What month should I stop fertilizing houseplants?

There is no month that works for every reader. The daylight half of our test is failed from about October to February in London, New York and Stockholm, from November in Los Angeles, in the middle of the year in Sydney, and never in Manila. That is astronomy rather than opinion, and it is why we test rather than pick a month.

When should I start fertilizing houseplants again in spring?

The same two tests, read in the other direction. The northern lines on the chart above clear the 11-hour daylight bar from about March, Sydney clears it from September, and Manila never drops below it. One thing we do not model: the common advice to skip a plant you bought or repotted in the last few months. Our growth check does not know about that, so that call stays yours.

When do houseplants go dormant?

We do not hold a dormancy date, we run a test that can flip on any day. A plant is treated as resting when the room is below the minimum for its type, or when neither the day length nor the reading at its spot clears the light bar. Two plants a couple of metres apart in one room can be on opposite sides of it in December.

Can I keep feeding through winter under a grow light?

Yes, and the bar is lower than a grow light. Any spot reading above 1,200 lux passes the light half of the test on its own, which an ordinary bright windowsill clears. Warmth still has to pass separately.

Why does GrowSpot treat my plant as resting when the room is warm?

Because warmth alone is not enough. The plant needs both a warm enough room and light, from long days or from the spot itself. In a dim corner in December neither route is open, so it is treated as resting even in a warm flat.

Does feeding pause during a heatwave?

Yes. An active heat or cold alert outranks both other tests and suppresses feeding while it runs, on the reasoning that a plant under stress cannot use it. The repot hint stands down on the same signal.

What happens if I have never taken a light reading?

The plant is treated as resting rather than growing. The app will not assume the bar has been cleared for a spot it has never seen, which is the same reason it says it cannot assess a spot rather than guessing at one.

When to Stop Fertilizing Houseplants

Stop in October, start again in March. That is the answer at the top of the results, and it is repeated by nurseries, forums and the summary above them all. It is good advice in the place it was written for.

GrowSpot cannot use it, because it has readers in both hemispheres and at every latitude, so the feeding decision had to be made out of things that can be measured anywhere. It ended up as two tests, and the plant has to pass both.

Worked example: Ocean Spider Plant two metres in from a north window, air 21 °C and 45% humidity, light airflow. Your spot will score differently. Run it for your own spot →

The month is really a latitude

The first test is light, and the calendar-free version of it is day length: above eleven hours of daylight, the season is treated as one a plant can grow in. Day length is astronomy, so it can be worked out for anywhere from a date and a latitude, with no weather involved:

The amber line is the 11-hour bar the growth check uses. Each point is the middle of that month. Day length is pure astronomy (latitude and the date, no weather and no forecast), so this chart is the same every year. Manila never drops below the bar, Sydney crosses it in the middle of the year rather than at the end, and only the northern lines behave the way "stop feeding in October" assumes. London and Los Angeles sit between the two northern lines, clearing the bar from March to September and March to October.

Read the Manila line against the advice we started with. Near the equator the daylight test is never failed, so "stop feeding in October" is not a mild simplification there, it is the wrong answer for every month of the year. Sydney fails it in the middle of the year rather than at the end, and the two northern lines are the only ones behaving the way the advice assumes.

Indoors, the same room has two answers

Day length is not the only way to pass the light test. A reading above 1,200 lux at the spot itself passes it too, which is how a plant under a grow light stays in growth through the winter. It is also how an ordinary bright windowsill does, because that bar is lower than people expect. Hold the window and move only the distance:

The amber line is the 1,200 lux bar the growth check uses. Estimates for an indoor position on a clear day, from the same model the spot checker uses. The line crosses the growth bar between 2.5 and 3 metres in. On one December day that puts a plant on the sill on the growing side of the test and one at the back wall on the resting side. A south window is a different room for this purpose: it starts at 13,000 lux and is still above the bar at the back wall, so the same question has a different answer on the other side of the flat.

The bar falls between two and a half and three metres in from a north window. That is the useful sentence on this page: on the same December day, in the same room, a plant on the sill is still growing by this test and the one by the back wall is not, and no calendar can tell them apart. Our page on how far from a window plants can live works that fall-off through in detail.

The whole test, including the part that outranks it

The second test is warmth: the average temperature has to sit above the minimum for that type of plant. And an active heat or cold alert overrides both, pausing feeding whatever the season and the sill say:

The room, and the plant in it	What GrowSpot calls the plant	Which test decided it
Warm room, long summer days	Growing, so feeding makes sense	Warm enough, and light enough
Warm room, short winter days, plant in a dim corner	Resting, so feeding is suppressed	Neither the day length nor the spot clears the bar
Warm room, short winter days, plant on a bright sill	Growing, so feeding makes sense	Warm enough, and light enough
Cold room, long summer days	Resting, so feeding is suppressed	Below the minimum for its plant type
Warm room, short winter days, no reading taken	Resting, so feeding is suppressed	Neither the day length nor the spot clears the bar
Any of the above, with a heat or cold alert running	Paused, so feeding is suppressed	Weather alert outranks both other tests

Run through the growth check itself. Rows two and three are the same room on the same December day, and the only difference is where the plant is standing: a reading above 1,200 lux at the spot satisfies the light half on its own. That is a low bar, an ordinary bright windowsill clears it, and it is the reason the calendar answer breaks down indoors.

The row worth pausing on is the fifth. With no light reading taken, the plant is treated as resting rather than growing, because the app will not assume a bar has been cleared on your behalf. That is the same reasoning behind the honest verdicts elsewhere on this site: an unread spot is unknown, not fine.

What to do with your own plants

Stop feeding when the plant stops growing, which is what every source says, and take the two measurable halves seriously: is it warm enough, and is there enough light where the plant stands. If you have a bright sill and a heated room, some of your plants may not need a winter break at all, and the ones two metres behind them will.

Take a reading at the spot before you decide, with the free spot checker if you would rather not install anything. If the plant is already unhappy, feeding is rarely the fix and four things change at once in winter. If you were also planning to move it into a bigger pot, that has a season and three other conditions of its own.

The thresholds here are read out of the growth check itself, and the light figures are estimates for an indoor position on a clear day, not meter readings from a real room. The minimum temperature is held per plant type, and we do not publish those figures, because they are working defaults rather than calibrated ones. Day length is exact and identical every year.

Plant photo credits

When to Stop Fertilizing Houseplants

The month is really a latitude

Indoors, the same room has two answers

The whole test, including the part that outranks it

What to do with your own plants

Questions, answered honestly

Find the right spot.