the days get shorter.
If you’re using a slow-release pellet fertilizer, simply mix the appropriate dose into the soil at the beginning of spring and forget about it. Compost works best when you mix it right into the soil during repotting. Roughly 10% of the total soil volume is usually a healthy amount.
Liquid fertilizers require a more frequent application – typically once every 2-4 weeks. When it comes time to fertilize, mix up the appropriate amount of powder and water in a bottle, bucket, or watering can, stirring or shaking until it’s fully dissolved. Then use it to water your Dieffenbachia as you normally would, saturating the soil until you see water draining out of the pot.
Your fertilizer’s packaging will have dosage instructions, but we recommend diluting it to a weaker concentration at first – ½-strength if you’re fertilizing once a month or ¼-strength if it’s every 2 weeks. You can always increase the dose later, but accidentally fertilizing too much can seriously harm your plant.
On a similar note, it’s often a good idea to start with a weaker dose at the beginning of the growing season, gradually increase it to the full amount, then taper it back down as you head into autumn. Over time, you’ll get a feel for how much fertilizer your Dieffenbachia needs to thrive, but it’s best to be cautious when you’re just starting out.
The Risks of Using Too Much Fertilizer
Why is it so dangerous to overfertilize your Dumb Cane? The problem is that any nutrients your plant can’t use will remain in the soil, typically in the form of mineral salts. When these chemicals accumulate to a high enough concentration, they stop your Dieffenbachia’s roots from taking in water.
The result is predictable: dehydration. Your plant’s foliage will start wilting, withering, and turning crispy. The leaves usually dry up at the tips first, since those are the parts furthest from the moisture reserves in the base of the pot.
You may see the same symptoms if you’re giving your Dieffenbachia too much or too little water, or if its air is too dry. But if you’re using synthetic fertilizer and you’ve ruled out watering and humidity issues, there’s a good chance that you’re dealing with fertilizer burn.
Treating Fertilizer Burn in Dieffenbachias
An excess of fertilizer salts can pose a serious problem for your Dumb Cane’s health. Fortunately, you should be able to wash the surplus minerals out of the potting mix with a quick soil flush.
Place the pot in the sink and give it a thorough soak with distilled or filtered water. You’ll need a decent amount; the general rule is to use 3 or 4 times the total volume of the container. Pour it in slowly, letting it permeate the potting mix and flow out through the bottom of the pot.
This should rinse out most of the built-up salt compounds, but it won’t undo the damage that the roots and foliage have already suffered. If any of the leaves have died completely, snip them off. This will free up energy that the plant can use to send out new growth. You can also trim away crispy leaf tips and edges to clean up your Dieffenbachia’s appearance, but leave any healthy tissue in place.
Make sure that you disinfect your pruning scissors before each cut, or you could give your Dumb Cane an infection. Wipe the blades down with a cloth dipped in rubbing alcohol or a 10% dilution of bleach. Always wear gloves when cutting a Dieffenbachia – the juice of this plant can irritate the skin.
Preventing Fertilizer Burn
We’ve already mentioned that you should fertilize only during the growing season and start with weaker doses. But there are a few other ways you can lower your risk of overfertilizing your plant.
First of all, a soil flush like the one described above can be a helpful preventative measure even when your Dumb Cane isn’t showing signs of fertilizer burn. We recommend performing one every 1-2 months when you’re actively fertilizing your Dieffenbachia.
Proper watering habits make a difference too. Some houseplant owners like to hydrate their plants in small “sips”, adding a little bit of water each day. This is actually counterproductive. It’s better to water thoroughly, wetting the potting mix all the way through so that water drains out the bottom. This kind of watering serves as a mild soil flush in its own right, helping to wash salts out of the pot.
For the same reason, the danger of fertilizer burn is lower if your soil blend has good drainage. For Dieffenbachias, we recommend an equal mix of coarse perlite, coconut coir, orchid bark, and African Violet potting mix. Read more about the best types of soil for Dieffenbachias in this article.
Signs That Your Dieffenbachia Needs Fertilizer
It’s not always easy to recognize a nutrient-deprived plant. Your Dieffenbachia can hang on for quite a while in the absence of fertilizer before it starts to show obvious signs of distress.
The first indicator is usually that your plant simply isn’t growing. In optimal conditions, a Dumb Cane can put on two feet of growth or more within a single year. If yours is receiving lots of bright, indirect light but still isn’t getting any taller, it might need a dietary boost. Undersized, pale, yellowing, or misshapen leaves can also indicate a lack of nutrition.
Remember that these symptoms can also result from overwatering, underwatering, or a lack of adequate lighting. Don’t start increasing the fertilizer dose unless you’re sure that one of those other issues isn’t responsible.
Do Dieffenbachias Like Coffee Grounds?
You may have heard that some indoor gardeners like to feed leftover coffee or coffee grounds to their houseplants as a form of natural fertilizer. This isn’t a totally crazy idea – coffee is an organic substance that contains a bit of nitrogen and a few other nutrients. But can it work for your Dumb Cane?
The answer is yes – in moderation. Coffee helps to acidify the soil slightly, which Dieffenbachias appreciate, and it will add a little nutrition to the soil as it decays. It won’t act as a replacement for a full-spectrum fertilizer, though, and you don’t want to add so much that the caffeine poisons the roots.
Limit yourself to occasionally dumping the dregs of your coffee pot into your Dieffenbachia’s pot. Always wait until it’s cooled off completely, and don’t include any cream or sugar, as these may attract pests.
Don’t empty out your coffee machine’s filter into your Dumb Cane’s soil, though. Large quantities of coffee grounds are usually too dense for the confined space of a houseplant’s pot. They can cause drainage issues and increase the risk of root rot. You’re better off tossing your grounds onto the compost pile and letting them decay into humus.
Healthy nutrition is key to unlocking the exuberant foliage that makes a Dieffenbachia such a fantastic houseplant. Start small, slowly increasing your plant’s fertilizer diet until you have a solid feel for its needs. With enough care and patience on your part, your Dumb Cane will grow big, bold, and beautiful.