Thanks! We do need a good thread about salvia propagation. The reference you shared is much appreciated, the author really got great results growing the plant indoors
Sadly I don't have a salvia plant now (the only one I had did not survive an unexpectedly long time away of the neglectful gardener), but I've grown it in the past. I cannot provide the precise technical details Seed Collector shared, but I thought I'd leave here a copy of my growing notes, so we start hosting information here in STS as well. These notes worked for me – maybe other gardeners have had different experiences, and if that is so, please do share to improve the thread!
Okay. if there was only one thing you could remember about growing Salvia D, make it this one:
the most common problem among beginning salvia gardeners is excess of attention. Too much water, too much hassle, too much misting, too much fertilizer... Sally is a very adaptable plant and does not require intensive care. Provided with acceptable initial conditions, salvia will only need some time to settle in her new environment, dig roots well and start bringing new shoots – as long as the gardener does not anticipate problems before there's any, and makes Sally's life hard when trying to fix them.
Sally's HomeHer sources are mysterious, and although she's been generally regarded as a cultivar, her origin is in the Oaxaca valleys in Mexico. Sally's natural habitat is rich in vegetation, rather humid, sheltered from sunlight thanks to the canopy. Soils are abundant in compost produced by plant decay, with good drainage. Air flow is gentle, and mean temperatures between 20-25ºC.
Most salvia cuttings, unless stated otherwise, will come from an environment similar to this: abundant filtered/indirect light, soil rich, spongy and moist, and medium-high relative humidity. However, adapting her to a much drier environment is perfectly feasible (ask changuar!) and will only require patience, time and making changes progressively.
The SoilYou can easily find many recipes for a good soil mix for salvia. It's not a particularly picky species as long as the soil drains well, breathes well and holds a good supply of organic matter. This is particularly true for cuttings in the process of rooting, and plants in the process of adaptation.
Adult plants can do well without any draining-ventilating agents in the substrate, but for a starting mix they are a good addition. The soil mix that worked for me was roughly 40% peat (sphagnum is a great option to include), 30-40% good compost, 10% worm castings or dung, and 10-20% perlite/vermiculite.
Salvia seems to like organic slow-release fertilizers. They highly decrease the risk of over-feeding and burn.
Water and HumidityNow we get to the serious stuff. Over-watering may be the #1 cause for trouble when growing salvia. Sally likes her soil moist, not dry, nor damp, and the more established the plant is, the more slightly moist the soil can be. So don't let the soil dry, and make sure it stays spongy. Watering slowly with a can, or even a mister, avoids compacting the soil and in the long run is much preferable to pouring a liter of water in one go. If soil is too packed, you can poke holes in it carefully with a large needle – and in case of emergency, when the roots are drowning, re-pot.
The amount of water salvia needs is closely related to the ambient humidity. The more humid, the less frequent the watering should be. The best way of judging is weighing the pot, or checking the soil. If it's still a little moist, more water is not necessary.
Over-watering is specially a problem in the case of rooting cuttings. You need to encourage root growth and strength, make the roots dig for water and not spoon feed them. The longer the plant takes to settle and develop, the longer she will stay more weak and vulnerable, so allow her to do her work.
And about misting, I think it's very overrated and seldom necessary. Daily misting (not to mention more than once-a-day misting) should only happen when the plant is dehydrated, and only for as long as she recovers. In my experience, raising ambient humidity temporarily when salvia is drought-stressed is much preferable to misting the plant often, since frequent misting creates a great environment for pathogens in the leaves. Fungi will thrive in the underside of wet leaves, and since Sally likes moderate-to-little air flow, nothing will bother them much until signs of rot are visible.
LightingSally can use a lot of light, as much as you can provide. Fluorescents are good since they barely emit any heat and do not make the air more dry, but HID lights will work well indoors too.
It's generally accepted that natural light is safer when filtered, or indirect. This does not mean that direct sunlight is harmful; it simply increases evaporation a lot and can make the plant dehydrated. But a salvia plant under direct sunlight will thrive perfectly fine when the humidity is kept stable and well. An improvised greenhouse or humidity dome will keep the leaves hydrated and help the plant deal with sun rays. However, I would avoid the intense noon sun unless the plants are really tough.
A note about bringing Sally out of the closet (aka Adaptation). Make it progressive, whether it is moving her out of a humidity dome, or moving her outdoors. Check the change in ambient conditions and take as long as the difference suggests. Think about all the time you will save when she's well used to your space, and don't rush it.
Diagnosing StuffDark, wilting leaf margins or tips are usually tissue rot - sign of overwatering, so either cut it down and/or make sure the soil is draining well. If you were misting her, stop and give her some cover instead.
When the dark tint appears in the main stem, chances are the plant has been long overwatered and has some degree of root rot. If the darkened areas grow, it may be time to rescue good, healthy cuttings and start over again. Roots with rot problems look yellow or dark, instead of the healthy normal white.
Burned leaves are caused by dry conditions, and turn the leaf tip and sides light brown and crumbly. To allow her to recover, raise ambient humidity and water if the soil is dry. Water slowly, so all the soil will soak uniformly before it drains.
Salvia leaves often curl when the environment becomes drier. This is not necessarily a problem, and it is expected when they are getting acclimated; in this case, new growth will appear as smaller, hardier leaves as a result of smaller vacuoles and hence smaller cell size.
Another reason why salvia leaves might curl is excess of some nutrients, so if the ambient humidity hasn't changed (and the plant hasn't been exposed to direct sunlight) and leaves are curling visibly, washing the roots with excess clean water and letting drain well can be helpful.
Clear, yellowing leaves suggest either overwatering (and nutrients flushed away), low temperatures, or lack of light. In the case of low temperatures, growth will come to a halt (and keep in mind that, as temperatures lower close to 5ºC, the plant will start suffering a good deal of stress). And in the case of poor lighting, the growth will also be elongated and the plant will start looking visibly weak.
Rooting cuttingsNo need to worry much about this step, IMO, since salvia cuttings are very easy to root when properly taken. Some people use water, others use soil, others use peat pellets, some use rooting hormone, others don't, and everyone swears by the method.
Personally I liked to put the cuttings immediately after taking them in a thin, small glass (or a glass tube) with distilled water, some root stimulator solution (1ml per liter) and a few drops of H2O2. Humidity dome, and fluorescent lights. As soon as they showed some root growth, easily before a week, I moved them into good, moist potting mix and back into the dome, at least for a few weeks.
...and that's all I could copy-paste from my notebook. Some day I'll get a new cutting and fill a few more pages.
Best Wishes,
Mandrake