Why is my begonia dropping leaves after bringing it indoors?

What's likely going on

From the photo, the plant still has lots of foliage, but some stems look a bit droopy and some leaves are losing color. When a begonia that was happy outside is brought indoors, it goes through environmental shock:

• Light suddenly changed – outdoors it probably had brighter, more even light. Indoors, the light is weaker and comes from one direction, which can cause leaf yellowing and drop.
• Humidity and temperature shifted – indoor air (especially with AC or heat) is drier and can stress the plant.
• Watering pattern changed – it’s easy to overwater once it’s inside, because the soil dries more slowly, leading to root stress and dropping leaves. Underwatering can cause similar drooping, so the soil needs checking.

The leaf fall is the plant trying to adjust to its new conditions rather than a single disease.

What to do

1. Check the soil
   Push a finger a few cm into the pot. If it’s very wet and heavy, let it dry out before watering again. If it’s completely dry and pulling from the sides, give a thorough drink, then drain well.

2. Improve the light
   Place the begonia in bright, indirect light near a window, but not in harsh midday sun that can scorch leaves. Rotate the pot weekly so it doesn’t lean.

3. Tidy the plant
   Snip off any fully yellow, brown, or mushy leaves and stems with clean scissors. This helps it redirect energy to healthy growth.

4. Stabilize its environment
   Keep it away from heaters, AC vents, and cold drafts. If the air is very dry, a tray of water with pebbles under the pot (pot sitting on the stones, not in the water) can gently raise humidity.

5. Water correctly going forward
   For most indoor begonias, water when the top 2–3 cm of soil feel dry, then empty any saucer so it doesn’t sit in water.

How to prevent it

• Move outdoor plants indoors gradually over 1–2 weeks, starting in bright shade, then indoors.
• Use a well‑draining potting mix and a pot with drainage holes.
• Keep a fairly constant spot indoors rather than moving it often.

When to worry

• If stems near the soil turn mushy, black, or collapse, root rot may be setting in—repot into fresh, well‑draining soil, trimming off rotten roots.
• If you see sticky residue, webbing, or lots of tiny insects on leaves, treat for pests (start with a gentle soap spray).
• If almost all leaves drop and new growth doesn’t appear within a month or two, reassess light and watering; the roots may be badly damaged.