Forsythia Leaves Turning Yellow – Reasons For Yellow Leaves On Forsythia
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By: Bonnie L. Grant, Certified Urban Agriculturist
Forsythias are hardy, attractive bushes which delight us every spring with their early, golden blooms. The plants are relatively unbothered by insects and can withstand cold, heat and short periods of drought, but fungal diseases are a serious threat to their beauty. If you see your forsythia leaves turning yellow, it could be a sign of a significant fungal issue. Yellowing forsythia bushes are normal before fall leaf drop but during the growing season it’s time for action.
Why are Forsythia Leaves Turning Yellow?
Periods of rain during the warmer seasons create a humid, moist atmosphere which is perfect for the formation of fungus. Fungal spores can often live in soil for a long time and even overwinter there, bursting into infectious displays at the first sign of favorable weather. There are several fungal diseases that may be plaguing yellowing forsythia bushes. A fungicide can be helpful but it is best to try to identify the disease for more effective treatment.
If you can rule out overcrowding, dry conditions and topical injury as well as any pests, you are left with a plant that probably has a fungal disease. Yellow leaves on forsythia occur from a variety of diseases, most of which can trace the vector to grafting or mechanical introduction, although disturbed soils may harbor spores for years.
Maintaining a healthy plant through regular watering, fertilization, pruning and mulching can help minimize the damage from fungal disease. Forsythia leaf problems will not usually kill the plant, but due to its ornamental function, the disease can mar the beauty and dim the plant’s vigor.
Diagnosing Yellow Leaves on Forsythia
A forsythia with yellow leaves may be occurring due to any number of diseases. Below are the more common ones:
- Yellow veins may indicate tobacco ringspot virus or arabis mosaic virus. Each is generally introduced through nematodes.
- Yellow, black or brown spots that form a larger necrotic tissue can mean that forsythia with yellow leaves are caused by anthracnose, one of the most common fungal diseases on ornamental plants. The yellow tissue may also be colonized by tiny fruiting bodies.
- Sclerotinia sclerotiorum begins with yellow leaves but advances to wilted stems and damage deepening to brown.
Treating Forsythia Leaf Problems
Fungicides are generally only effective if sprayed before the plant shows signs of disease. This is usually just at leaf formation. Once you notice a forsythia with yellow leaves, it is too late to make use of a fungicide.
Treatment would include pruning to open the canopy and allow airflow through the plant and cleaning up any dead plant material around it. Minimize the splash of soil bound spores by watering gently at the base of the plant. Use a solution of 70 percent alcohol to clean any tools used to prune or rake around the plant.
Maintain the plant’s vigor with regular watering, feeding and sterile pruning. The next year, in early spring, use a fungicide spray to prevent future occurrences.
Forsythia leaf problems don’t announce the death knell of the plant but they are inconvenient and unsightly. Early prevention is key to preventing further issues.
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Read more about Forsythia
What Kind of Pest Attacks Forsythia Bushes?
Forsythia are deciduous shrubs with vibrantly-colored blooms. Commonly used for borders, screens and espaliers, the plant is covered with bright yellow four-petaled flowers lining branches in spring, followed by green foliage. Depending on the species or cultivar, they grow up to 10 feet tall in U.S. Department of Agriculture plant hardiness zones 8 and 9. Forsythia resists most pests and diseases, but a few pests can cause problems for the shrub.
What to do if your forsythia bush won't bloom
Q: I have a forsythia bush and for the last couple of years it hasn't bloomed. Sometimes it only gets a couple flowers when it does bloom. Do you know the reason for this and what I could do?
—Darlene Green, Lehighton
A: Forsythia bushes usually are quite easy to grow. The most common problems are planting them in too small a space or deciding that they should make a tidy, square hedge. Both situations require a lot of pruning and fighting the nature of the plant, which are graceful, arching branches on an 8-to 10-feet-tall and wide bush.
But let's move on to Darlene's problem. Forsythia don't bloom for a few reasons:
•Not enough sun: Forsythias like sun, and if the surrounding plants grow over, increasing shade, you will have decreasing blooms — sometimes no blooms. Trim back the shading foliage on nearby plants to increase the available sunlight or move the forsythia.
•Older plants don't bloom: Forsythia bushes grow to a finite size. If you don't prune them, you will experience fewer and fewer blooms as the plants bloom on the previous year's growth and your plant growth slows.
Cut back the plant to rejuvenate older growth. Some find the drastic cut to the ground method too drastic but the forsythias usually do grow back full of young, lush growth and flowers. Others prefer a more moderate technique where a third to a half of the canes are cut back to the ground. This gives the plant a complete revitalizing over a two to three year period.
Improper pruning: First and foremost, forsythia bushes are not meant to be square and if you choose to prune yours that way you are in for a lot of work. Second, pruning off just the outer ends of the branches—running the hedge trimmer over them, will create a dead, bare center and probable naked branches on the bottom of the bush. But, third, often the problem is simply pruning at the wrong time. Forsythia bushes form their buds on new growth very soon after blooming.
If you want to avoid cutting off next year's flowers, prune forsythias in the weeks immediately after they bloom.
Q: I bought an orchid last year. I bought quite a few over the years, but had no luck with them coming back again. This orchid survived and it has quite a few buds on it, but as I know nothing about orchids I am wondering what are those growths coming out of the bottom of the stems. There are so many of them, they are overwhelming the plant. Do I cut some of them off or just leave them alone? There are about 15 of them and some of those are splitting off.
A: Since you are alarmed by the growths, I am guessing that you are not talking about new green leafy growth. The snaky, smooth growths often seen at the base of orchids are aerial roots, similar to regular roots but with a covering designed to absorb moisture but not lose it.
It can be a sign that your orchid needs repotting, something that should be done about every two years since the bark mulch used in most orchid planting medium breaks down and needs replacing. However, the time to repot is not when the plant is actively growing or before blooming. Allow the plant to bloom and then consider repotting.
Note that you should consult a good orchid reference for specific instructions on pots, medium and the burying or removal of roots. American Orchid Society (www.aos.org) is one source. Consider attending the local Lehigh Valley Orchid Club (www.lvos.org) meeting. The club usually meets on the first Sunday of every month at Channel 39, WLVT studio on the SteelStacks campus in south Bethlehem.
Q: In a recent column you mentioned the use of a flame weeder to eliminate weeds in stone covered areas. I have many stones surrounding my shrubs, and the weed problem is constant. Would you kindly expound on this product and where it can be purchased?
A: The flame weeder is one of my favorite garden tools. It consists of a burner think of those old burners in the chemistry lab, and a hose or tube attached to a propane tank. The weeder works best by heating the water in the weed and bursting the cell walls, killing the plant by igniting it and burning it to a crisp. Besides the enjoyment from destroying the weeds, flame-weeding avoids the use of herbicides.
There are small models with camp-stove size propane tanks and larger ones that connect to the gas grill sized tank. They are available online and the smaller versions are often available in garden centers. Red Dragon is a popular brand Bernzomatic is another.
Care must be taken to assemble it properly, securely connect hoses or pipes and to follow all directions — many have self-ignition systems but others may require a lighter to ignite. Use flame-weeders in areas that are bricked or paved, concrete areas or those covered with stone or gravel. Because of the fire hazard, flame weeders are not recommended for area with mulches such as dried grass, leaves, shredded bark, wood chips or rubber mulch.
Busy Workers' Plant and Attic Treasures Sale: 8 a.m. to 4 p.m. May 11 at the Central Moravian Church, Christian Education Building, 40 W. Church St., Bethlehem. 610-866-5661. Flowers, vegetables, herbs, annuals, perennials, hanging baskets and daylilies. Attic treasures and crafts, baked goods, food and Moravian sugar cake. Sales benefit charities from Bethlehem to Tanzania and Nepal.
Sue Kittek is a freelance garden columnist, writer, and lecturer. Send questions to Garden Keeper at [email protected] or mail: Garden Keeper, The Morning Call, P.O. Box 1260, Allentown, PA 18105.
•Start seeds for: Eggplant, summer squash, and winter squash, baby's breath, cosmos, and zinnias.
•Direct sow: Cabbage, carrots, collards, bunching onions, onion sets, parsnips and Swiss chard, Chinese cabbage, endive, escarole, kale, kohlrabi, leeks, head lettuce and leaf lettuce, beets, broccoli, Brussels sprouts, cauliflower, peas, radishes, spinach and turnips.
•Plant bare-root trees and shrubs when soil is dry enough to work. Plant perennials and cool-season annuals.
•Visit nurseries as they open for inspiration and new plants.
•Prune and divide perennials. Hostas and daylilies are up and ready to divide.
•Cut back ornamental grasses. Divide clumps when you see new growth.
•Test soil for new beds. Retest soil in poorly performing areas or if you haven't tested in the last 3-5 years.
•Apply broadleaf weed control in the lawn by the end of May. If you use corn gluten based weed control in garden beds, begin applying now and repeat as directed, usually at 4- to 6-week intervals.
•Dethatch lawns by mid May. Apply spring lawn fertilizer treatments by mid June.
•Complete sod projects by the end of May to allow the grass to establish before the heat of summer. Seed lawns now until mid-May.
•Consider applying a top dressing of compost to lawns and beds. Fill in holes or dents in lawns before seeding or sodding.
•Apply or fluff spring mulch. It should be 2 to 3 inches deep and applied a few inches away from foundations, tree trunks and other plants.
•Dump standing water and remove anything where rainwater can collect in stagnant pools, where mosquitoes can breed.
•Clean gutters and downspouting.
•Check hoses replace washers and correct leaky connections before connecting to water source.
•Check summer bulbs and pot up for early bloom.
•As the weather warms, begin to ease out the hardiest of your wintering over plants.
•Feed birds regularly and provide fresh water. Gather and set out nesting supplies, clear out and clean birdhouses.
•Tools, equipment, and supplies
•Replenish, organize and inventory potting supplies. Clean display containers, window boxes and other planting containers.
•Replace worn or broken tools. Clean, sharpen and oil hand tools.
•Prepare winter equipment for storage.
•Prepare spring equipment for use. Sharpen blades, get fresh gas, check and/or replace oil. Send mowers and tractors for tune-up or repair.
•Check for ticks after every outing.
•Wear gloves to protect hands. Use eye protection and ear protection when using loud power tools.
•Rake lawns and remove sticks before first mowing
Greenstem Forsythia is a deciduous shrub in the Oleaceae family that is native to Asia. It is widely used for its early yellow flowers which provide needed relief from winter. It will grow to 10 feet tall and wide with arching stems. The plant takes well to pruning after flowering and can be cut to the ground for rejuvenation.
Plant in average garden soil in full sun for best blooming. It is tolerant of a variety of soils. Use in a shrub border, as an accent or foundation plantings.Form in bloom Enrico Blasutto CC BY-SA 3.0 Form Fanghong CC BY 3.0 Flowers Tanakawho CC BY-NC 2.0 Plant houroumono CC BY 2.0 Mass planted Tanaka Juuyoh CC BY 2.0 Flower and leaf detail Tanaka Juuyoh CC BY 2.0 Stem and buds Rolf Engstrand CC BY-SA 3.0
Forsythia: A Spring Garden Stalwart Shrub
Gold Standard, With its boughs laden with brilliant yellow blooms, forsythia earns its
place as a spring garden stalwart.
Subtle is not an epithet anyone ever applied to forsythia, the well-known shrub that turns the color of a Colman’s Mustard tin each April.
For many gardeners, it is a step too far. But no one can deny its cheerfulness, and if you enjoy cutting garden flowers, its branches bring a ray of spring sunshine into your home, often at Easter.
Forsythia belongs to the olive family, Oleaceae, its species mainly found in east Asia. Botanist Carl Peter Thunberg spotted Forsythia suspensa in a Japanese garden in the late 18th century.
By 1833 F. suspensa had made its way to Holland, and by the middle of the century, Veitch Nurseries were selling it in England.
At around the same time, Scottish plant hunter Robert Fortune discovered F. viridissima in
He sent it back to the Horticultural Society (the society only became ‘Royal’ in 1861), in whose garden it flowered in 1847.
Nursery workers crossed the two species, and it was this breeding that gave us Forsythia x intermedia and its hybrids, which make up most of the forsythia on offer today.
The shrub was named after William Forsyth, an Aberdeenshire man who trained at the Chelsea Physic Garden and was superintendent of the royal gardens at Kensington and St James’s Palace 1784 until he died in 1804.
He was one of the Royal Horticultural Society’s founder members and great-grandfather of landscape gardener Joseph Forsyth Johnson, great grandfather to the entertainer Bruce Forsyth.
Forsythia always looks best left to grow naturally, without pruning. In Trees and Shrubs Hardy in the British Isles, the oracle W.J. Bean suggests sitting them:
“where they can grow freely yet are not so remote from the comings and goings of daily life that the birds can destroy their flower-buds undisturbed.” Other than avian interference, expect few problems.
The shrub featured in the 2011 film Contagion by Steven Soderbergh, which was prescient of the Covid-19 pandemic.
Jude Law played a conspiracy theorist who claimed a forsythia-based remedy could cure the film’s deadly virus.
Does Steven Soderbergh have a penchant for yellow spring shrubs, perhaps?
How To Grow Forsythia
Forsythia is an easy shrub to grow in sun or light shade, doing best on rich soil since
it’s a hungry plant.
After the flowers have faded, its mid-green leaves look rather plain, so plan to grow
something else nearby to supply interest from early summer onwards.
If left unattended, forsythia shrub may transit to a rather strange-looking shape one of the features is that branches spring out in arbitrary directions.
Many of us prefer this crazy look, and you should not think of annual pruning to be mandatory by all means.
If you like your bush’s shape, you can leave it for a couple of years without pruning.
On the other hand, if you are more into a decent shape, you can go ahead and prune your bush as per your liking to shape it into a more sightly shape.
Forsythia bushes pruning is best done after they have completed blooming in the spring hence the next spring’s flowers will blossom on wood formed the previous year.
Therefore, if you prune after the end of July, you may face the risk of losing all of the flowers for the following spring.
This will not ruin the plant. However, it means you will have shabby shrubs for a year.
Start by pruning approximately a quarter to a third of the original branches, cutting them to the ground.
That will boost new growth and a more solid form. After this “renewal” pruning, you may as well selectively cut fresh branches to expand upon the overall shape of your forsythia.
Common Pests and Diseases
Forsythia plants can be susceptible to knobby galls appearing along with the stalks, also fungal twig blights.
The two problems are best resolved by removing affected stalks. Twig blights can be averted by maintaining the plant correctly pruned to increase air circulation, and of course, by using a fungicide.
Untimely frost may kill the flower buds in climate zones borderline with the plant’s hardiness rating.
A variety rated for zone 5, for example, may occasionally lose its flowers in an area 5 garden if an early cold spell hits.
This will seldom kill the plant, and the flowers generally return after a year of no blooms.
5 Reasons to Prune Hard
Hard pruning may be warranted in the event of a variety of adverse conditions.
Let’s take a look at the top five.
1. Winter Kill
A cold-damaged forsythia that doesn’t bounce back in springtime with flowers and foliage may have suffered “winter kill.” This is a catchall phrase for plant tissue death directly related to extreme cold, freezing, and/or wind.
If a shrub shows no signs of life above ground, there’s always a chance that the roots below are still alive. They stay pretty warm in winter, especially beneath a layer of mulch and/or snow.
Before presuming it dead, trim all canes as close to the crown as possible. If no growth is evident by fall, dig up and remove it.
2. Widespread Disease
Although this is a sturdy shrub, it is not immune to disease, especially when stressors like cold damage, old age, and over- or underwatering make it vulnerable.
Weak plants, especially overly dry ones, often attract pests that can carry diseases.
Common forsythia diseases include gall, leaf spot, and twig blight. And while minimal damage may only require the removal of affected stems and the application of a fungicide, severe infestation or infection, especially in an old or unhealthy shrub, may call for a complete rejuvenation.
3. Extensive Physical Damage
During the growing season, forsythia stems are supple and sturdy because they contain moisture, and are able to bend without breaking.
However, late in a cold, dry winter, they are not as flexible, and can snap in a gusty wind or ice storm.
During the repeated freezing and thawing cycles of winter, a shrub may rise up out of the ground, a phenomenon called “heaving.”
When the ground thaws, settle it back down and assess the damage at spring flowering time.
If there are multiple broken canes, dead stem tips, few to no flowers, and little to no foliage, cut all of the canes close to the crown and start over.
In the event of major damage from a fallen limb, mowing equipment, or other stressor, a full cut-down may be in order.
Forsythia is wonderful in the spring. It’s one of the first bright spots in the landscape. However, it’s easy to forget it for the rest of the growing season, when it becomes a lush green backdrop to summer floral displays.
Forsythia is a long-lived shrub that grows fast. Some cultivars reach 10 feet tall. But there can be a difference between a long life and a good life.
All forsythia varieties benefit from a yearly trimming of up to one-third of their old canes to promote vigor.
Shrubs that reach old age without having been refreshed yearly may be big, but not robust. The aging process varies, and can be adversely affected by factors like prolonged moisture stress and extreme cold.
If there are loads of canes, but few flowers and sparse foliage, it’s likely because growth has slowed, so there is less new wood each year to form buds.
Cut all stems down to the crown, then put this bush on a yearly pruning regimen. Just after spring blooming, remove up to one-third of last year’s growth to the base of the canes.
Also, if a younger bush has taken over the garden, cut it down and put it on the same regimen. In two to three years, after it’s reestablished, relocate it as desired.
5. Excessive Top Pruning
If only the tops of hedges or stand-alone specimens are blooming and growing foliage, it may be time for a complete transformation.
This can happen over time when our regular pruning habit is to take a little off the top each year to maintain a particular height and/or shape.
In our tips for pruning, we suggest removing canes to their points of origin. The new canes that grow are long and contain many flower and leaf buds that come out the following spring.
Trimming the tops off bushes results in dense, twiggy growth, and bottom canes that are old and bare.
Take bare-legged shrubs down to their crowns with cutting tools, and let fresh, new ones grow up.
As mentioned, cutting the first flush of foliage by one-half promotes lateral branching near the base. This adds stability that is especially beneficial in windy regions with lots of freezing and thawing in wintertime.
Living the Green Life
Forsythia is generally a healthy shrub that’s not fussy about soil, tolerates drought, and grows like a weed.
But when moisture stress, pests and disease, nutritional deficiency, mechanical damage, and toxic exposure start a downward spiral, we need to act quickly to restore the growing environment, and ensure armloads of beautiful spring blooms followed by lush greenery all season long.
Do you grow forsythia? Have the leaves turned yellow? Share your experience with us in the comments section below.
If you found this article informative and want to learn more about forsythia care, we recommend these guides for further reading:
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About Nan Schiller
Nan Schiller is a writer with deep roots in the soil of southeastern Pennsylvania. Her background includes landscape and floral design, a BS in business from Villanova University, and a Certificate of Merit in floral design from Longwood Gardens. An advocate of organic gardening with native plants, she’s always got dirt under her nails and freckles on her nose. With wit and hopefully some wisdom, she shares what she’s learned and is always ready to dig into a new project!