Lilacs are renowned for their longevity and hardiness. Numerous lilac shrubs reach ages of greater than 100. They frequently outlive the residence of the gardener who planted them due to their extended lifespan. As a result, if you’re driving along a country road and come across a few what appear to be random lilac bushes, it was probably a farm or house a century ago.
Try growing lilacs in your garden if you haven’t already. They not only return every year, but they also put on a display for the senses with vibrant blossoms and enticing scents. Lilacs have a lot to offer, and learning about their history demonstrates just how unique these plants are.
Fungal diseases
The Plant Disease Clinic has analyzed lilac samples this season and found the fungal disease Lilac Pseudocercospora leaf spot to be present. The same symptoms have been recorded (yellowing then browning leaves, dieback).
The PDC places a strong emphasis on sanitation because it appears that Pseudocercospora spores can survive on plant detritus for a number of years (leaves, stems, dead flowers, bark).
- Clean up fallen leaves to help reduce the likelihood of reinfection next season.
- Consistent watering and renewal cutting to reduce density will sustain the stressed plant.
Several of the plants in our landscapes, including lilacs, are afflicted by verticillium wilt. Verticillium dahliae and Verticillium albo-atrum are the two fungi that cause it. For a plant with this fungus infection, there is no cure.
- As a result of the fungi clogging the branch’s vascular system and preventing the transfer of water and nutrients, individual branches turn brown and die quickly.
- To increase plant longevity, increase watering and fertilization.
- The disease can spread across all sections of the afflicted plant, thus the best preventive is to buy resistant cultivars and practice proper hygiene.
Insects
The Lilac Borer, sometimes known as the Ash Borer, is a clearwing borer moth that creates tunnels in lilac stems.
- Frass, sap, and sawdust are warning signs (excrement).
- Some plants can withstand this harm.
- Others see branch dieback, and occasionally the entire plant dies.
- They won’t likely catch anyone’s attention.
Jeff Hahn, an extension entomologist, confirmed that no lilac borer samples have entered his lab this year.
Herbicide damage
Broadleaf weed treatments on lawns may volatilize, changing to a gas, and float onto unintended plants if sprayed during periods of extreme heat and humidity.
Herbicide damage signs like cupping and browning would appear in patterns:
- along a hedge’s one side but not the other,
- bushes positioned in or close to lawn areas, at the same level throughout their bases,
- and most critically, away from the area’s predominant winds.
Lilac hedges next to agricultural fields or other sizable herbicide-treated areas may experience damage in this manner.
Do lilac bushes need to be pruned?
An old, overgrown lilac was one of the few plants that endured my garden restoration. The fact that it obscured my neighbor’s garage and, more importantly, sported steel-blue double flowers, led me to rescue it. Although the blossoms on this shrub were both lovely and fragrant, it was difficult to appreciate them because there were so few of them. I decided to go with a rejuvenation pruning because I knew there was no reason to give up on this long-neglected plant because lilacs can handle severe pruning.
On stems that are no older than five or six years, the common French lilacs (Syringa vulgaris cvs.) yield the most and the largest flowers. The flowers get fewer, smaller, and farther away as the stems get older. A lilac, however, may reliably produce blossoms for decades with the right trimming. The method you choose will depend on how old your shrub is. Plants are maintained annually to keep them healthy. A more drastic trimming may be necessary for lilacs like mine that have seen better days.
Lilacs should be clipped annually to encourage healthy stem development and strong growth that improves flowering. Cutting sick, deformed, and unproductive stems to the ground constitutes annual pruning. I thin and cut back some stems as well to promote healthy, evenly spaced growth. To prevent them from growing too far away from the center of the plant, I also pruned a few of the new shoots that emerged from the roots. I left a few inches between each stem to prevent crowding. Since they produce the most, I maintain the pencil-thick shoots that extend all the way to the ends of the branches. Small, twitchy growth is unproductive and won’t blossom. This growth can indicate an excess of aged, unproductive stems or too much shadow. Remove stems as soon as possible after blossoming, or in late winter if you don’t mind losing a few blooms. Cut off stems and shoots at or just below the soil line.
Dwarf lilacs rarely need pruning
Both the “Palibin” Meyer lilac (Syringa meyeri “Palibin”) and the “Miss Kim” Manchurian lilac (Syringa pubescens ssp. patula “Miss Kim”) are twiggy-habiting, somewhat small lilacs. On these types, just deadheading is needed in terms of pruning. You can prune some of the older stems as the plants get older to make place for younger, more robust stems. In contrast to regular lilacs, these plants hardly ever spread out of control. They might never need to be entirely regenerated if you only undertake a tiny amount of trimming every few years.
After the blooms have faded, deadheading, another aspect of annual maintenance, should be carried out as soon as feasible. Just above the two new shoots that slant out from the stem that stopped with the old bloom, the base of the old flower cluster should be cut off. The new shoots will develop throughout the course of the summer, produce flower buds, and culminate in a cluster of flowers the following spring. While not as crucial as the annual thinning, eliminating the old blossoms enables the plant to focus more of its energy on developing robust branches and flower buds. In June, I deadhead and thin my plants as needed.
While performing this yearly maintenance, I occasionally come upon a young, robust shoot that may be getting too tall but is still a good, productive stem and is a candidate for tipping off. I cut the wasted flower’s entire top stem back to one or two side shoots at the desired height rather of just cutting it off at the base. The side shoots that are now near the top of the bush are encouraged to grow vigorously and develop flower buds for the following year by this cut, which also aids in shrinking the shrub.
My own old, overgrown lilacs need more severe pruning. I went outside in the early spring before growth got going to get a good look at the bush. I looked to see if the plant had been grafted before I began chopping. I immediately cut it down to the ground as it hadn’t (for a grafted plant, see the panel below). I recognized that this drastic trimming would result in the plant losing part of its aesthetic appeal for a few years because lilacs bloom on the growth from the previous season. However, I was also aware that the reward—more blossoms and a stronger plant—would be worthwhile.
It’s crucial to nourish the plant after rejuvenation pruning with compost, composted manure, or a balanced chemical fertilizer and to make sure the soil pH is close to neutral, which lilacs appreciate. In the upcoming years, these supplements and some high-quality mulch will help to encourage vigorous new growth and enhanced flowering.
Has your lilac been grafted?
If your lilac has been grafted, check it out before you start making cuts to the stems. Grafting is a method of plant multiplication in which the scion, or branch, of one species is joined to the rootstock, or stem, of another species. This is typically done to enhance a plant’s look or traits. A graft union, where the cultivar’s scion wood joins the rootstock several inches above ground level, should be obvious. An apparent change in the bark from the rootstock to the scion’s bark, as well as a little swelling at the graft union, are things to watch for. If your plant has been grafted, all of your cuttings must be made above the graft union, and you must prevent shoots from the rootstock from developing into new flowering stems. Flowers of the desired shape or color will not be produced by shoots that emerge from the rootstock.
What can you do to revive a lilac bush?
You might believe your lilac is dying if you see it becoming a little frail or worn out, or if it only produces a few little flowers in the spring. Often, all a plant needs to produce robust new growth and abundant, fragrant blossoms is some hard pruning and some feeding. Rejuvenate a lilac bush by working with it just after bloom, when the blooms have dried up and are spent.
To get to the grass or soil layer, rake away any debris, dead branches, or fallen leaves from the lilac’s base.
Pick three to five of the lilac’s strongest branches after surveying the entire plant. Follow the branches you’ve chosen to the plant’s base, where you can flag each sturdy branch by gently tying a rope or ribbon around its base.
Use hand pruners or a handsaw if needed to make a clean, horizontal cut across all of the unflagged branches that are about an inch off the ground. To prevent breaking off any limbs you want to maintain, carefully pull the trimmed branches away from the lilac.
- You might believe your lilac is dying if you see it becoming a little frail or worn out, or if it only produces a few little flowers in the spring.
From the remaining branches, take off your sting or ribbons. Fertilize the lilac around its base according to the dosage and application guidelines provided by the manufacturer.
Mulch should be applied in a ring around the lilac’s base that is no deeper than 3 inches and no wider than 3 feet. New sprouts won’t be able to emerge if the mulch is too deep.
If there is a drought or excessive heat in your area during the summer, make sure the plant is well-watered. Lilacs require good drainage, but they don’t fare well in dry soil.
The next spring, watch for buds to start swelling on the branches. Reapply fertilizer right before flowering and once more after flowering is finished. This is how you should fertilize each year.
- From the remaining branches, take off your sting or ribbons.
- The next spring, watch for buds to start swelling on the branches. Reapply fertilizer right before flowering and once more after flowering is finished.
Maintain your lilac by doing minimal annual pruning to remove wasted flowers and only every three to five years to remove old and dead branches.
Avoid letting the feed come into contact with the branches when applying fertilizer to the area around the plant, whether it be granular or water-soluble.
Lilac bushes — do they age?
The common purple lilac is a hardy, dependable shrub that can grow up to 20 feet tall. Unfortunately, the lower, shady sections of lilac shrubs typically lose their leaves as they get older. Large, overgrown specimens as a result are frequently leggy and ugly. Pruning can restore or rejuvenate old, neglected lilacs. Home gardeners have two alternative pruning techniques to pick from.
Cutting the entire plant back to within 6 to 8 inches of the ground in late winter is one method of renewing a huge, overgrown lilac (March or early April). A significant number of shoots will sprout during the growth season as a result of this aggressive pruning. Select a few sturdy, robust shoots to construct the shrub’s framework, keeping a few of them, and cut off all the others at ground level in the late winter of the next year. To promote branching, head (clip) back the retained shoots to just above a bud.
Cutting back the overgrown shrubs over a three-year period is a second method for pruning mature lilacs. In late January, start the process by digging up and removing one-third of the big, old stems. The following year, trim out half of the remaining old stems (again in late winter). Additionally, trim out some of the recent growth. Keep a few healthy stems that are evenly spaced apart and cut off the rest. In the third year’s late winter, completely remove all of the old wood. It is also necessary to thin the fresh shoots more. This pruning technique should enable you to take pleasure in blossoms every spring because lilac wood must be three years or older before it blooms.
Within a few years, with the right pruning, an old, overgrown lilac can be converted into a robust, appealing shrub. Pruning should be a frequent component of the lilacs’ management regimen after they have been revived. By cutting a few of the oldest branches every three to five years, the shrub can be kept strong and healthy.
(This article, which first published in the Sunday edition of the Lincoln Journal Star Newspaper in February 2005, has since been amended. Consult the Terms of Use for details on how to copy this content and use any images or visuals.)
What destroys lilac bushes?
A common chemical component of broad-spectrum herbicides is glyphosate. This poison will enter the living cells and start killing the roots when applied to the open wounds on the lilac stumps. One hour after trimming the exposed growth is the ideal window of opportunity to apply glyphosate. Check the area for the appearance of tiny, thin suckers that also need to be treated while spraying the glyphosate to the stumps that were clipped. At least 24 hours are required for the glyphosate to start acting. Rain or watering before this period will wash the chemical away and reduce its potency.
Are lilac bushes suited to coffee grounds?
Lilac plants don’t require a lot of food or fertilizer. A 10-10-10 fertilizer mixture applied yearly in the early spring is what we advise. (The amounts of nitrogen, phosphorus, and potassium, or NPK as they are popularly known, are represented by the digits 10-10-10 in the formula.) Early spring fertilization of lilacs with a high phosphorus solution encourages blossoming.
Coffee grounds and grass clippings are also excellent sources of nitrogen. Use in moderation since an excess of nitrogen in the soil can lead to subpar blooms. The ideal soil conditions for lilacs are slightly alkaline (6.5–7.0 pH), wet, and well-drained. The soil may become more alkaline by adding bone meal to it. Use Miracle-Gro Shake ‘n Feed Flowering Trees & Shrubs Plant Food in the spring if you decide to feed your plant. Last but not least, lilac plants dislike acidic soil. Epsom salts can be used to encourage blossoming while the plant is dormant.