This Houseplant Mistake Could Kill Off Your Collection in September – Plant Pros Explain How to Avoid It
It's time to put the fertilizer away until spring
With summer coming to an end, it's time to turn our attention to fall houseplant care. Shorter days and cooler room temperatures call for reduced watering, relocating plants, and – crucially – no more fertilizing.
Arguably, it's the biggest September houseplant mistake you can make. Feeding plants when they're slowing down and entering a period of dormancy will only cause more harm. Chemical fertilizers in particular can burn roots, leading to foliage damage and the overall decline of your plant. Ultimately, fertilizing houseplants now can weaken and kill them off.
Having said that, it's important to note that every houseplant has its own set of needs and in some cases you can give houseplants one final feed in September before fall. Here, houseplant pros explain everything you need to know.
Why You Should Stop Fertilizing in September
Even though fertilizer is a key element of your houseplant care kit, it should only be used when houseplants are actively growing. This is because fertilizer (like this indoor plant feed from Walmart) contains essential plant nutrients that support plant growth. When a plant isn't actively growing, this can overload plant roots and damage the plant.
'When a plant’s growth slows, it cannot use nutrients as quickly. Continuing to fertilize at the same frequency can cause excess salts to build up in the soil. Over time, this may damage the roots and lead to brown leaf tips, yellowing leaves, or a white crust on the surface of the soil,' explains houseplant expert Rosalin Ortega.
As part of fall houseplant care, it's also important to help your houseplants adjust to the changing conditions. Many houseplants struggle with sudden changes in light and temperature, which can cause drooping, leaf drop, and the general decline in health. Fertilizer on top of this can cause shock, resulting in damage like discoloring foliage.
'Too much fertilizer can also encourage weak growth when the plant does not have enough natural light to support it. More fertilizer will not make up for a lack of light. It may actually place more stress on the plant,' Rosalin explains.
For this reason, it's best not to fertilize houseplants come September – though there are a few exceptions.
Rosalin Ortega is the founder of All About Planties, an online houseplant shop helping beginners choose plants they can actually keep alive. She shares practical, real-world guidance on indoor plant care
The One Exception
With different indoor plants having different needs and behaviours, there are occasions where you can do one last feed in September.
'I recommend watching the plant rather than relying only on the calendar. If it has stopped producing new leaves, the soil is drying much more slowly, or its overall growth has noticeably slowed, it is probably time to pause fertilizing until spring,' says Rosalin.
'Some tropical indoor plants, including pothos, philodendrons, monsteras, and spider plants, may continue producing new growth through fall if they are kept in a warm room with plenty of light. These plants may still benefit from occasional feeding, but I would reduce the frequency and use a balanced fertilizer at half strength,' she continues.
'Other plants are more likely to slow down significantly as the days get shorter. Alocasias and caladiums may begin entering dormancy, while naturally slow growers such as ZZ plants and snake plants will usually need little or no fertilizer once their growth pauses,' Rosalin adds.
The best thing to do is research your specific plant's growing needs, and observe for new growth. But, if you are unsure, the safest option is to put the fertilizer away until spring.
'The conditions inside the home still matter. Plants growing under a full spectrum LED light (like this grow light from Amazon) may remain active longer than plants relying only on limited fall and winter sunlight,' Rosalin adds.
When to Start Fertilizing Again
To know when to start fertilizing your houseplants again, look for signs of new growth in early spring.
'Regular fertilization is necessary during the period of active growth: spring and summer. You’ll need to gradually increase feeding throughout this period, starting with small doses to help your plant awaken and adjust to new conditions,' advises Plantum plant expert Marina Prokaten.
If you have particularly fast-growing, low-maintenance houseplants (like monsteras, palms, and pothos), you might want to opt for a slow-release, granular fertilizer over a concentrated liquid feed. This slow-release houseplant feed from Amazon, for example, can be applied in early spring, providing a consistent supply of nutrients over multiple weeks.
Marina Prokaten is a resident plant expert for the Plantum app, which helps users identify plant species, diagnose their conditions, and get specific care advice. She has three years of experience consulting on botany-related topics for Plantum.
What to Shop
Don't be fooled. Despite the garden settling down for fall, there's much to do in our indoor gardens. In particular, there are a few indoor plant jobs many people forget to do. This includes checking on the underside of leaves for common indoor plant pests and getting rid of them quickly to stop infestations taking over your entire houseplant collection.
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