What Succulents Actually Need
The light requirements for succulents are higher than for almost any other plant sold as a houseplant. The practical thresholds break down as follows.
To survive without etiolating, a succulent needs 3,000 to 5,000 lux for at least 6 hours per day. To stay compact and coloured as they would in nature, they need 10,000 to 30,000 lux for 6 to 8 hours, or 4 or more hours of direct indoor sun. To match their natural environment, that level of light is not achievable indoors without a grow light.
The indoor reality is that most succulents are operating at a significant light deficit. They survive because they store water and energy in their leaves, but they slowly degrade over months in insufficient light. The succulent you bought looking tight, colourful, and compact at the garden centre was grown outdoors or under high-intensity commercial lighting. Indoors, on a bookshelf or a coffee table, it begins to decline from the week it arrives.
Etiolation: The Most Common Indoor Succulent Problem
Etiolation is the technical term for what happens when a plant stretches toward light. In succulents, it looks like this: the stem extends upward or toward the window, with increasing gaps between leaves. Leaves become smaller, paler, and more spread apart. The tight, compact rosette form that makes succulents attractive disappears.
Etiolation is irreversible in the affected stem. That part of the plant will always be stretched. The fix is to cut the leggy growth back, propagate the healthy top, and put it in significantly more light. The cause is always insufficient light intensity, not watering or soil. No amount of adjusting watering frequency or repotting into cactus mix will stop a succulent from etiolating if it does not have enough light.
The problem is that etiolation happens slowly. A succulent moved from a garden centre display to a windowsill in January will look fine for a few weeks. By March it will have started to stretch. By June the rosette has opened up and the stem has elongated noticeably. By the following winter, the plant is unrecognisable from what was purchased. Most owners blame themselves for overwatering at this point, when the root cause was always light.
The Only Window That Works for Succulents Indoors
South-facing window, directly on the sill, no net curtain. This is the only position that comes close to what succulents need in the UK. In summer this provides 30,000 to 60,000 lux of direct sun on the sill. In winter it drops to 5,000 to 15,000 lux, which is at the low end of viable but better than any other window position available. Even a sheer net curtain can reduce incoming light by 30 to 50%, which takes a south window from borderline adequate to insufficient through winter.
West window as a second choice. A west window receives 20,000 to 50,000 lux of afternoon direct sun in summer. It is weaker in winter but usable, particularly for less demanding succulents. Position plants directly on the sill, not back on a shelf or table behind the window.
East window: at the borderline. East windows receive 15,000 to 35,000 lux of morning sun. Some succulents with lower light requirements, such as haworthia, gasteria, and aloe, handle east windows well. Cacti and most echeveria-type succulents need more light than a typical east window provides in the UK, particularly between October and March.
North window: not viable for any succulent long-term. North windows provide 500 to 2,000 lux, which is below what any sun-adapted succulent can use for sustained health. Succulents placed at a north window etiolate and eventually collapse. This is not a question of species selection; it is a question of whether sufficient light energy is reaching the plant at all.
Using a Grow Light for Succulents
If a south window is not available, a grow light is the most effective solution. For succulents specifically, the light needs to be full-spectrum LED, positioned 10 to 20cm above the plant canopy (significantly closer than for tropical houseplants), and running for 14 to 16 hours per day.
Succulents need more hours and closer placement than most tropical houseplants because their light requirement is so much higher. Tropical plants such as pothos and ferns can be maintained at 50 to 80cm from a grow light. Succulents need to be close to the source to receive enough intensity.
The combination of 14 or more hours at 10 to 15cm from a 30 to 50W full-spectrum LED replicates sufficient light for most succulents to remain compact. Running a grow light for 8 hours at 40cm is unlikely to prevent etiolation in a cactus or echeveria. The positioning and duration both matter.
Plug-in timers are essential for grow light setups. Running a grow light for the correct number of hours while the plant is unattended is what makes this a practical solution. Set the timer to run during daylight hours if possible, as plants respond to the total photoperiod rather than just intensity.
Winter and Succulents
Most succulents are adapted to seasonal light variation and will slow down naturally in winter even on a south window. This is normal behaviour, not a sign of a problem. They should be watered very infrequently in winter, once every 3 to 6 weeks for most species, because growth is nearly stopped and the roots will rot if kept in moist soil without active growth to use the water.
The problem is when succulents that spent summer on a south windowsill are moved to a shelf or coffee table in autumn to decorate the room for winter. This is where the irreversible etiolation damage typically begins. The succulent may look fine through November. By January it is visibly stretching. By the following summer, the damage is done. The solution is to keep succulents on the sill year-round, accepting that they are functional plants rather than seasonal decorations.
If you do want to use succulents as table decorations, limit their time off the windowsill to a few days at a time and return them to the sill between displays. Treat them like cut flowers in that context, not like plants that are living in the space.
FAQ
Why is my succulent growing tall and losing its compact shape?
It is etiolating due to insufficient light. The plant is stretching toward the nearest light source. This is irreversible in the stretched stems but can be stopped by moving the plant to a south-facing window directly on the sill. Propagate the compact top section by cutting it and letting it callous for a few days before replanting.
My succulent is on a south window and still etiolating in winter. What should I do?
South windows in UK winter provide significantly less light than summer. If etiolation starts in November to February despite a south window position, supplement with a grow light positioned 10 to 15cm above the plant for 14 to 16 hours per day. Most succulents will hold their compact form with this addition through winter.
Can succulents live in a north-facing flat?
Not without a grow light. A north window provides 500 to 2,000 lux, which is below the survival threshold for most succulents over more than a few weeks. If you want succulents in a north-facing home, a full-spectrum LED grow light running 14 to 16 hours per day is the realistic solution. Without one, choose plants adapted to dim light instead: ZZ plant, snake plant, or cast iron plant.
Do succulents change colour in more light?
Yes. Many succulents produce stress pigments (anthocyanins, carotenoids) in response to intense light, producing the red, orange, purple, and pink colouring that makes them attractive. A succulent with excellent light is often more colourful than the same plant in lower light, which tends toward plain green. This is one of the reasons grow lights can produce more vividly coloured succulents than window positions in the UK.
How do I know if my succulent is getting enough light without a meter?
The most reliable indicator is growth habit. If new growth is compact and the same size or larger than existing leaves, light is adequate. If new growth is smaller, paler, and further apart, light is insufficient. The shadow test also works: hold your hand 30cm above the plant at noon on a sunny day. A sharp, well-defined shadow means adequate direct light; a faint or absent shadow means the position is too dim for succulents.