How to Grow Elderberry from Seed
Elderberry seeds need the coldness of winter, or stratification, before they will germinate. Germination is tricky and plantings will sometimes produces nothing even though the same methods are used from year to year. Elderberry seeds have an extremely hard outer coat. This is a factor contributing to low germination. The most productive method is to mimic Nature's natural conditions of warm stratification for 2-3 months followed by cold stratification for 3 months. Winter weather conditions will play a big part in if a seed planting will be successful. I have planted seeds several times and some years I get elderberry plants and other years, typically warmer ones with less snowfall here in MO, I get nothing.
If you have any animals wandering around your property you should consider seed plot protection from animal disturbances. Cats, dogs, raccoons, armadillos, opossums, and chickens all seem to love scratching in freshly turned soil. Gather seeds after harvest and keep them in a safe place, or just leave outside and protected, until planting time.
When to Plant Elderberry Seeds
Plant seeds in late fall. Cover seeds with 1/4 inch of soil. Mist soil until soil is moist at a two inch depth. Water again if top inch of soil becomes dry before first frost. After frost water again ONLY if very dry periods occur. Watch for sprouting after temperatures remain at or above 68 degrees for 2-3 weeks. Caution, elderberry sprouts do not look like the typical elderberry, be careful not to mistake them for weeds and pull them up.
The very first set of leaves do not have the saw-tooth edges commonly associated with elderberry plants but are smooth and tear dropped as shown in some of the smallest ones in this plot of elderberry seed sprouting. The leaves develop the saw-tooth as they grow.
Why you may not be happy with Elderberries Planted from Seed
A cutting from a known elderberry plant will produce an elderberry plant with the same characteristics as the parent plant. An elderberry planted from seed will NOT have the same characteristics as the parent plant. Planting elderberries from seed produces plants that lack consistency. You will end up having plants with berries that are ripe at various times meaning you may pick one ripe cluster today and another cluster tomorrow and again the day after that. You will also likely have many clusters in which the berries do not all ripen at the same time, leaving you to try and pick out green berries before cooking with them.
Planting elderberries from seed may be the method you want to try if you want a cheap way to obtain many elderberry plants, are willing to take the chance that some or all of the plants may not be great producers and are patient enough to wait 2-3 years to find out. If time (you may not get them to germinate the first year) and a productive harvest is more important, it may be a much better idea for you to plant your elderberries from the cuttings of a known cultivar. One that has the properties that you desire, such as even ripening, large clusters, sweetness, or disease and pest resistance.
If you decide to grow your elderberries from seed do make sure to take your seeds from an exceptional elderberry plant, this should increase your chances of growing better elderberry plants from a seed.