Q: For six years I’ve had a pair of hydrangea bushes that hardly bloom. When I bought them, they had gorgeous globes of blue flowers. I prune them by about a third every year in late summer. Once I tried a special fertilizer recommended by my nursery, and I didn’t get any flowers the following year. Is there some trick? — Esther Kitchen, Millersburg, Pa.
A: You are pruning them back way too much. You have the old-fashioned Hydrangea macrophylla, whose flowers come from buds along stems that developed the previous summer, and you are cutting them off. The simplest rule for pruning hydrangeas is: Don’t. Most hydrangeas grow well with no pruning at all, and basically you should cut only enough stem to use the flowers in arrangements. The plants will grow a little bigger each season, so if you need to keep your hydrangeas in bounds, you will need to prune them a bit each year. But that doesn’t mean a radical haircut with hedge clippers. The best way to prune hydrangeas and still get flowers is to cut some of the oldest stems at ground level — about a quarter of them — during the dormant season. (Later is better because sometimes extreme cold or ice will damage some of the stems, and those you should cut out first.) Then shorten remaining stems by just a few inches, cutting back two or three leaf nodes because the flowers form on new growth that comes from year-old wood. You will end up with a natural-looking plant about 4 to 6 feet tall. If that is still too tall, consider a variety that is naturally shorter. There are hundreds of varieties of H. macrophylla. Most grow in the 4- to 6-foot range, but there are a few that are typically 3 to 4 feet. Shortest of all is ‘Pia,’ which matures at just 2 to 3 feet. It’s surprising that the nursery recommended fertilizer, which encourages foliage at the expense of flowers. Generally all hydrangeas need is a mulch of shredded leaves or well-composted bark, which also conserves soil moisture. Give them that, prune judiciously late in the dormant season, and you should soon have a fine crop of flowers.