Salvia can be cultivated using hydroponics. I have four mother plants growing this way. I started it just as an experiment (started Jan 2002). I'm not an expert in the art. In fact, I nearly killed them in their early stages, - almost certainly due to overfeeding, but they recovered after I refilled the tank with fresh water, and have been doing well since adding reduced amounts of fertiliser.
My set up has the plants growing in rock wool. The pots are in a tank part filled with water. The bottom of the pots stand above the water line. The pots' water supply is via a hose connected to an underwater aquarium pump. The single connection from the pump is split four ways, - a line to each of the plants [...^] A timer switch ensures that the pump is off for 15 minutes every hour (another controls the lights, as per section on artificial lighting)
Results over all have been no better than growing in soil to be honest, but good enough and this could simply be my lack of expertise. For example, the amount of feed I add to the water is mostly guesswork (I possibly err on the side of caution, but I'm reluctant to put too much in), and there may be more optimum on/off timer ratios I could use on the pump.
Accounts from readers with more experience are invited.