Most salvias grow readily from seed, but germination of some species can be improved by several techniques. Temperature, moisture and light are the three fundamental factors.
All seeds have a temperature range for optimal germination. For salvias, as for most garden seeds, daytime temperatures in the low 20s (C) are good. Just avoiding hot and cold weather is generally enough.
Beyond that, two primary aspects of salvia seed germination are constant moisture, and light. If you’ve soaked chia (Salvia hispanica) seeds you’ll be familiar with the mucilage they secrete. This is the first aspect of gemination with most salvias; seeds sitting on the soil surface absorb rain water and surround themselves with a protective mucilage coat which also binds them to the soil.
Salvia seeds also require light to germinate. Unlike standard sowing techniques, salvia seed needs to be scattered on the surface of the soil and exposed to daylight. This is counter-intuitive to the usual ‘sow at a depth twice the seed diameter’ advice, but for salvias you don’t drill a row, sow and cover, you just scatter on the surface. By the way, it’s worth checking other seed, you might be amazed how your poor lettuce or basil germination suddenly becomes 90% with surface scattering.
To bring these conditions together, I sow saliva seed before a rainy spell, in flats filled with seed sowing mix (sieved potting mix) on a seed raising bench; a raised platform with a shade cloth cover. While you can water regularly, choosing a rainy spell really does seem to give optimal results. I try to set up the seeds the day before rain is forecast.
Dormancy
Some salvia seed can also have inherent dormancy. Species that live in harsh conditions are at advantage if their seeds resist germination at the first rain event, and wait for conditions that are likely to allow continued survival. In mediterranean climates favourable conditions are often Autumn rains following Summer fire, and dormancy can be broken in many species by exposure to smoke. On the other extreme, in climates with freezing Winters, seed that falls in Autumn is at advantage if it resists germination until Spring, and in this case the stimulus for breaking dormancy is a period of chilling. I have tested both dormancy breakers with small numbers of seeds.
A converse aspect of dormancy is that seeds can require a storage period. Anecdotally it seems that seed taken directly from the plant and sown can have poor germination, while the same batch germinates well after some months of storage.
Freezing
The simplest treatment was freezing, and for me it had no effect in a likely species. My Salvia azurea plants produce seed in Autumn, and I guessed that, as it is from a cold Winter climate and the foliage dies right down even here, freezing the seed might promote germination. Consequently I counted out two lots of 20 seeds, kept one lot in the fridge (with all my seeds), and put the other in the freezer for two months, then the fridge. I sowed both in Spring (before rain). Two of the frozen seeds germinated, compared with 4 of the refrigerated seeds. The numbers are small, but freezing didn’t increase germination.
Smoking
Smoke treatment is more complicated. There is a range of smoke treatments available commercially, but I went for home made, as I have a food smoker. It’s a metal box, like a large shoe box, with a raised base that can sit above a bowl of spirit, and a rack inside. You load one end with wood chips, sit them over the burning spirit, and let them smoulder in the closed box. I used one hot smoking to infuse a ramekin of water. The wood chips burnt completely down and the water became brown and strongly scented. I then used the smoked water to soak seed overnight by sitting them on paper towel wet with smoked water.
I also tried dry smoking, by putting the seed in foil boats or ceramic spoons on the smoker rack and carefully lighting chips so that they smouldered from the ends, this time without the spirit fire so that the seeds weren’t appreciably heated. The smoke was enough to leave a brown film on the spoons. Smoking took about an hour.
I sowed dry smoked seed using my standard method. For smoked water treated seeds I transferred them from the wet paper towel to the sowing medium. I timed sowing to precede a couple of days of rain.
The seeds I selected for smoking were three likely mediterranean contenders, S. aurita from South Africa, S. leucophylla from California, and S. canariensis from the Canary Islands. I sowed 20 of control and each treatment.
The table shows that all three germinated better with smoke treatment, and that dry smoke was better than, or as good as, smoked water.
| untreated | Dry smoke | Smoked water | |
| aurita | 0 | 14 | 4 |
| leucophylla | 0 | 11 | 7 |
| canariensis | 1 | 6 | 5 |