I have one tree of Sambucus *****, the black elder. In my small garden, I have to keep hacking it back to prevent it from getting too big. It's much taller than the roof of my house, and if I let it, it would grow to around 10 metres (roughly 30ft) or more. I don't know how wide it would spread if I didn't hack it regularly, but it would be a fair distance - it's in a space which allows only for about 4 metres, and some of that is over my neighbour's fence. It produces lots of suckers which I have to remove frequently, and the roots travel a fair distance too - and nothing much else will grow where those roots are, not even mint!
Mine flowers nearly all year round, and I get plenty of fruit, so it must be self-pollinating. Even though I'm in the subtropics, I find it does tend to drop its leaves in winter, though is not fully deciduous.
Elder is one of the most useful herbs to have around. Aside from the culinary uses of both the flowers and the berries (use fully ripe berries only - green ones are toxic, and ripe berries are slightly toxic if eaten uncooked), it has multiple uses:
Flowers and ripe berries are used in a large range of dishes, both savoury and sweet. Add berries to salads, fruit drinks, muffins and jellies, pies and chutneys, desserts, or use to make wine. Add flower buds to flavour pickles, to apple pie, and use as a substitute for currants, or batter them as fritters. A wine is also made from the flowers. (I love elderberry jam, which tastes to me much like blackerry jam, and I love a syrup made from the flowers, not only as a cough medicine, but over ice cream!)
Grape-flavoured flowers are used to treat colds, hay fever, arthritis and sore throats, also used in potpourri, sleep pillows and infused as a skin softener. Flowers and berries are used to treat skin conditions, colds, flu and chest complaints. Berries are used to treat diarrhoea and haemorrhoids. Elderberry wine is used to treat night blindness. Elderflower tea is used for sleep problems, and is good for wrinkles, depression, fever, sunburn, burns, wounds, mouth ulcers, fluid retention, kidney stones, rheumatism, arthritis, gout, respiratory problems, hayfever, mild skin infections and freckles, or as an eye lotion. Berries are laxative, and the flowers will help stop diarrhoea.
An infusion of the leaves is insecticidal and repels mice, aphids and caterpillars, and can be applied as an infusion as a personal insect repellent. Wood can be used to make skewers, ornaments and small toys. Older branches yield a black dye, the leaves green, the berries blue or purple with alum mordant.
The American Elder (Sambucus canadensis) is smaller, growing to about 4 metres when cultivated and about 6 metres in the wild, is otherwise similar to S. *****, and is used in the same ways.