Hi all... new here and I know this post is a few months old but I thought I'd chime in, as I know folks searching on Google will be harvesting answers from old threads like this, for years to come. I do it every day and am always grateful when I can find some semblance if an answer somewhere.
I've been growing and loving fragrant indoor plants for 2 decades... I don't have a lot of experience with Heliotrope but I think I can offer some limited advice that might be helpful re: growing from seed...
About 15 years ago I was visiting a large nursery and I followed a heavenly scent, which brought me to full hanging basket of purple heliotrope. For years I have believed it to be marine heliotrope (may have just assumed, via pictures online). Anyway, I grew it indoors for about a month, and life got in the way at the time, and I let it fade and die. I was so sad and missed that beautiful scent.
So, 5 or so years later, I purchased marine heliotrope seeds on EBay and this is what I remember... the seeds are TINY, I believe you have to provide the roots heat from below, which I did, I also provided them with full spectrum artficial lights (i vaguely remember that they needed light to germinate, as most tiny seeds do) hundreds of tiny little green seedlings germinated. I took the clear dome off and lightly misted them for a couple of days, anxious to see their first set of true leaves appear, but when I went to check on them, on day 3, the entire crop of seedlings had been very quickly wiped out by fungal infection.
So, I'm not sure if the bush kind, mentioned above, has seeds just as small, but I would have 3 suggestions, based upon my experience, if anyone were going to try to grow these from seed.
1. Either use a mixture of vermiculite and perlite to sow your seeds, which will retain humidity for the tender seedlings while also providing drainage and a "close to" sterile environment. Or bake the soil you plan to use in your oven, at 350F for an hour. Let it cool off after and use that to sow your seeds on top of , to cut down on the risk of your tiny seedlings damping off.
2. Use several smaller pots, under a humidity dome, to sow your seeds. That way, you will have a chance to catch any problems early and remove problem seedlings before it spreads to them all. They are so tiny, and grow so slowly at first, the chance of there being a problem in that time, that wipes out all of your seedlings in the blink of an eye, is very high if you don't take this precaution. You may not even want to place the pots under the same dome, if space and supplies allow for that.
3. My little seedlings all germinated in a thick little patch... I didn't have much experience back then and sprinkled them too densely. I think the lack of spacing contributed to a lack of air movement and helped the fungal infection to spread so quickly, so if I were to do it again (and I will be doing it again soon) I would mix the seeds together with a handful of course sand... maybe 5-10 parts sand to 1 part seed, and I would sprinkle the seed that way.
Anyway, I hope this helps someone or "someones" out there on the internets! 🤞
