I think it blooms on old wood, which is typical for plants that bloom in the spring. Prune it if you want a smaller, bushier plant. It is not necessary.

Interesting the very different experiences folks are having with this shrub. So I thought I would add my two cents from Toronto. I have two in my front garden (one of either side of the front walk), which is part sun and clay soil with lots of organic content. And they are excellent. I keep them relatively small with regular pinching, but I let them go a bit this Spring so I would get flowers and there are dozens on each shrub (still only about three inches across but growing everyday). They are bullet-proof and vigorous, for me, and their colour and form and highly dissected leaves are not easily replaceable. I have them with (among others) Liberty hosta, pincushion boxwood, Rozanne Geranium, Jack Frost Brunnera, Full Moon Maple, Krossa Regal and Blue Mammoth hostas, and Incrediball hydrangeas. I love the mix but it would be boring without the contrast this shrub brings, which makes everything around it pop. If I can figure out how to post pictures someday, I will.

yes i have seen this often with elderberry. even with well establishes patches with multiple plants, some of the berries will be great and some just dont quite make it. they take quite a while to get fully established before they produce a lot of flowers and berries. often they grow in huge patches with huge plants, you may want to add a couple of others of a similar variety to get better berries. and be patient, at least in my experience these take a couple of years to really get into their groove.

Elderflower Syrup 1 cup sugar juice of 1 lemon 1 cup water 8 cups elderflowers Make sure the flowers are young and white avoid any which are turning a creamy colour. Boil the sugar, lemon juice and water for 10 minutes, stirring until sugar is dissolved. Pour the syrup over the flowers. Cover with a clean cloth and leave overnight, then strain. Bring the liquid to the boil, remove from heat immediately and bottle. Store in the fridge for several months, discarding if it begins to bubble, ferment, or if any mould appears. Take 2 tablespoons twice a day for 6-8 weeks before hayfever season, or to treat a sinus problem. Add a little to fruit dishes, especially apples and pears, or fruit salads. Elderflower Cordial 1.5kg sugar 1 litre water 15 or more elderflower heads 2 oranges 2 lemons 2 limes 30g tartaric acid Dissolve the sugar in the water. Bring to the boil. Add flowers. Place fruit and tartaric acid in a bowl and pour over the syrup. Stir well and cover loosely. Leave for 24 hours. Strain. Bottle as desired. Store for up to 3 months in the fridge, or freeze. Elderflower Fritters (2) 200g flour (1 3/4 cups) 2 eggs 1/2 cup milk pinch salt 16 elderberry blossoms with stems sugar for dusting oil for frying With a whisk, mix the flour, eggs, salt, and milk into a pancake batter. Rinse elderberry blossoms several times, then pat dry with paper towel. Briefly dip the blossoms into the dough, and then deep fry until golden brown. Dust with sugar and serve. Elderflower Jelly 2kg apples, chopped whole, cores included 1.75 litres water 1kg sugar 6 large elderflowers 4 tablespoons lemon juice Put apples in a saucepan with the water. Bring to the boil and simmer until soft and pulpy, about 30 minutes. Line a colander with muslin, pour in the apple mixture and leave overnight to drain without disturbance. Next day, measure the liquid and add 2 cups of sugar to every 600ml of juice. Bring to the boil, adding the elderflowers tied in a piece of muslin. Boil steadily for 20 minutes until a little tested in cold water will set. Remove flowers after 5 minutes, or when the jelly is flavoured to your taste. At the last moment, skim off surface scum and stir in the lemon juice. Bottle and seal when cool. Elderflower Mousse 200g marscapone cheese 2 tablespoons commercial custard 125ml elderflower cordial 1 cup whipped cream Whisk all ingredients together to a mousse consistency. Elderflower and Orange Muffins 1 cup plain flour 3 teaspoons baking powder pinch salt 4 tablespoons sugar 1/2 cup fresh elderflowers 1 egg, beaten 1/4 cup milk 3 tablespoons melted butter, cooled 1/3 cup orange juice 1 teaspoon grated orange rind orange marmalade Sift flour with baking powder, salt and sugar, combine with elderflowers. Combine beaten egg, milk and butter. Add all at once to dry ingredients and stir lightly until blended. Quickly stir in orange juice and rind. Fill greased muffin tins to two-thirds full and bake at 190C for about 25 minutes. Serve hot with orange marmalade. If desired, drop a spoonful of orange marmalade on top of each muffin before baking.