Tag: lilacs

When to prune spring-flowering shrubs
‘Agincourt Beauty’ lilac (Garden Making photo)
I had a walk around the block this weekend, and it seems like all the spring-flowering shrubs are in bloom at the same time. The alternating weeks of warm and cool temperatures in southern Ontario have confused the orderly progression of bloom, and they’ve expressed their frustration by just getting on with it. I saw Japanese quince, Japanese kerria, magnolia, honeysuckle vines and shrubs, beauty bush, rhododendron, bridalwreath spirea, Korean spice viburnum, the May-blooming ‘Canary Bird’ rose and, of course, lilacs all in flower. Although the plants seem to have taken bloom times into their own hands, there’s far less leeway when it comes to pruning them.
Woody plants that bloom in spring have a resting period of about three to six weeks before they begin preparing flower buds for next year’s bloom. If the plants require hard pruning for size control or just gentle shaping, pruning must be accomplished during the rest phase to avoid cutting off nascent flower buds. It’s easy to forget this as they pass out of bloom and the first wave of early summer perennials begins a distracting display, but if I let the window of opportunity slip by, and start pruning in midsummer, I’ll forfeit next year’s show. However, if I make the necessary cuts and adjustments during the next few weeks, they’ll set their flower buds on the available wood, and I’ll have a better-shaped plant, full of bloom, next spring.
Some shrubs don’t require pruning, while others need a bit of shaping or perhaps removal of dead twigs and branches. The plants that always confound me are lilacs. They want to be 12 to 15 feet (3.5 to 4.5 m) tall, and it’s a mistake to fight the genetic programming that spurs them on to those heights. But a couple of mine are now headed for 20 feet (6 m), and that’s the approximate height of a two-storey house. All the bloom is carried at the top where sunlight is available, above sparse foliage. Attempting to resolve this pruning dilemma is going to require gritting of teeth and patient resolve.
Lilacs respond well to hard pruning, although not in exactly the way we would like. They renew themselves through suckering, sending up a small forest of thin new wood from the roots surrounding central trunks. It’s not unusual for one massive cut to stimulate two or three dozen suckers. It’s all good, viable wood, but perhaps too much. A selection must be made, and most of the suckers will need to be pruned out. The selected new suckers can be allowed to grow on, and eventually will begin blooming in about three years. It might seem a long wait for flowering, but that’s the way lilacs respond and there’s no hurrying them.
There are two scenarios in lilac pruning, and both stimulate new suckers. An old, neglected lilac with multiple trunks and many suckers can be rejuvenated by selectively thinning some wood (both thick central wood and suckers), and cutting them down to the ground. As new suckers rise in response to the pruning, determine which will remain and eliminate the others. The second method is best for tall, gangly lilac trunks with no suckers present. This is a gradual pruning, cutting one large trunk to the ground each year until the plant is entirely replaced by sucker growth. Once the large trunks are removed, the renovated lilac will be entirely replaced by suckers and a few of these must be removed each year.
Although I’ll miss a few years of flowering from these two lilacs, I enjoy pruning. It’s a quiet pleasure, and will eventually result in lilac flowers at nose level.
More from Judith Adam
When to apply spirng fertilizers
New dwarf butterfly bushes
When to prune Japanese tree peonies
May 28, 2013
Tree peonies and their kin
Mauve tree peony (Photo by Brendan Zwelling)
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
‘Agincourt Beauty’ lilac (Garden Making photo)
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.

June 7, 2011
Coping with clay soil
Lilacs perform well in clay soil (Garden Making photo)
Simple clay amending techniques for a clod-free garden
After almost 40 years of gardening, I’ve learned that the limitations of climate, shade and space are nothing compared to coping with heavy clay. Wise plant choices help mitigate the shortcomings of shade and a small lot. Careful cultural practices lessen the impact of drought and unwelcome frosts. But coping with sticky, dense, unrelenting, unforgiving, heavy clay has broken more than a few shovels — and has nearly broken my spirit as I’ve watched plants struggle in its grip. If only I had known then what I know now, I would have spent much more time improving my soil and less time buying plants at the nursery.
A short lesson in soil
Soil is a combination of minerals, organic matter, water, air and micro-organisms. The mineral component is made up of various-sized particles; clay is the smallest, sand is the largest, and silt falls somewhere in between. The proportion of each component determines the texture and structure of your soil.
The best soil is loam — a balanced mix of clay, sand and silt. I don’t believe it actually exists, and suspect it’s one of those unreachable goals presented to frustrated gardeners, like slug-free hostas and weed-free rock gardens.
Soil composed mainly of clay is heavy and dense because its small particles fit closely together. That’s why it’s so difficult to dig (see Characteristics of Clay, to find out if you have this type of soil). As well, water drains slowly because of clay’s compacted nature, and there is less oxygen available to plant roots. Although clay soil is often waterlogged in spring, during periods of drought it hardens, and water often rolls off the concrete-like surface before it has a chance to penetrate down to thirsty roots. As bleak as all of this sounds, there is one benefit to clay soil: it usually holds more nutrients than sandy soil; the latter has bigger spaces between particles, which causes water and nutrients to leach away quickly.
While working with clay is tough on gardeners, the biggest issue for plants is the slow drainage. Improving its structure (see Clod Busting,) improves drainage; planting in raised beds made with good soil also helps. With careful management and generous additions of organic material, clay soil will improve over time — lots of time. And remember that it’s an ongoing process. The soil will become more workable, but expect to spend a few years amending clay before you notice an appreciable difference.
Characteristics of clay
You know you have clay soil if:
- the soil is sticky and difficult to dig
- digging often results in huge clods that are hard to break up
- the soil is heavy and slow to  warm up in spring
- during a stretch of dry weather,  the surface hardens and cracks
- the soil is slow to drain
Digging in clay soil produces large clods that are difficult to break up (Photo by Joanne Young)
Clod busting
1. Clay soil is easily compacted. Avoid walking on cultivated soil, especially when it’s wet, or compressing it with heavy equipment. Digging wet clay also compromises its structure and will set back your efforts to improve it.
2. Amend clay soil by adding plenty of organic material, such as well-aged compost, sawdust (but not from pressure-treated wood), composted manure or leaf mould (partially decomposed shredded leaves). Coarse materials are better than fine ones. Do this repeatedly and as often as possible. For example, when making a new bed, spread several inches of organic material over the area and dig it in at least eight inches (20 cm) deep. When moving or adding new perennials to an existing bed, throw a shovelful of compost into the planting hole.
Organic materials prompt mineral particles such as clay to come together in clumps, called  aggregates. The various sizes and shapes of these clumps help form larger pore spaces, which creates more room for oxygen and water to move around plant roots. Organic materials also attract earthworms and micro-organisms that will munch and digest their way around the soil, loosening up  its structure even further.
3. Hand digging clay is preferable to using a tiller, which pulverizes soil into too fine a texture. Digging with a shovel leaves clumps of various sizes that allow a better exchange of oxygen in the plants’ root zone. Dig down at least eight inches (20 cm) when amending. Fall is the best time because soil is usually drier than in spring. Leave rough clods to allow snow to further break down the soil.
4. A two- to three-inch (5- to 8-cm) layer of organic mulch, such as shredded bark or leaf mould, helps keep the soil from forming a crust. It also ups the quotient of organic matter.
5. Adding sand can make matters worse; to have a positive effect, it must be coarse builder’s sand (various-sized particles; not horticultural or play type sand) and copious amounts are needed—at least one part coarse sand, one part organic matter and one part existing soil. Adding too little or too fine a sand creates the perfect conditions for making bricks!
Planting trees & shrubs in clay
- Dig a hole at least twice the diameter of the root ball, but no deeper than its height. Rough up the sides to make it easier for roots to penetrate. Don’t add gravel to the bottom in hopes of improving drainage. According to research done at the University of Minnesota, a layer of gravel creates a perched water table that causes the soil above the gravel to hold even more water.
- Position the root ball in the hole, ensuring that it sits at or slightly above grade; plants that settle below grade can suffer from root rot.
- Backfill with the soil you removed (if it’s relatively fertile) or amend it slightly by adding organic matter. If you amend the backfill material too radically, the resulting drastic change in soil fertility and texture will discourage roots from spreading out beyond the sides of the hole. It’s best to heavily amend the whole bed or border than individual planting areas wherever possible, but it’s better to amend a single planting hole than do nothing at all.
More about soil
An easy way to make soil
July 9, 2006

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