Search this and you get lists, and they are not the same list. Four university extension services name between two causes and thirteen for the same symptom: impoverished soil, the wrong pH, root-bound pots, transplant shock, the wrong season, too much water, too little, pests. Every list is accurate. None tells you which line is yours.
Here are the four, with what each of them names. The counts spread across that whole range. One cause appears on every list, and it is the one this page is about.
| Published by | How many causes it names | The one all four name |
|---|---|---|
| yardandgarden.extension.iastate.edu | 2 | “The typical cause of spindly growth is low light levels.” |
| ipm.ucanr.edu | 5 | “Decline in houseplant health is most commonly associated with improper watering (too much or too little water provided), improper fertilization amounts, root diseases, poor sanitation, and adverse environmental conditions, such as low light intensity or low relative humidity.” |
| extension.sdstate.edu | 5 | Under insufficient light: “Slow or no new growth.” and “Leggy appearance.” |
| extension.illinois.edu | 13 | “Leggy, or stretching plants occur when they are reaching for more light.” |
Most of them are also answering about a garden. The threads on the first page are about vegetable beds and crops that have not gained four inches in two months, and Google splits out an indoor version of the question as a search of its own. Indoors the list is shorter, and one item on it can be settled with a number rather than a guess.
Great fit
This plant should be happy in this spot.
Just the right amount of light
Comfortable temperature
Humidity suits it
Airflow isn't quite ideal
Most of the time the room is not the reason
Here is an ordinary indoor spot, three metres into a room with a south window, with seven different plants standing in it one at a time. Nothing about the room changes down the table.
| The plant standing there | What the light is doing | Verdict |
|---|---|---|
| Monstera | Just the right amount of light | Great fit, 93/100 |
| Golden pothos | Just the right amount of light | Great fit, 94/100 |
| Snake plant | Just the right amount of light | Great fit, 94/100 |
| ZZ plant | Just the right amount of light | Great fit, 94/100 |
| Peace lily | Just the right amount of light | Great fit, 94/100 |
| Fiddle leaf fig | A little dim, but workable | Worth a try, 65/100 |
| Jade plant | Too dim here | Not the best fit right now, 40/100 |
Five of the seven are fine there. The fiddle leaf fig is not, and the jade is not remotely. So the honest answer to “is my spot the problem” depends entirely on what is standing in it, which is the one thing a list of ten causes cannot tell you and a score can. If your plant is one of the five, you have crossed off the one item on those lists that answers to a number, which is worth more than it sounds when checking the rest means disturbing the plant. If it is growing but stretching rather than filling out, that is a different symptom with a much narrower list.
The figures are estimates rather than meter readings. We build them from the window direction, the distance and a clear day, on the same curated care data the app scores with; your own spot will read differently, which is what the free checker is for.
Both ends of the room are flagged, and the reflex goes the wrong way
The instinct, when something is not growing, is to move it nearer the window. Here is what that walk actually costs, with the same plant and the same room:
| How far into the room it is | Estimated light | What the light is doing | Verdict |
|---|---|---|---|
| 0.3 m, against the glass | 13,000 lux | A bit bright, but workable | Worth a try, 65/100 |
| 1 m back | 10,000 lux | Just the right amount of light | Great fit, 92/100 |
| 2 m back | 6,300 lux | Just the right amount of light | Great fit, 93/100 |
| 3 m back | 3,969 lux | Just the right amount of light | Great fit, 93/100 |
| 4 m back | 2,500 lux | Just the right amount of light | Great fit, 92/100 |
| 5 m back | 1,575 lux | A little dim, but workable | Worth a try, 64/100 |
Read the ends. Against the glass it is flagged at 65, five metres back it is flagged at 64, and everywhere between one and four metres it holds 92 or 93. The room has a wide comfortable middle and two bad edges, and the reflex move, from the middle towards the window, is a move from 93 to 65. A little dim and a bit bright are both flags; only one of them looks like a problem from across the room.
That matters because relocation is itself on every one of those cause lists. Move a stalled plant on a hunch and you can end up holding two problems: the original one, undiagnosed, and a fresh one you introduced. Reading the spot first is the cheap half of this.
When the light checks out, the flag can be somewhere else you can measure
Crossing light off is not the same as crossing the spot off. Take a prayer plant one metre from an east window, in light it is entirely happy with, and change nothing but the air in the room.
The light reads the same the whole way. The verdict does not: the plant sits at worth a try from 20% right through 40% humidity, and only becomes a great fit once the air comes up to 50%. A spot can pass on light and still be the reason nothing is happening, and dry air is the version of that people are least likely to suspect in a room that feels comfortable to them.
What this cannot tell you
It cannot see the pot, so a root-bound plant reads the same as a comfortable one. It cannot see the soil, so nutrients and pH sit outside it entirely. It cannot see pests. And it does not know what month your plant thinks it is: one that stops in November and starts again in March is doing the correct thing. The seasonal version is a separate page, because the fix is different. If the spot scores well and nothing has moved in three months, that is real information: stop rearranging the room and look at the roots.
Published August 19, 2026 · Last updated August 30, 2026
