Despite what fertiliser companies would have us houseplant hobbyists believe, it's not as simple as 'Never stop feeding your plants, even in winter'...
PRO TIP > Here's what's REALLY going on and how to know if YOUR plants in YOUR conditions need to be fertilised over winter > Should you feed your indoor plants in winter?
...if you decided what was best for your plants was NO fertiliser over winter, when should you start feeding again?
A common problem in spring, when it should all about lots of lovely new growth, is the complete opposite. Yellowing, browning, dying leaves and leaf drop. It's not just natural aging. And it IS normally preventable.
It's what you did (or didn't do), in winter that could be to blame
The number one cause when it happens in spring is NOT what everyone blames it on. It's not over-watering. Or under-watering. Or pests.
The main cause is not feeding in winter - or if you skipped the fertiliser in winter for good reason - it's leaving it too late to start feeding again when spring rolls around.
That's because the number one cause of leaf yellowing and death in spring is actually a simple-to-fix nitrogen deficiency.
I say simple because it's the first ingredient in fertiliser (the 'N' in 'NPK), and if you pick the right fertiliser, it can be a fast fix too.
The bad news is you can't reverse or heal the damage done. Plants don't work like us in that way. They just grow new leaves.
The good news is getting your timing right for when you start feeding again for growing season CAN prevent it happening in the first place.
Plus in most indoor plant foliage fertilisers - like best-sellers GT Foliage Focus, Plant Runner's Indoor Plant Food, NurtureSystem's No.1 PowerGrow and Superthrive Foliage-Pro - the one ingredient they all have the most of is nitrogen, for good reason.
The new growth myth
You might have heard yellowing in new growth means a nutrient deficiency. But that's NOT true for all nutrients.
For some nutrients, like the all-important calcium (that not all fertilisers include by the way), a deficiency DOES show up in new growth.
But that's NOT true for nitrogen. That's because nitrogen is a mobile nutrient (and calcium is not).
If you don't give your plants enough nitrogen over winter, or don't start feeding soon enough before spring, and you see quite even yellowing happening across most of the leaf at the same time and on older leaves, you've probably found the culprit.
But if you've seeing mottled yellowing, yellow halos around spots, yellowing only on leaf tips or edges, or yellowing only between the veins, look up the cause here instead > Why leaves turn yellow and how to fix it
Without enough nitrogen available for the roots to send to fuel new spring growth, plants steal what they need for new leaves by sacrificing old leaves, 'sucking' out the nitrogen and sending it elsewhere.
That's also why you should never cut off yellowing leaves. They can be a sign your plant is on life support right now. Here's what to do instead >
When to start feeding plants to avoid spring death
When it comes to the #1 essential nutrient nitrogen, a plant will uptake nitrogen quite quickly, within 24 to 48 hours, depending on the form it's in.
BUT it can take from 3 days to 4 weeks to make a visible difference in our plants and get to where it needs to be.
As a general rule to follow when it comes to nitrogen (without knowing your fertiliser of choice), that means you ideally want to start feeding again 4 weeks before spring to be on the safe side. But there is a shortcut.
It helps to know what form the nitrogen is in. You'll see some fertiliser brands advertising that they are urea free. Urea's the most common form of nitrogen used in most fertilisers.
The problem when it's needed fast however, is that plants can't use urea directly. Extra steps are required for the urea to be broken down so plants can actually get the nitrogen they need.
For indoor plants in ideal conditions, it tends to take 1 to 4 weeks for microbes and enzymes in the soil to convert urea into nitrogen.
But some plants lack the required soil microbes and enzymes that break down the urea, so they miss out entirely. Especially plants grown in sterile substrates like leca and pon, or soil-free substrates like bark.
That's a big reason why knowing the form nitrogen is in matters more for our houseplants often grown in soil-free potting mix versus outdoor plants grown in soil.
If you rely on an organic fertiliser that can also slow down how long it takes before the plant can actually access vital nitrogen. As fast as 3 to 4 weeks in ideal conditions depending on the form it's in, or as long as 2 to 12 months!
The spring shortcut (or when it's too late)
If spring is closer than 4 weeks away - or you're already seeing yellowing and suspect a nitrogen deficiency - consider a urea-free, synthetic, water-soluble fertiliser like GT Foliage Focus or Superthrive Foliage-Pro, for faster uptake of nitrogen (and all the other essential nutrients), to fix any nutrient deficiencies faster to get back to happier, healthier plants much sooner.
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.