When does autumn start in 2026?

• 2 min reading time

Autumn starts on 1 September if you follow the meteorological calendar, and on 23 September 2026 if you follow the astronomical one. Both are correct, they just measure different things. That is why weather forecasters talk about autumn from the first of the month while your calendar app waits another three weeks.

The two dates explained

Meteorological autumn always runs from 1 September to 30 November. It splits the year into four tidy three-month blocks, which makes it easy to compare weather data between years. The date never moves.

Astronomical autumn begins at the September equinox, the moment the sun crosses the celestial equator and day and night are close to equal length. In 2026 that falls on 23 September. It shifts by a few hours each year, which is why the equinox lands on the 22nd or the 23rd depending on the year.

What changes indoors

The practical shift is light. From late September the days shorten quickly, and rooms that were bright all summer start getting a few hours of weak light instead. Houseplants notice this before you do. Growth slows, and the amount of water they need drops with it.

Heating is the other change. Radiators dry the air out, which is hard on tropical plants but barely registers for succulents and cacti. Closed terrariums are largely unaffected, since the sealed glass keeps its own humidity regardless of what the central heating is doing.

Getting your plants through it

Three adjustments cover most of it:

• Water less. Cut back roughly by half from October, and check the soil rather than sticking to a schedule.
• Move plants closer to the window as the light drops, but keep them off cold sills at night.
• Stop feeding until spring. Plants are not growing much, so extra nutrients just sit in the soil.

Autumn is also when indoor gardening picks up again, simply because there is less to do outside. A DIY terrarium kit is a reasonable way to spend a wet weekend, and a closed bottle garden needs almost no attention through the darker months. If your rooms lose most of their daylight in winter, artificial plants keep the green without the struggle. For terrariums that have been running a season or two, a refill kit and a few basic plant care tools are usually all they need before winter.

In short

If you want one date, use 1 September. If you want the astronomical one, autumn 2026 begins on 23 September. Either way, the useful signal is the light, and that is what your plants will respond to first.

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