Scored for a wax plant, Hoya carnosa, at 22 °C and 50% humidity, a south sill at 13,000 lux comes back 100 out of 100. No window in our estimate gives a brighter spot, and the light there still reads just right. The score holds a great fit out to 2.1 metres, about seven feet, and drops to 68 ten centimetres further back.
Read on 14 October 2026, the answer box at the top of Google’s results says a south window can suit a hoya if the exposure is managed: a sheer curtain, a step back from the glass, or a spot at one side of the frame. It names six types as sun-tolerant. The pages below it split. Two gardening forums, one a 2012 Houzz thread, call south the window to want. Hoya Treasures and Plant Addicts allow it on conditions, a curtain or some room from the glass; Unsolicited Plant Talks keeps hoyas close in winter and further back in summer. A Reddit thread, seen only as a search snippet, says the poster’s hoyas won’t grow there.
Nobody says how far back. For a hoya, that’s the number that matters.
Great fit
This plant should be happy in this spot.
Just the right amount of light
Comfortable temperature
Humidity suits it
Airflow suits it
Is a south-facing window too much sun for a hoya?
No. The card above marks the light just right on the bare sill. A jade plant on the same sill still reads a little dim, and a golden pothos there reads too bright. A wax plant sits between them, inside its band with light to spare.
The published figures for a hoya, each in its source’s own unit, don’t settle it:
| Who publishes it | What it says a hoya needs | What the figure is |
|---|---|---|
| getgrowli.app | 4,000–8,000 lux | Growli's 'Bright Indirect' tier for hoya, the same band it prints for several other plants |
| getgrowli.app | 400–800 fc | The same tier, given in foot-candles |
| foliage-factory.com | approx. 10,000–20,000 lux | Care summary on the product page for Hoya carnosa 'Compacta', light at leaf level |
| foliage-factory.com | approx. 10,000–20,000 lux | Care summary on the product page for Hoya carnosa 'Tricolor' |
| extension.illinois.edu | 300 foot candles | Tier figure: wax plant is listed under High or Bright light, which the page sets at this level |
| mrec.ifas.ufl.edu | 125 foot-candles | Minimum for indoor spaces, for about 10 hours a day. Read from a web.archive.org snapshot of 13 August 2025; the live page now returns 404 |
| mrec.ifas.ufl.edu | 1500-2000 foot-candles | Light for commercial production, from the same archived page |
| bloomingexpert.com | 1,500–2,000 foot-candles | Second-hand: attributed to The Sill, whose hoya page now returns 404, so not checked at the original |
The two lux sources there can’t both be right about a south room. Growli’s whole band sits below the bottom of Foliage Factory’s, so the sill and the one-metre spot sit above one band and inside the other. Our band for this plant overlaps both: just right at 13,000 lux on the sill, and still just right at 6,015 lux, 2.1 metres back.
What a south sill can change is colour. The answer box warns that direct south light pushes many hoyas toward red or pink, a colour some growers chase on purpose, and the score doesn’t weigh it. Nor does it know where the plant came from. One carried off a dim shelf straight onto the glass can scorch or bleach, so the answer box’s week or two of gradual moving is worth doing even for a spot that scores 100.
How far back from a south window can a hoya go?
About seven feet. Here is one wax plant walked back from the same south glass, with two rows ten centimetres apart where it changes:
| Distance from the glass | Estimated light | What the light is doing | Verdict |
|---|---|---|---|
| 0.3 m, against the glass | 13,000 lux | Just the right amount of light | Great fit, 100/100 |
| 1 m back | 10,000 lux | Just the right amount of light | Great fit, 100/100 |
| 1.5 m back | 7,937 lux | Just the right amount of light | Great fit, 99/100 |
| 2.1 m back | 6,015 lux | Just the right amount of light | Great fit, 98/100 |
| 2.2 m back | 5,743 lux | A little dim, but workable | Worth a try, 68/100 |
| 3 m back | 3,969 lux | A little dim, but workable | Worth a try, 66/100 |
| 5 m back | 1,575 lux | Too dim here | Not the best fit right now, 47/100 |
From the sill to 2.1 metres the score slips two points. Between 2.1 and 2.2 it falls 30, from 98 to 68, as the light column turns from just right to a little dim. Warmth, humidity and airflow stay inside their bands on every row, so the whole drop is light. Past the step the slide is slow: 66 at three metres, 47 at five, where the light is marked too dim.
So pulling it back a little holds up, as long as a little means under two metres. Nobody in those results says where it ends, and in an open south room it ends at one spot on the floor. A ZZ plant at the same window changes verdict between the same two rows, in the other direction: that’s where it stops being flagged for too much light.
These lux numbers come from a calculation, not a meter: the window’s direction and the pot’s distance, on a cloudless day. None of them carries a season, so the winter-close, summer-back routine is one this page can’t test.
Does a sheer curtain help a hoya in a south window?
On the sill a hoya doesn’t need one, and a light sheer costs it little there. The 2.1 m row is still a great fit with under half the sill’s light, so a curtain that takes out less than half leaves a sill-side plant in the top band.
The trouble is stacking. The answer box offers its three fixes as alternatives, and a careful grower may use two. A pot already pulled back to 1.5 metres has 7,937 lux, and losing about a quarter of that puts it past the line, on the dim side with the 2.2 m row. A spot at the side of the frame is the same kind of cut. Neither curtains nor side positions are inputs to our scoring, so take a reading behind yours, at the pot.
Which hoyas can sit right on a south sill?
Five of the six the answer box calls sun-tolerant, going by our care data. Here are all six on the same sill:
| Hoya type | What our care data asks for | Verdict |
|---|---|---|
| Hoya ‘Sunrise’ | lots of bright, indirect light | Great fit, 100/100 |
| Hoya pubicalyx ‘Royal Hawaiian Purple’ | lots of bright, indirect light | Great fit, 100/100 |
| Hoya obovata | lots of bright, indirect light | Great fit, 100/100 |
| Hoya carnosa ‘Tricolor’ | lots of bright, indirect light | Great fit, 100/100 |
| Hoya carnosa ‘Compacta’ | lots of bright, indirect light | Great fit, 100/100 |
| Fishtail hoya (Hoya polyneura) | bright, indirect light | Worth a try, 68/100 |
The fishtail hoya is the exception. Our care data files Hoya polyneura a band lower, asking for bright, indirect light rather than lots of it, so the sill reads a bit bright and it scores 68. A metre back it’s a great fit.
So Hoya Treasures’ warning that not every variety belongs against the glass holds for one plant on this list. West glass gives far less floor: there a wax plant’s great-fit stretch ends between one metre and a metre and a half.
What else can flag a hoya on a south sill?
Warm air. Here a south sill behaves like a west one: the wax plant’s verdict turns between 28 and 29 °C, the same edge the west-window page finds on its own sill. Two metres in gives the same verdicts, so a hoya stalling on a hot sill needs cooler air.
Before you commit the spot
All of this assumes an open window on a clear day. An overhang, a tree, frosted glass or the building opposite pulls the step toward the glass by an amount nothing here can see. The south window guide covers what else wants the bare sill, and the free spot checker scores your own spot with local weather.
Published October 14, 2026
