Bold, Big & Beautiful
Common Name: mophead, bigleaf hydrangea, lacecap hydrangea
Botanical Name: Hydrangea macrophylla
Form: broad spreading, rounded
Plant Type: deciduous shrub
Mature Size: 3 to 4 ft tall to 3 to 6 ft wide
Origin: Europe, Asia, Mexico, North, Central & South America
Hardiness Zone: 6 to 9
Foliage: 4-8” long, simple, serrated, shiny, dark green
Flowers: July to August, pink or blue depending on soil pH, clusters (corymbs) of showy florets surrounded by pink or blue, four petals,
Fruit: a capsule containing several seeds
Stems: two leaves are opposite each other on woody stems
Exposure: part shade, avoid hot afternoon sun
Soil: moist well drained, does not like dry soil, organic rich loam,
Uses: mixed shrub border, woodland gardens, accent, foundation, informal hedge, cottage gardens, cut and dried flowers
Invasive Tendencies: none
Tolerates: shady locations with moist soils
Pruning: needs little pruning
Problems: powdery mildew, hydrangea rust
Bigleaf hydrangeas are loved and admired for their gorgeous clusters of their long-lasting pink or blue flowers. These bold shrubs bring dull gardens to life with their coarse texture, round form and persistent flowers. Even without their flowers, they have multiple uses in the garden. Their large, deep green, shiny serrated leaves provide the perfect backdrop for smaller shrubs, perennials and annuals. Hydrangeas also add some sassy bulk to mixed borders, provide a multistory transition from trees to smaller plants and they make an impressive jaw-dropping hedge.
Mopheads & Lacecaps
There are two types of bigleaf hydrangeas: mopheads (hortensia) and lacecaps. The only difference between the two are their flowers. Mopheads have round flower clusters (corymbs), comprised of colourful sepals – not petals. In the centre of the sepals is the true flower, a tiny star shaped blossom. Lacecaps are more delicate as their name implies. Their corymbs are flat with a couple of rows of pink or blue sterile sepals surrounding a mass of small fertile flowers. The actual flowers only blossom for a few weeks in the summer, but the colourful sepals remain throughout the winter.
Flower Colour & Soil pH
The acidity of the soil is responsible for flower colour, except for white varieties are not affected by soil pH. Flowers turn shades of blue and purple in acidic soils and become pink where the soil is alkaline. Note that to maintain the colour you have chosen, it is an ongoing and annual process as the soil converts back to its natural pH.
Pink to Blue: To turn pink hydrangeas blue, add organic material to the soil to make it more acidic. Mix in compost, pine needles and coffee grounds. Alternately mix in 1 tbsp of aluminum sulfate into a gallon of water in the fall and throughout the growing season. Water plants well first before applying and don’t increase the dosage as too much can burn the roots.
Blue to Pink: To turn blue hydrangeas pink, mix in ½ cup of Dolopril lime around the dripline of the plant every two months throughout the growing season and into autumn.
The Trouble with Hydrangeas
Hydrangeas are considered an easy, low maintenance plant – but only if they are in the correct location. Avoid placing them where they receive hot afternoon summer sun, especially combined with dry soil, as they will quickly wilt and decline.
Hydrangeas get a bad rap for getting too large, too fast, and as a result they suffer the indignities of being chopped down to nothing with no flowers to boot. Bigleaf hydrangeas’ girth is about 6 feet, so give them room to grow. No matter how often they are cut back, these plucky hydrangeas revert to their natural size. Note that severely pruned hydrangeas fail to have a good show of flowers, if any at all. If you have one that’s too big for its space, consider transplanting it to another location in the garden. For a replacement, there are many smaller and exciting new cultivars and hybrids available.
Dry soil is another no-no. Their name says it all. The word ‘hydrangea’ is derived from hyros, the Greek word for water. Without adequate soil moisture, they wilt - then collapse. They aren’t good in sandy soil as the water drains too quickly, however an organic rich soil is ideal as it retains the moisture. A 3-inch layer of mulch placed around the plant and on top of the soil is essential to prevent soil moisture from evaporating.
Pruning Mophead & Lacecap Hydrangeas
It is recommended to prune mophead and lacecap hydrangeas right after they finish flowering. That advice is confusing since the ‘flower heads’ remain on the plant throughout the winter. But those flower heads are not the ‘flowers’, they are sepals. The actual flowers sit in the centre of four coloured sepals. Cut the plant back once those wee flowers fade no later than the end of July. Don’t cut back hydrangea stems too far back as they won’t flower the following year. Cut the stems back to the first to third set of fat healthy buds – no more. Cutting stems back any later will remove future flowers.
In fall to early spring, it’s fine to remove just their flowers. Just cut off the blossom to the closest set of two healthy buds, no lower. Also remove dead, diseased, spindly, broken and old stems that no longer flower. To rejuvenate old, neglected hydrangeas, cut back all the stems to their base. They won’t flower the following year, but they should the next.
Reason why hydrangeas fail to flower: