Are you looking for something just a bit different by way of ground cover? Maybe something taller than wooly thyme or mazus reptans, but with a similar pop of color? Cotoneaster horizontalis is an excellent choice!
Brilliant red berries decorate this deciduous shrub once it has stopped flowering. Small, rounded dark green leaves give an almost lacy look to its branches. And in the fall, the leaves turn brilliant shades of orange and red, just in time for your Halloween display.
It isn’t anywhere near as low-lying as most of the popular ground cover plants. This one isn’t a good choice for a lawn replacement, as an example. But if you’ve got a hillside that needs erosion control, or border space that needs something, this is absolutely perfect.
Let’s talk about rock cotoneaster and how to maintain and care for it!
Good Products For Cotoneaster Horizontalis:
- Monterey BT
- Garden Safe Neem Oil Extract
- Safer Brand Insect Killing Soap
- Safer Brand Horticultural & Dormant Spray Oil
- Dr. Earth Ready-To-Use Disease Control Fungicide
|Scientific Name:||Cotoneaster horizontalis|
|Common Name(s):||Rock cotoneaster, rockspray cotoneaster|
|Height & Spread:||2-3′ tall, up to 8′ spread|
|Sun:||Full to partial sun|
|Soil:||Well-draining, loamy, can tolerate poor soils|
|Water:||Average – keep soil moist but not wet|
|Pests & Diseases:||Cotoneaster webworm & lace bugs worst pests, fire blight possible|
All About Rock Cotoneaster
Cotoneaster is a deciduous, spreading shrub. It grows with stiff and evenly-branched sprays of foliage. These sprays develop a distinctive herringbone pattern which is quite appealing.
The tiny, rounded leaves are quite pretty. Glossy and green through most of the year, they turn vibrant shades of red and orange in fall. The plant loses all greenery for the winter. Denuded branches maintain their stiff fan-shape.
In the spring months, pink-tinged flowers appear. These are rarely clustered, instead appearing in ones or twos evenly across branches. As the flowers fade, the fruit begins to appear, and a myriad of small berries form. These begin as yellowish fruit, but will turn a brilliant scarlet color.
The plant has a natural layering effect which is beautiful. The stiff, semi-hardwood branches fan out overtop each other. This provides a visual effect of filling in the gaps between the branches. But it does make it a bit difficult to remove fallen leaves under the branches in the late fall.
Native to China, the tiny leaves and brilliant berries have made this a garden staple in many other areas. It’s especially popular in cooler climates, preferring USDA zones 5-7. Coastal climates and mild regions provide a perfect home.
It is larger than most ground cover plants, growing two to three feet tall and up to eight feet wide. As a border plant or hillside foliage, it does phenomenally well. It’s an effective erosion controller, too.
Caring For Your Cotoneaster
The tumbling display of this plant works well in cascading rock gardens, in long beds, and on hills. It can be grown as a container plant as well, although it prefers long planters to narrow pots. The foliage is somewhat rigid, and thus may not look ideal in all container types. It’s truly best as an in-ground planting option.
Light & Temperature
As I said above, zones 5-7 are ideal in the US. It’s especially popular now in coastal gardens due to their milder temperatures. This plant can struggle in hotter climates, and isn’t the best choice for zones 8 and above.
It tolerates full sun to partial shade, but doesn’t flower well in full shade conditions. I recommend providing a location which has morning sun and afternoon shade. This ensures that your plant has a little cooler conditions during the peak heat of the day.
Water & Humidity
Once established, rock cotoneaster can handle drought like a champ in partial shade. Full-sun plantings need a bit more moisture, as do younger plantings while they grow.
Consistent soil moisture is better than wildly-fluctuating conditions. If you can provide a small amount of water on a consistent basis, it’s better in the long-term for these plants. Consider soaker or drip irrigation underneath the foliage for ease of watering.
Humidity-wise, this plant is fine as long as there’s consistent airflow. They’re not generally susceptible to many of the moisture-related diseases. Coastal conditions often provide enough air moisture that watering frequency is greatly reduced.
Like most plants that do well in coastal climates, this one tolerates slightly higher salt content. It is somewhat resistant to sodium-based ice melt products and road deicers, too. Try to minimize the deicer’s spread to the soil as much as possible. Moist, salty sea spray is fine!
In a perfect world, your cotoneaster plants would have loamy, well-draining soil. It would hold just enough moisture to sustain the plant, but water wouldn’t pool around the roots.
Poor soil is tolerated by these plants, but only if it drains off excess moisture. As deciduous plants, they provide a lot of organic material when they drop leaves in the fall. Over time, they can actually improve their own soil a bit just by dropping leaves. But if possible, new plantings should be in soil which has a lot of decomposed plant matter to start with.
Different pH levels rarely have an effect on this plant. It will tolerate a wide range of conditions from lightly acidic to lightly alkaline. If you aim for a neutral range, it’s easiest to maintain.
Fertilizing is best done when the plant is beginning to develop new leaves in spring. It needs a slightly higher nitrogen content for its greenery and for spreading. A 10-8-8 slow release is fine for spurring new growth.
If your goal is to maintain size and promote flowering/fruiting, opt for balance instead. A 10-10-10 is just fine if your plant’s already at your preferred size.
I prefer slow-release granular fertilizers for this plant, but you can use liquid options as well. With slow-release fertilizers, apply once in early spring. Liquid formulations can be applied once per season, but diluted to lower levels to avoid over-fertilization.
Propagation is best done from softwood cuttings in the early summer.
Select a healthy stem with plenty of young leaves, preferably one that’s vigorous. Remove lower leaves, and dip in water and a powdered rooting hormone. Be sure to cover some young leaf buds with hormone, as the roots will develop from the lower buds.
Sometimes, a version of air layering can be used to encourage further spread. Use a ground staple to secure a low-hanging branch to the soil at its midpoint. Be sure that some leaf bud points are just under the soil’s surface. This technique does not always work, so cuttings are more effective for propagation.
One of the beauties of the cotoneaster plant is that it seldom, if ever, requires pruning. Most pruning should be to prevent overflowing boundaries. Removal of dead or diseased wood is also an option. But because of its nature, it looks best when left alone!
If a disease has affected your plant, remove at least 8-12″ past the blighted part of the stem to be sure you get it all. Sometimes, this may mean cutting back to the main trunk of the plant. Use sterilized, sharp pruning shears. Between cuts, set your shears in a mixture of 1 part bleach to 9 parts water for at least 10 seconds. This ensures that every cut is sterile and you aren’t spreading disease.
As a general rule, very little will be a problem for your cotoneasters. While there are some pests and diseases that will impact them, they’re limited in scope. We’ll go over those specific problems now, and how to handle them should they arise!
Most cotoneaster issues develop from pests or diseases. Unfortunately, there are a couple other problems which could arise with these plants. They tend to be limited in scope and easy to fix!
Over or under fertilizing can create chlorosis, or yellowed leaves. If your plant’s leaves begin to yellow and it’s spring or summer, consider when you last fertilized. If the answer is “never”, it’s a good idea to fertilize with a balanced fertilizer.
In early spring as it forms leaves, your plant will need a bit more nitrogen than the rest of the year. But don’t go too heavy on it! A slow-release formula applied in the early spring should be ample nutrition.
Watering too much or too little is the other big problem. Overwatering can create conditions which lead to fungal root rots. Underwatering, while less of a problem, can lead to leaf-drop or plant weakness. Maintaining consistent, but not heavy soil moisture is best for these plants.
So prevalent that it’s named after the plant it feeds on, the cotoneaster webworm is a caterpillar. It feeds on plant leaves and can cause major defoliation of branches. The worse the damage, the harder the plant finds it to properly make chlorophyll.
Treatment of this caterpillar should be done with a bacillus thurigiensis spray. This bacterial spray will eliminate most forms of caterpillar. Only spray where necessary to kill off this webworm.
Lace bugs are another form of pest common in the western US. Not to be confused with the beneficial lacewings, lace bug nymphs will suck moisture from the leaves. This leaves a stippled, dotted surface and damages the leaves themselves. They also leave sticky, black excrement on the leaf surfaces.
Thankfully, lace bugs are easy to treat. Insecticidal soaps and neem oil both work well to eliminate these pests. Adding lacewings to your garden provides a natural predator for the lace bug.
Spider mites may come to call, especially during drier times. Regularly spraying down the foliage of your cotoneaster plants will reduce their numbers. A neem-based spray can keep them at bay.
Armored scale insects may develop from the late winter into the early spring. These typically attach to the branches of your plant itself. Use a horticultural dormant oil or neem oil in the fall and winter to prevent them from attaching.
Some forms of aphid, particularly the apple aphid, may attack your plant. While they do limited damage, they can spread disease easily. Neem oil will also handle these pests.
Cotoneaster horizontalis is especially vulnerable to the Cotoneaster fire blight. Caused by Erwinia amylovora, this causes many problems. A sticky ooze can develop on the twigs and limbs. Blossom blight can cause the flowers to go necrotic. Fresh shoots can develop a crooked shape, like a shepherd’s crook.
This same blight can cause cankers on the stems. These appear as sunken areas on the stems or branches. There may be cracking around the canker’s surface, especially as it dries. Active cankers will have an amber or brown ooze in or around the canker.
Erwinia amylovora can be a little hard to combat. With sterile tools, and sterilizing between cuts, removing infected branches is essential. Certain horticultural copper fungicides may be used in rare occasions. However, none of these formulations are available on the mass market. Incorrect use can cause serious harm to your plant. It’s easier to remove the damaged portions or to get professional help.
Entomosporium leaf spot is another common rosaceae family problem. This fungal-based leaf spot disease causes reddish spotting on the leaves. Sometimes the spots may be surrounded with a purplish halo. In time, the underside of the spot will develop spores and the disease will spread.
With this leaf spot, copper fungicides are again risky. There are some products made with essential plant oils and malic acid which may help. Removal of diseased branches is better, but be sure to also remove any fallen leaves. The spores of the disease can linger on leaf debris.
Frequently Asked Questions
Q: Can cotoneaster be evergreen?
A: In very limited conditions, yes… but those are pretty rare. The upper part of zone 7 might be able to maintain year-round foliage in sheltered conditions. Those locations would need to be frost-free zones. This means that some California coastal areas might work. But you’d miss out on that glorious fall color!
Q: Are cotoneaster berries edible?
A: Not for humans, dogs, or cats. Cotoneaster species can be poisonous to humans and pets, both the foliage and the berries. The California Poison Control Center considers them to be level 4 toxic plants. Many species of birds love them, though, and they are apparently able to handle their slight toxicity well. Keep children and small animals away, and resist the temptation to sample the berries!
It’s not as low-growing as most ground covers. But if you’ve got a large area to fill, rock cotoneaster may be a good choice. It makes a beautiful hillside landscaping shrub or pathway border. Low-maintenance, it’s definitely worth growing for its seasonal color!
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