Tree peonies and their kin

The natural elements can be cruel. The fabulous, 10-inch (25-cm) blossoms on my mauve tree peony (Paeonia suffruticosa, Zone 5) are all smashed up, the result of an unpredicted heavy rain one recent evening. That was certainly a low blow to a gardener who, with a little advance notice, would gladly have stood there holding an umbrella over the blooms during the deluge. That would be easy gratitude for the pleasure they give me.

The flowers of tree peonies are startling huge and beautiful (and some are deeply scented), and their foliage remains attractive all season. The Irish gardener and horticultural writer William Robinson (1838-1935) grew many tree peonies, and suggested spotting them throughout perennial borders, or giving them a display bed of their own with a low ruffle of long-blooming perennials such as the little Carpathian bellflower (Campanula carpatica, Zone 3) surrounding them.

Tree peonies are small shrubs with woody stems that remain through winter. They’re usually self-supporting, although it’s been my experience that they get a bit lax and floppy when grown in low light and sometimes require staking. Tree peonies will flower in part shade, but more blossoms and stiffer stems are produced in sunny locations. They’re grafted on rootstocks of species herbaceous peonies, and occasionally the rootstock sends up a stem with leaves noticeably different from the tree peony. Cut out any rogue stems coming from below ground as low as possible, otherwise they can overwhelm the grafted plant above.

I also have several herbaceous peonies inherited with my garden, including double pink ‘Sarah Bernhardt’ and single white ‘Jan Van Leeuwen’ with a centre of thick yellow stamens (and delicious lemon scent). When the flowers are finished, their foliage takes up more space than I want to give them. I know the leaves are working all summer to store energy for next year’s flowers, but I don’t think it hurts to eliminate up to 25 per cent of the stems, cutting from the outer edges of the plant, to reduce its bulk. So far this method of controlling their size hasn’t reduced flowering.

A new category is intersectional peonies (sometimes referred to as Itoh peonies), the result of crossing herbaceous and tree peonies. Intersectional peonies die to the ground in winter, but their flowers and foliage are quite like tree peonies, and colour choices include yellow, unknown in herbaceous peonies. This innovative breed of peony strikes me as a good opportunity to begin a new collection (My acquisitive spirit perks up!), and I think they would make a superb double-bordered peony walk. Once the flowers are finished, the ornamental foliage would continue to enhance both sides of a pathway for the rest of the growing season. This seems the ideal combination of peony attributes, and my compliments to the clever plant breeder who thought of this.

Time to prune lilacs

The lilacs have been terrific this year, their flowers lasting so well in the cool, moist spring conditions. Lilac season begins with the early Syringa x hyacinthiflora cultivars, including Canadian-bred lavender-pink ‘Asessippi’ and violet-purple ‘Pocahontas’. These are followed by the S. vulgaris French hybrids, a large category with familiar named plants like purple ‘Agincourt Beauty’ and white ‘Madame Lemoine’. The latest to flower are the Preston lilacs (S. x prestoniae), another group of plants bred in Canada, and including my bright pink ‘Miss Canada’, currently blooming in the front garden. The Preston lilacs are particularly vigorous shrubs, with large flower trusses, and a distinct scent of privet inherited from ancient genes. If you’re expecting the usual lilac perfume, the Preston plants will surprise you.

The French hybrid lilacs in my back garden have become quite leggy, and some have reached 15 feet (4.5 m) in height, with all the flowers coming at the top. This is very nice for my neighbour’s second-floor balcony, but it’s not as satisfying for me down below in the garden. It’s time to lower the height on these plants, and the pruning must be done immediately after flowering is finished to avoid sacrificing next year’s flower buds. There’s no time to waste!

The basic approach is simple, and focuses on rejuvenating the plants by removing up to one-third of the stems each year, for three years, and stimulating new stems that will eventually carry flowers. Lilacs bloom best on younger wood, so I’ll begin with the oldest stems that have grown more than two inches (5 cm) thick. I’ll also take out anything that’s broken, or weak and twiggy. Lilacs react quickly to pruning, sending up suckers from the base. That’s a good thing, as the strongest of these will be the ones to save and develop into a well-shaped shrub. I’ll save three or four of the best suckers, and eliminate the rest. I’m aiming for a plant about eight feet (2.5 m) tall, with flowers blooming at all levels. It may take a few years to bring these tall lilacs back to a more manageable size, and the strong new sprouts from underground will bloom in three to four years. Lilacs need shaping every year to ensure there is always vigorous new wood developing, while older stems are removed. That’s the way to disappoint the neighbours and keep lilacs blooming where I can see them.

Thanks for visiting at Making a Garden.