Houseplant Statistics: The Published Numbers, With Their Sources

Every figure below comes from a government agency, a cooperative extension service, or a peer-reviewed report, and links to the page it was taken from. Nothing here is a survey run by this site, because this site does not run surveys.

Market-size figures are deliberately absent. Most "houseplant statistics" pages are built from industry reports that sit behind a paywall, cannot be checked by a reader, and say nothing about whether a plant will live in your apartment. The numbers collected here are the ones that change what you do.

Light, in foot-candles

Illinois Extension publishes a four-band scale, and the whole of this site is calibrated against it.

Band	Illinois figure
Low	Low Light (75 foot candles)
Medium	Medium (average) Light (150 foot candles)
High or bright	High or Bright Light (300 foot candles)
Direct	Direct (1500 foot candles)

Twenty times as much light between the bottom band and the top one, and both of them exist inside an ordinary room.

For the upper end measured at the glass rather than in a room, UGA Extension reports that at east-facing windows, Footcandle readings at these windows can reach 5,000-8,000.

Those two sources are not in conflict. Illinois is describing what a position provides across a day; UGA is describing the direct beam while the sun is on that side of the building. A single number attached to a window is always a summary of something that moves. Worked through in east vs west facing windows and estimated for your own room by the window light estimator.

Daylight across the year

At 40 degrees north, roughly the latitude of Philadelphia, Denver and Columbus, day length runs from 15 hours 1 minute at the June solstice to 9 hours 20 minutes at the December solstice. That is 5 hours 41 minutes gone.

These figures are transcribed from the US Naval Observatory sun tables rather than quoted, because that page is a query form rather than an article. They are reproducible: enter a date and a latitude and the table returns them.

The rate is what matters, and it is not steady. In the week around the September equinox the day shortens by about 19 minutes. In the week before the December solstice it shortens by about 1. The loss arrives while nobody is watching and stops once everyone has noticed. Charted in houseplant winter care.

Humidity

Two published ranges, measuring different things, and both are true at once.

Figure	Source	What it describes
Many houseplants prefer a relative humidity of 40 to 50 percent	Iowa State	What foliage plants prefer
The American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) recommends that indoor relative humidity (RH) be maintained between 30% and 60%	ASHRAE, via Penn State	What a building is run at

A home held at 35 percent sits inside the ASHRAE range and below what Iowa State says most houseplants want. Nothing is wrong with either number: they were written for different subjects. See how to increase humidity for houseplants.

At the other end, humidity has a ceiling that is a disease risk rather than a comfort question. NC State puts gray mold's preferred conditions at temperatures from 60-70 °F coupled with high relative humidity (>85%), which is a fair description of a planted glass cabinet in a heated room.

Temperature

Maryland Extension gives the target: foliage indoor plants grow best between 70° and 80°F during the day and from 60° to 68°F at night.

The figure worth knowing is the one below that range, because it contradicts what people assume about cold. Clemson states that Chilling injury can occur to many tropical plants although temperatures do not drop below 32 °F.

Freezing is not the threshold. A windowsill in the low fifties on a winter night is enough, and the damage from the colder end of that range can be invisible. See houseplant cold damage.

Plant exposures reported to poison centers

This is the section that changed what this site says about its own subject.

America's Poison Centers publishes the National Poison Data System annual report each December, free, as a PDF. The figures below are from the 2024 report, available from the annual reports index.

Plants as a share of all reported exposures, from Tables 17A, 17C and 17D, which rank substance categories by frequency for different groups:

Group	Plant exposures	Share of that group's exposures
All human exposures (Table 17A)	54,556	2.14%
Children five and under (Table 17C)	30,044	3.53%
Adults twenty and over (Table 17D)	15,601	1.23%

Set the first two rows against each other and something falls out that no houseplant page seems to mention: more than half of all reported plant exposures are children under five. That is arithmetic on two published figures rather than a figure the report states, so treat it as such. Plants also make up nearly three times as large a share of exposures among the under-fives as among adults.

Common houseplants inside the top 25 plant exposures, from Table 20:

Plant	Reported exposures
Elephant's ear	1,098
Epipremnum aureum (pothos)	837
Monstera deliciosa	499
Zamioculcas zamiifolia (ZZ plant)	479
Spathiphyllum (peace lily)	477

Rank positions are not given here. The rank column did not survive text extraction from the PDF cleanly, while the counts did, so the counts are reported and the placings are not.

Every one of those five is a calcium-oxalate plant, which is the group houseplants toxic to cats and dogs sorts them into. The oxalate group is the painful-rather-than-dangerous one, and the report's own category name for all five is "Plants: oxalates."

What this reframes. That article is written for pet owners, which is how almost every page on this subject is written. The data says the exposures being reported are overwhelmingly small children. A shelf that is out of reach of a cat and a shelf that is out of reach of a toddler are different shelves.

If a child or a pet has eaten part of a plant, call Poison Control or a veterinarian rather than reading a page about it. Poison Control is 1-800-222-1222 and ASPCA Animal Poison Control is (888) 426-4435.

What is not on this page, and why

No market-size or industry-survey figures. They are the bulk of what gets published as houseplant statistics, they usually trace back to a report a reader cannot open, and they do not help anyone keep a plant alive.

No survey run by this site. There is no panel here and no dataset, so producing one would mean inventing it.

No pet-poisoning counts. The NPDS report covers human exposures. Animal figures come from a different organization with different methodology, and putting them in the same table would imply a comparison that the two datasets do not support.

No rank positions from Table 20, for the extraction reason given above.

What is left is smaller than most pages of this kind, and every line of it can be checked.