So this...is a really big topic. Why? Because the genus is a really big one. Drosera currently contains more than 200 species worldwide, and they range from Arctic tundra and high mountain bogs and slopes to tropical grasslands, winter-wet near desert environments, fire-adapted regions and even cool rainforest streambanks. And their needs for the right conditions for a seed to sprout vary just as dramatically. No one group works quite the same, and no one species is necessarily the same even as its relatives or other species that grow in a similar environment. We can roughly divide the genus into a few groups though, so we'll start there...reminder though: there is never a guarantee with seeds, sometimes they just won't sprout for one reason or another. But the gamble is sometimes part of the intrigue.
There are some general rules that can be followed for most sundews however: moist soils appropriate for the species (peaty or sandy soils depending on habitat, sometimes but less often sphagnum), very bright light to full sun, and good airflow. Lose the former and the seeds don't sprout of course, and the latter two are necessary both for good growth and to prevent the bane of all seed-growers: botrytis, the gray mold that causes damping off. Etiolated seedlings are more at risk from this issue than healthy, pigment-rich seedlings with thick cell walls, and good airflow keeps those seedlings hardy while also making it harder for pathogens to establish.
Tropical Species
The easiest group to start with are the tropical and subtropical ever-growing species; coming from places where the conditions are suitable for growing most if not all year, not too cold, quite frequently very warm, these plants don't expect dry seasons, dormancies, stasis periods, or anything similar. So long as the seeds are either fresh or have been appropriately cold-stored in a dry fridge situation, all it takes is sowing them on an appropriate soil mix (most of them are happy on peat-based), keeping them at temperatures appropriate for the species, and waiting. Many species can start sprouting within a couple weeks although it's not uncommon for some to just take their time, up to a few months. Patience is a virtue, even the same batch of seeds may not all sprout simultaneously (a survival strategy, if something takes out the earliest sprouters, other seeds are still in reserve in the soil). Once sprouted, maintaining species-appropriate conditions is an obvious must, and feeding lightly can be beneficial IF you can avoid getting any fertilizer or food on the soil; as most of these species are fairly tolerant of little to no feeding if they're not catching things on their own, it's usually safe to wait until they're large enough to more easily apply food to their leaves only. Fertilizer or dead insects on the dirt provide a place for algae and fungus to grow which can threaten vulnerable seedlings.
Species that may fit this category include: Drosera spatulata, tokaiensis, oblanceolata, capillaris, brevifolia (in part at least; they can be kept evergrowing but will also react to drought or cold conditions by dying back to roots), aliciae, capensis, natalensis, nidiformis, affinis, madagascariensis, binata complex plants, felix, kaieteurensis, spiralis, graomogolensis, latifolia, tropical forms of anglica, rotundifolia, intermedia, and so on. D. regia is also in this category, but requires heavy feeding right from the start to do well.
Tropical Annuals
This category is very similar to the perennials, with the seeds just needing to be sown on appropriate soil and kept moist, in a warm, sunny environment. They typically sprout rapidly, though it can still sometimes take a couple months in some cases (particularly as they may like it warm, and cool conditions can slow sprouting). Where they differ though: they will need feeding, heavily. Most sundews can be fed rather sporadically in order to do okay, but with annuals built to live for only a short season before dying off they expect to start catching food quickly in order to grow quickly and flower, so providing dilute fertilizer to the leaves ONLY, or small insects, fish food flakes etc., is going to be more necessary if they’re not catching their own food. And as annuals usually can’t be propagated by any means other than seeds: you want healthy, big plants that will make a good seed set.
Species that may be in this category include: Drosera sessilifolia, burmannii, indica, serpens, finlaysoniana, hartmeyerorum, banksii, subtilis, and some people place certain forms of brevifolia here as well, along with the rest of the Arachnopus group related to indica.
Temperate Species
Temperate plants tend to require a little more starting preparation, as they set seeds usually in late summer to fall just before winter. It’s no good for seedlings to start growing right when frosts hit, so they are built to remain dormant until cold weather passes. These seeds need a cold stratification period therefore to break down growth inhibitors and allow germination. This can be achieved by sowing the seeds on the soil surface of a bog garden just before or during winter (or at least a few weeks before warm weather will begin), or on a pot surface and then placed in a bag in the fridge for typically and obligate 4 weeks (linearis and other very cold-adapted species may need up to 8), more if you just need that time to prep a space, before setting that pot in a warm, sunny location. Best not to leave pots of seeds outdoors however as they are more at risk of drying out, tipping over, wind and rain removing seeds from the pots, etc. Or, you can take the route I do: wrap the seeds in a small piece of paper towel that’s moistened down and put into a sealed baggie, and place that in the fridge for the necessary period. It saves space and works just as well, and the seeds can then be wiped or washed off into the intended pot afterward. After this, they behave as the evergreen tropicals do: a couple weeks to a month or two to germinate, then give good light and feed carefully if you can to speed up growth (especially for linearis) before they go dormant for their first winter. Unlike American pitcher plants or flytraps, sundews are obligate dormancy required from the start, there’s no skipping that cycle unless you want weak plants that may rapidly die off.
Species in this group include the temperate forms of Drosera anglica, rotundifolia, intermedia, filiformis, tracyi, and I have not found as much info on these species but I would assume similar behaviors needed: arcturi, murfetii, stenopetala, and uniflora.
Petiolaris Sundews
The woolly sundew group from Australia likes it HOT, and the seeds do too. The best success will be had with seeds that are fresh and sown as soon as possible after they ripen, and then keeping that pot in very swelteringly warm conditions with moderate to high humidity (and airflow is very important here). Seedlings start out incredibly small, and great care must be taken if feeding them to get the food only on the leaves otherwise algae will easily smother them. If you can’t get very fresh seeds, that’s where things get a little trickier and there’s a lot of conflicting information. Some people recommend just waiting a few extra months for them to sprout, others will use smoke treatment or gibberellic acid in low concentrations to soak the seeds and remove inhibitors that are believed to build up in the seeds over time to prevent them from sprouting in a dry season (usually around 500 ppm for 24-48 hours). Others recommend scarification, lightly rubbing the seeds between something slightly rough like fine sandpaper to remove a part of the outer coat to let water in. Whether any of these techniques work to enhance germination…is still rather in question, and may actually vary between species as hairier species expect slightly different (drier, usually) environments and stronger seasonality than more swamp-adapted types with more glabrous leaves. Species in this category include Drosera paradoxa, lanata, falconeri, ordensis, kenneallyi, petiolaris, dilatatopetiolaris, derbyensis, broomensis, and the various undescribed taxa and hybrids out there as well.
Winter Growing Sundews
In this category I’m speaking about species such as the South African large-flowered plants, as tuberous and pygmies are in a bit of a different mess on their own. Species with thickened roots that grow throughout cool winter conditions and flower and set seed right before summer hits have seeds that typically can be just sown on soil and kept moist, however you may find they won’t germinate one way or the other until conditions are cool again, reflecting the onset of winter. A hot dry period first, ie. a hot stratification, may benefit them and boost germination, but otherwise they will only begin growing come winter either way. Once the seedlings sprout, they will need heavy feeding to build up root reserves before the next winter season, and must be kept cool with shorter light periods or they will enter dormancy too early. Many species also may not appreciate being kept too wet, but just moist or even drying a touch between waterings otherwise they are at risk of rot. Species here include D. cistiflora, trinervia, pauciflora, coccipetala, zeyheri, and I will also put in here species that grow year round if conditions remain cool such as hilaris, ericgreenii, ramentacea, xerophila as they need similar sprouting conditions and relatively dry soils, and will enter a dormant-like state if it gets too hot.
Winter Annuals
There is really only one species that I can think of right now that fits this category, and that’s D. glanduligera. This funky little annual likes it best when the seeds are sown during the warmer summer months and left under a hot, dry stratification state for a little while, and then when it gets cool again adding moisture and keeping the sandy soil damp. Seedlings start out small, and MUST be fed frequently and the temperatures kept fairly cool, below 60 degrees Fahrenheit best. Shortened daylengths may also benefit keeping them around longer, because they need to feed and grow rapidly and begin blooming as once it begins brightening and the temperatures start to warm, they will quickly bolt to bloom one way or another and die off, and seeds are the only way to propagate them.
Tuberous and Pygmy Sundews
I group these two oddballs together because they both have plants that fit a variety of similar seed-treatment needs: there are species that are laughably easy to sprout, those that need a little bit of encouragement, and then some that either have really tricky needs to trigger germination or are just hard to get seeds from at all. The easiest species are those that flower and set seeds readily, and grow in a wide range of habitats and as such don’t really need any special care. The seeds may not be many in number when produced, but are made fairly regularly and just need to be sown on moist soil in cool conditions and given time to sprout. Drosera omissa, lunata, hookeri, gunniana, and more summer- or ever-growing temperate forms of auriculata and peltata may be included in this group (though most of the tuberous species will eventually fall into a winter-growing habit, no matter when the seeds sprout). The seedlings may need to be fed well particularly with tuberous sundews to bulk up storage organs, but are otherwise fairly straightforward. Some species need more finesse to get seeds or get them to sprout. Drosera platystigma, menziesii, stolonifera, rupicola, and some others may set seeds fairly readily, or need cross-pollination but then usually set good numbers, but require exposure to hot stratification before sprouting. Sowing the seeds on the soil surface and then leaving them warm and dry over summer allows them to prime for the seasons before sprouting in winter, and then keeping them cool, bright with short daylengths, and well-fed allows them to bulk up before going dormant. Many of the other tuberous species definitely need cross-pollination and are just sometimes finicky to set seeds, and a handful of pygmy sundews are similar, and the seeds are a bit enigmatic in terms of figuring out what is needed to germinate them. Several seasons of hot-and-cold cycling, smoke treatment, or dilute gibberellic acid treatment may be needed to break down inhibitors before they will sprout (scarification of larger seeds between sandpaper layers may provide similar preparation), and in particular a lot of rosetted tuberous species and pygmy sundews may resist germination overall no matter what is done, so patience and a willingness to try multiple techniques may be needed. And, there is more than a handful of species that just plain almost never set seeds period, so what their species need in order to germinate remains rather unknown just because there are few chances to try (squamosa, erythrorhiza, aberrans, whittakeri etc. may be examples; they flower regularly but rarely do seeds follow).
The Queensland Sisters
This group I put last, not because they’re necessarily hard to germinate or grow on afterward…but just because seeds are a nearly unheard of thing for most people. Growing in nearly permanently wet, humid, shady conditions, they have behaviors similar but in a darker habitat to the other tropical evergreen perennials. Flowers are sent up on happy plants…but even in the rare cases one gets to cross-pollinate them, it’s just rare for any seeds to be produced. And if produced, each flower may only make one to a handful of seeds. Vegetative propagation is their primary means of spreading, and overall just the easiest method to focus on. On the off chance you are a very lucky person and get seedpods on D. adelae, prolifera, schizandra, or buubugujin when it eventually enters cultivation though, sow them immediately on a moist loose peat or milled sphagnum soil, keep moist, fairly cool, somewhat shady, and humid, but with VERY good airflow as the conditions they like growing in otherwise is an absolute magnet to botrytis. If sprouts occur, feed very lightly if at all and be patient with their growing.
Now, with this genus there are often nuances for various different species and certainly far too many to address sufficiently individually, so if there is something I seem to have missed here…well, just visit the Database on the website instead as there each species will have its own page and individual care needs listed (and if you’re looking for a species I haven’t posted up yet, send me a message and I may be able to work it in). Hopefully though, this might provide a brief overall start to the various groups, with some pointers for the easier species to look for to start off with.