What is the most reliable way to root basil and rosemary cuttings?

The two behave very differently and treating them the same is why one usually fails.

Basil is soft-stemmed and roots in water in about a week, often faster. Take a fifteen-centimetre shoot from a non-flowering stem, cut just below a node, strip the lower leaves so nothing sits underwater, and stand it in a glass on a bright windowsill out of direct sun. Change the water every two days — stagnant water is the main cause of failure. Once roots reach two to three centimetres, pot up promptly; water roots are structurally different from soil roots and a cutting left too long in water struggles to transition.

Rosemary is woody and rots readily in water. Take semi-ripe cuttings in late summer: this year's growth that has firmed at the base but is still flexible at the tip, around ten centimetres. Strip the lower two thirds, dip in rooting hormone, and insert into a gritty mix of equal parts perlite and compost. Cover with a clear bag or propagator to hold humidity, keep out of direct sun, and be patient — six to eight weeks is normal. Tug gently to test; resistance means roots.

For both, take more cuttings than you need. A fifty per cent strike rate is normal and taking six costs nothing.

Two things improve the odds across the board. Use clean, sharp secateurs or a blade rather than scissors, which crush the vascular tissue. And take cuttings in the morning when the parent plant is fully turgid rather than in the afternoon heat.

Pinch the growing tip once the young plant is established. That is what produces a bushy herb rather than a single leggy stem.