Your lovely evergreen ceanothus has been growing beautifully throughout spring, when suddenly you notice several of its leaves turning yellow. Naturally, this will have you worried!
Ceanothus leaves can turn yellow due to improper watering, prolonged sunlight exposure, overfertilization, or natural aging. Before you panic, take a few deep breaths and assess your plant’s condition. Sometimes, all you need to do is tweak your plant care routine to save the entire plant from yellowing.
Ceanothus plant care basics
One of the many reasons gardeners love ceanothus is due to its impressive display of beautiful blue flowers. Also known as Californian lilac, blueblossom, or buckbrush, ceanothus is endemic to the Pacific coast of North America. It belongs to the Rhamnaceae family and includes more than 60 different species that are identified as small trees or shrubs.
While most ceanothus species produce blooms in shades of powder blue to azure, a few cultivars can also have pink or white flowers. Depending on the variety, these sweet, fragrant blooms mostly emerge during the spring and summer, with certain cultivars blooming in the fall. This means you can choose ceanothus cultivars to fill your garden with flowers across most of the year!
If you plan to grow these dazzling blooms in your area, keep in mind that most ceanothus species thrive in zones seven to nine. A few cultivars, like the Ceanothus americanus, can also grow in zones four to eight. So choose wisely!
One important feature of ceanothus species is that they tend to be drought tolerant once fully established. Evergreen or deciduous, these plants are happier in full sunlight, but they can also grow in partial shade. If you live in an area with an extremely hot climate, then planting your ceanothus in partial shade would be a better option to avoid sunburn.
For newbie gardeners, growing a mass of pretty blooms in this rarest of blue colors might seem a little bit intimidating. But here is some good news – you do not have to be a green thumb to succeed in growing Californian lilacs. These flowering species are among the easiest to grow, as long as the conditions are right – moist, well-draining soil and a sheltered area with lots of sunlight. Ideally, you should choose a ceanothus cultivar that is suited to your local climate.
Causes of yellow leaves on ceanothus
So, you have just been enjoying the beautiful growth of your ceanothus when all of a sudden its leaves start turning yellow. This unsightly appearance can be both surprising and alarming, especially if you cannot identify the underlying cause.
There are several reasons your ceanothus shrub might develop yellow leaves, as summarized below:
1. Prolonged sunlight exposure
Extreme sunlight exposure can turn the leaves of your beautiful shrubs yellow. Sunburn, or leaf scorch, is a common issue, not just for ceanothus but almost any shrub or ornamental plant exposed to direct sunlight.
While sunlight is necessary for plants to photosynthesize, excessive heat and harmful UV rays can quickly dry their leaves through increased transpiration. The roots will not be able to meet the increased demand for moisture, which is why the leaves wilt, become pale, and develop burned spots. Thankfully, this issue can be resolved by transferring your plant to a spot with enough shade cover.
Do not move your ceanothus to full shade, however, as a lack of sunlight can also yellow its leaves. Try to position it where it can get the optimum amount of sunlight without burning its leaves or being totally deprived of light. On hot days, consider adding a shade cloth to protect your plant from the heat.
2. Too much water
Overwatering is another reason your ceanothus might produce yellow leaves. As you might know already, ceanothus is used to the dry climate of California, which is its native habitat. This means that water pooling around its roots can quickly drown the plant by cutting off the supply of oxygen to its roots. If the issue is not corrected right away, the excess moisture can cause the roots to rot and compromise the health of your entire plant, hence the yellowing leaves.
Other signs of overwatering include wilting, leaf drop, and stunted growth.
Your quick intervention is important to save your shrub from the ill effects of overwatering. If you have caught the issue in time, you simply need to stop watering immediately and give the soil time to dry completely. Use a soil moisture probe to accurately determine the dampness of the soil from now on, and water your plants only as needed. This will likely be more during summer than in winter.
3. Poor soil drainage
Poor soil drainage can have effects similar to those of overwatering. Even if you are not actually giving your plants too much water, the lack of drainage can cause water to pool in the soil and eventually drown the roots. Clay or compacted soil is especially problematic for your ceanothus, so make sure you choose your soil wisely!
One way to correct a drainage issue is to add sand or stones to improve the soil’s aeration. You may also consider using a tool like a digging fork or a plug coring aerator to amend the compacted soil in your garden before planting. Poke holes into the soil as deeply as you can to break up any compaction underneath and loosen the soil even more. Avoid walking or stepping on your garden bed as this can lead to compaction all over again.
Lastly, make sure that your shrubs are planted away from sprinkler systems or sloped areas such as at the bottom of a hill.
4. Root rot disease
Root rot is caused by soil-borne fungal pathogens that thrive in wet environments. It tends to be prevalent in overwatered plants, including ceanothus – even more so when the weather is warm and humid. Shrubs affected with this disease struggle with decayed roots that feel mushy and emit a foul odor.
Unfortunately, severe cases of root rot can be difficult to treat. As the disease progresses, your ceanothus will start to show several other signs such as wilting, dropping leaves, dieback of stems and foliage and, eventually, death. The fungal disease can also spread quickly through the soil, so it is very important to discard the affected plant immediately and apply soil treatments to prevent nearby plants from infection.
A lack of water can also cause leaf yellowing. Dehydrated shrubs will also lose their turgor and appear a bit sad and lifeless. The leaves may wilt, curl, and feel dry or brittle due to the lack of moisture.
But, unlike overwatering, underwatering is usually quite easy to reverse. Checking the soil regularly should provide a clue as to when your plants need a drink. Depending on your local climate, you should be watering your ceanothus thoroughly once every two to three weeks, or every time the soil starts to look dry. However, do not let the soil become bone-dry, or you risk damaging the root system.
6. Too much fertilizer
Yellow leaves can be a key indicator that your shrubs are struggling with overfertilization. In this case, you might also notice a white crust forming on the top layer of the soil. This condition is known as root burn, and aside from the yellowing leaves, it can also cause leaf deformities, wilting, stunted growth, and browning leaf tips.
The best way to treat overfertilization is to flush the excess nutrients out of the soil with water. Flood the soil thoroughly using a sprinkler or a garden hose, but make sure not to leave the soil too watery. Repeat the process every few days and let your shrub recover for about a month or so before feeding it again.
7. Summer leaf drop
The yellowing of your ceanothus leaves does not always mean trouble. If your shrubs are grown in the right conditions and you cannot identify any potential issues, then the yellow leaves could just be part of their natural growth cycle.
So, take a closer look at your plants. Are the yellow leaves mostly on the lower branches? Do the yellow leaves appear old and large, and evenly distributed throughout the foliage? Do you notice new leaves growing on the branches? If so, then your ceanothus is probably showing signs of summer leaf drop. This process is normal for most plants.
Shedding of the older leaves helps evergreens conserve their resources to make way for new, healthy leaves. You might notice your shrubs losing a few leaves occasionally, but not all at once.
If you are bothered by the unsightly yellow leaves, you can gently cut them off. Do not worry – cutting a few yellow leaves will not harm your plant. Otherwise, just leave your shrub alone and let it do its thing.
How do I fix yellow leaves on my ceanothus?
Yellowing of ceanothus leaves is mostly caused by improper watering, so consider correcting this issue first to save your shrub. Water your plant thoroughly and deeply, and let the soil dry out before watering again. Avoid planting it near a water source such as a sprinkler or drip hose, and make sure not to add too many moisture-retaining materials into the soil, like compost or mulch.
Adequate sunlight is important for ceanothus, too. These beautiful shrubs prefer a brightly-lit spot but without too much intense heat. If your local climate is too harsh for your ceanothus, consider using a shade cloth to protect its delicate foliage. Alternatively, plant it in a spot that gets filtered sunlight.
Some wall-trained ceanothus varieties can benefit from deadheading to maintain a tidy appearance and promote re-flowering. You can also prune your deciduous ceanothus in early spring for post-flowering shaping and size management. Just make sure not to overdo it, as most varieties do not tolerate hard pruning.
Ceanothus plants are easy to care for, but at times can still be susceptible to problems that cause their leaves to yellow. The cause is usually linked to improper watering or sunburn, although sometimes the yellowing may just be part of the plant’s natural shedding process. In the latter case, just sit back and let a few leaves drop naturally.
Image: istockphoto.com / Krzysztof Dac