A bit like human nutrition, fertiliser for plants falls roughly into four levels. This free guide helps you decide which level you want to give your plants, and which level they need (which might not be the same thing!). You decide…
Caveat: This guide applies to the more common and huge rage of liquid fertilisers, since slow-release pellet or powder fertilisers can be hit or miss with indoor plants.
LEVEL 1: JUNK FOOD
To start with you have junk food. This level does provide nutrients. Not everything a plant needs, sure, but it some of the basics plant’s need. Typically at the very least, the ‘big 3’. That’s nitrogen, phosphorus and potassium, listed as NPK on the label.
But often not much else. Better than nothing! Still beneficial of course, but not really the ideal choice longer-term, especially for houseplants.
Usually cheap to buy too, but when you work out the cost per litre once diluted with water, you might get a shock as they are often already very diluted in the bottle to get the shelf price down, so you may find you use it up quickly and need to use a fair bit.
Why are indoor plants any different from outdoor plants when it comes to fertiliser?
An important side note here, as this is a common misconception about houseplants that can make indoor plant care more of a struggle than it needs to be. Understanding this bit also helps make sense of the different types of fertiliser.
Don’t treat indoor plants the same as outdoor plants when it comes to fertiliser.
Outdoors, the soil is typically finer as it’s designed to hold more water (since drying out is more common concern vs over-watering for us houseplant hobbyists).
It’s also typically much higher in organic content, and most importantly, it’s ALIVE.
The top layer of healthy outdoor soil can contain an estimated 100 million to 1 billion living microorganisms.
They get busy eating and breaking down organic material, turning it into those essential nutrients plants need.
It’s absolutely packed full of good guys, like beneficial bugs. Not just ones you can see like worms and springtails, but the majority are things you can’t see, like helpful bacteria, good fungi, protozoa and more.
Indoors? Not so much.
Some experts go as far as saying our indoor plants are in DEAD soil, or grow in sterile soil, but it’s not quite that dramatic.
There ARE some good guys in there, unless you’re growing in a fully sterile substrate of course (new leca and pon are two examples), or regularly treat with something like hydrogen peroxide.
In general though, there’s WAY less going on in the pot versus what their outdoor buddies benefit from.
And that lack of good guys means indoor plants lack the same ability to break down ORGANIC sources of nutrients.
One reason it matters more for indoor plants that their fertiliser not only makes up for what their soil can’t provide, so offers more than level 1 fertilisers do. but also provides nutrients in a bioavailable source, that do NOT need to be broken down first.
That’s why specialist indoor plant fertilisers typically include a LONG list of synthetic nutrients on the guaranteed analysis on the label. And provide more than just organic nutrient sources like seaweed.
Some fertiliser brands take it next level and really hold our houseplants hands, such as avoiding urea - the most common nitrogen source used in fertilisers - or chelating the metal minerals, which can otherwise get ‘locked’ in the soil, unable to be absorbed by the roots.
Urea needs an extra couple of steps for plants to break it down into the essential nitrogen they need, and nitrogen is the big one houseplants generally need the most of.
Some plants struggle or can’t do that urea step at all. One reason orchids get their own urea-free fertiliser options, but that’s right up at level four.
Okay, back to the four levels. Here’s level two…
LEVEL 2: Happy Medium
Next up is complete but ‘middle-of-the-road’ or 'medium' fertilisers. A bit like a healthy home-cooked meal with a little of everything on the plate, or like a multi-vitamin supplement.
(for the purists, fertiliser is not literally food of course, just painting the picture)
This level offers plants a lot more than just NPK, sometimes all 12 essential nutrients, sometimes some extra beneficial ones added into the mix also.
A big step up from level 1 for your plants, but more convenient for YOU than level 3 or 4.
Having one fertiliser for all your plants means they get all the essentials they need in general (hopefully, check the label!); without having the hassle for you of using different fertilisers to match their current needs better (that’s level 3), or for their unique genetic requirements or adaptations for their natural habitat (that's level 4).
Some level 2 fertilisers also offer a mix of synthetic and organic sources of nutrients, some may be fully synthetic, but you’re less likely find purely organic fertilisers at this level.
One clue is the guaranteed analysis on the label.
The 12 essential nutrients:
Look for at least the following if you’re wanting all the essential minerals for your houseplants:
Nitrogen (N)
Phosphorus (P)
Potassium (K)
Calcium (Ca) > Note this one might be missing, even at this level
Magnesium (Mg)
Sulfur (S)
Iron (Fe)
Manganese (Mn)
Zinc (Zn)
Copper (Cu)
Boron (B)
Molybdenum (Mo)
One example up at this level is GT Complete Focus (I added the links below to the best picks for each level).
GT Complete Focus has all the 12 essential nutrients above, all tested and listed on the label. No urea either. All in the final, synthetic form too, so they are immediately available for indoor plants.
The beneficial nutrients:
Some fertilisers add extra nutrients, like Superthrive does, which in their case includes chlorine, cobalt and sodium.
Not essential, and some would argue not needed or even possibly harmful for indoor plants (depending on the level of course - remember ‘the dose makes the poison’ as the saying goes)
But keep in mind some brands which are marketed to indoor plants, are also used for outdoors plants or edible crops, that might need those extras.
LEVEL 2: Best match fertilisers
A couple of top picks for ‘happy medium’ options for your plants at this level:
LEVEL 3: LIFE-STAGE FERTILISERS
The next level up is where you match your fertiliser to your plant’s life-stage.
A bit like a home-cooked meal with increased levels of protein if you were lifting weights at the gym; or adding a folic acid and iodine supplement to an already healthy diet if you’re pregnant.
Those broad life-stages are:
Vegetative maturity (foliage)
Your plant’s focus at this stage is more on foliage and its support systems. The plant is busy growing strong stems, leaves and a bigger root system, ready to support flowering.
Flowering (buds and blooms)
This is the process from peduncles and buds through to when flowering finishes, ready to reproduce.
Pollination, fertilisation, fruit / seed formation and seed dispersal
Combining multiple stages in one here - but skipping these steps for the purpose of this guide - since our houseplants don’t typically go through these stages.
Propagation
Not officially a separate life-stage by itself, but I added it in here because we definitely pay a LOT of attention to this stage in the houseplant hobby.
There are lots of specialist nutrients available for the propagation stage too, like GT Clonex, GT CCS and NurtureSystem No.3 RapidRecovery (links for those below too).
Foliage or Flowers?
This is the big one. As so many houseplants are grown for their foliage, level 3 foliage fertilisers is where you’ll find the biggest selection of indoor plant fertiliser options.
Nitrogen fuels foliage growth over flowers, so higher nitrogen levels on the label are a giveaway (if the name doesn’t make it obvious), like GT Foliage Focus or Superthrive Foliage-Pro.
Other best sellers like Plant Runner’s Indoor Plant Food and trending NurtureSystem PowerGrow don’t say it in the name, but the nitrogen levels and other nutrient ratios tell you they are formulated for foliage first.
The other half of level 3 fertilisers is flower or bloom fertilisers.
They will normally be lower in nitrogen and higher or have changes to phosphorus, potassium and calcium levels, plus other changes in nutrients further down the list.
If you’re doing everything right and still not getting flowers, your fertiliser may be to blame.
(but do check light and other conditions first, as fertiliser is further down the list of importance than fertiliser companies might have you believe)
Higher nitrogen levels send plants a message to make the most of it while it's available, and focus it’s efforts on foliage, as leaves are like a plant’s solar panels - sometimes even to the point it slows down, stops or prevents flowering!
For indoor plants like hoyas, peace lilies, African violets, flowering anthurium and more, you can switch from a foliage to a flower fertiliser. Like GT Flower Focus or Superthrive Bloom (links for both coming up).
Some hobbyists just stay on a flower fertiliser all year-round, treating it more like a level 2 fertiliser.
If your plants could talk, they'd prefer being switched from a flower food back to a foliage fertiliser after flowering has finished. That shifts their focus back on roots, stems and leaves, helping them recharge and get ready to fuel next season’s blooms.
Look out for calcium (in a good way)
A good flower or bloom fertiliser should list calcium on the label too, usually up high around the 4th position in the guaranteed analysis, but do check the label as not all fertilisers include calcium!
A calcium deficiency can cause bud blast (where buds form but fail to bloom), shorten flowering time, and increase premature browning of new flowers (and new growth in general, one reason calcium is a popular inclusion for variegated foliage plants too).
LEVEL 3: Best match fertilisers
A few top foliage options:
Plant Runner Indoor Plant Food >
NurtureSystem No.1 PowerGrow >
And a couple of flowering options too:
Not forgetting some top propagation picks:
GT Clonex > Dip fresh cuttings in this protective rooting gel
GT CCS > Specialist root growth fertiliser for propagating
NurtureSystem No.3 RapidRecovery > Supports root growth during propagation and for root rehab
LEVEL 4: ADAPTATION FERTILISERS
Fancy name, but up at this level the options get really specialised. Best analogy that comes to mind using human nutrition as an example, would be along the lines of a celiac diet.
Up here is where you’ll find specialist fertilisers with adjusted formulas made for a plant’s unique genetic traits, often evolutionary adaptations developed in response to their natural habitats.
Orchids are a perfect example of a level 4 plant. You’ll also find specialist formulas for succulents, African violets and more up at this level.
That does not mean that list of 12 essential nutrients changes in these level 4 fertilisers, but how MUCH of each nutrient, and even the SOURCE of those nutrients, will usually have been adjusted.
(I say usually, as I’m well aware some brands just change the name and market it differently on the outside without changing the formula on the inside, but I’m giving them the benefit of the doubt for the sake of this guide)
Using orchids as our example, they get their own fertiliser for a few reasons. One is how they grow. In nature, they often hang off the side of trees, absorbing nutrients from rainwater, animal waste and debris as it washes by, gets stuck in the bark or in their often sprawling, cage-like roots. No soil to help break things down or protect them either.
That makes orchids more sensitive than most, with typical fertilisers at risk of scorching or killing their roots, or nutrients reaching toxic levels fast.
Also a reason your typical urea-based fertilisers are also a no-go in general for orchids. Urea needs those soil microbes to break it down into nitrogen. Level 4 fertilisers like GT Orchid Focus Grow and Bloom are guaranteed urea-free.
LEVEL 4: Best match fertilisers
GT Chilli Focus > (this one’s not in NZ yet as I write this but it’s due late 2026 so should be here by the time you read this)
Which fertiliser is best for your indoor plants?
Personally, I think you're best to pick the fertiliser level from this list that works for you AND your plants.
What's the point going all in at level 3 or 4 if you're not going to bother switching fertilisers for each plant? It has to work for you too, or your plants still miss out.
Yes, level 2 is better than level 1, and level 3 is better than level 2, but the fertiliser you give them is better than the fertiliser that just stays unopened on the shelf.
Plus, if you prefer to make one big batch up of nutrient solution in advance for everyone, absolutely go for level 2.
Now you know the levels, why they exist and how to pick between them, the rest is up to you - but all means ask me if you're still feeling stuck,
I'm pretty much brand agnostic, although I have my favourites of course based on my own experience, and I'm always happy to help a fellow houseplant hobbyist.
ABOUT THE AUTHOR: Anna is the owner of plant store Love That Leaf which specialises in products and advice for indoor plants. She is also the resident indoor plants writer for NZ Gardener magazine. Her houseplant care articles appear in print in magazines in-stores NZ-wide, and online on Stuff, The Post, NineHoney and more.