How do you propagate an orchid from keiki?

Keiki are little offshoots that grow on the orchid's stem, and when they have their own roots (usually at least a couple of centimeters long) you can gently detach them and put them in a small pot with bark or orchid substrate. The important thing is to keep it moist but not waterlogged, and give it air and indirect light until it roots well. After a few weeks it should start to stabilize, and when you see new leaves growing that means it's taking hold.

It's not exactly straightforward to detach a keiki and expect it to survive right away. The thing people don't often get told is that before you detach the little shoot, you need to make sure it has decent roots of its own - not just a couple of centimeters, but preferably four or five, and they should already be somewhat developed and whitish or greenish in color. If you detach it too early when the roots are just starting, it risks rotting or simply won't take.

Once you have the keiki with good roots, then yes, you detach it with a clean cut as close as possible to the base. Here's the critical point that people overlook: don't put it straight into bark or normal orchid substrate like nothing happened. Keikis are still fragile, they've lost the support of the mother plant, and the rot risk is super high if you water it too much right away. I prefer putting it in a very aerated mix, almost pure sphagnum moss but not packed down, in a small pot with drainage holes. Keep the substrate slightly moist but not waterlogged, and most importantly put the pot somewhere with high humidity - if you can use a small terrarium or even just a transparent bag with a few air holes.

The roots will keep developing over the following weeks, and after a couple of months when you see the keiki pushing out new leaves and the roots are pretty robust, then you can gradually move it toward a more standard orchid substrate. Patience: that's the real secret here.