Ilex Shamrock dying - Ask Extension
In the last four years, I have twice planted 6 Ilex bushes in my front garden. I lost 5 of the 6 the first time and now again 5 of the 6 this year....
Knowledgebase
Ilex Shamrock dying #722326
Asked September 09, 2020, 12:42 PM EDT
In the last four years, I have twice planted 6 Ilex bushes in my front garden. I lost 5 of the 6 the first time and now again 5 of the 6 this year. They are planted with southern exposure. When planted, I have given them daily watering. Both times they were planted in late spring. They make it through the summer, fall and winter and into the next spring season. This year especially, they received every evening watering except when rain was expected. The turn is almost overnight. By the time I see the brown leaves, they are all going down hill to dying.
Anne Arundel County Maryland
Expert Response
Shamrock Inkberry (Ilex glabra 'Shamrock') is a relatively wet-tolerant holly, but may not prosper when kept too wet. Southern exposures are not problematic, but over-watering or planting too deeply can lead to root suffocation and infection (rot) which results in death of the top growth. While we do not know what volume of water you were giving the plants each time, daily watering (especially in evening, when evaporation is minimal) sounds excessive. A morning soaking once or twice a week in hot, dry weather is more typical of what most new plants would need; perhaps three times a week if the soil drains very quickly and rain is scarce. Were they being watered by hand, or are they on a timed sprinkler or drip-watering system?
Here is our page on watering guidelines for trees and shrubs, if it is helpful for future reference: https://extension.umd.edu/hgic/topics/watering-trees-and-shrubs. A major component of watering well is through monitoring - physically checking the soil prior to watering rather than assuming a plant needs water based on a schedule or the weather.
Once the foliage browns this thoroughly, the plants are unsalvageable, as you have noticed. Stress can also make the shrubs more susceptible to an above-ground fungal infection called Botryosphaeria, though typically this affects only a few branches at a time and usually this results from drought. In general, however, the dieback symptoms (complete foliage browning on the affected branch) will be the same. If this infection were present, all that could be done would be to prune away dead branches; here, of course, this is impractical because all of them have died.
Aside from drowning roots outright, another risk of over-watering is infection from a pathogen called Black Root Rot (Thielaviopsis), to which Inkberry and some of its relatives are vulnerable. There is no homeowner treatment for the disease, which takes advantage of wet soils and stressed plants. While the fungus prospers in relatively cool soil, its effects in depriving the plant of moisture (because it's killing the roots) may not be seen until water demands from the foliage are higher in summer.
Planting shrubs and trees too deeply can cause health issues with roots. The point at which roots begin to branch off of the trunk should sit at or just below the soil surface. If buried by a few inches more soil, problems can arise, even if it takes them months to manifest. Shrubs and trees often become buried too deeply in their nursery pots, so inspect root balls after they are removed from the pot prior to planting. Similarly, roots need to be disentangled if they were matted together around the pot edges. If not done, this will hamper the roots' ability to establish into your soil, as well as create water drainage issues because the soil inside the root ball is very different than the soil in the garden. In this situation, it is much easier for one soil type to stay too wet and the other too dry; which will be which is difficult to predict, but neither is a good scenario when roots are trying to establish.
If you try again this year, early fall is a fine time to plant evergreen shrubs; late fall (after about mid-October) is risky as evergreens are at greater risk of desiccating since they have less time to establish roots before the soil becomes too cold. For spring, earlier in the season (March) would be better than later, so they can settle-in during weather that brings more regular rains and requires less monitoring for watering needs as a result. Even though these Inkberries survived their first summer in the ground, that may have been when their stress began, only reaching the tipping-point of tissue damage the following summer.
The problem is likely preventable in the future if planting guidelines and a different watering regimen are followed, but if you are leery of trying Inkberry again or are afraid that root rot or other pathogens are at work, then consider alternative shrubs for this location.
Miri
Here is our page on watering guidelines for trees and shrubs, if it is helpful for future reference: https://extension.umd.edu/hgic/topics/watering-trees-and-shrubs. A major component of watering well is through monitoring - physically checking the soil prior to watering rather than assuming a plant needs water based on a schedule or the weather.
Once the foliage browns this thoroughly, the plants are unsalvageable, as you have noticed. Stress can also make the shrubs more susceptible to an above-ground fungal infection called Botryosphaeria, though typically this affects only a few branches at a time and usually this results from drought. In general, however, the dieback symptoms (complete foliage browning on the affected branch) will be the same. If this infection were present, all that could be done would be to prune away dead branches; here, of course, this is impractical because all of them have died.
Aside from drowning roots outright, another risk of over-watering is infection from a pathogen called Black Root Rot (Thielaviopsis), to which Inkberry and some of its relatives are vulnerable. There is no homeowner treatment for the disease, which takes advantage of wet soils and stressed plants. While the fungus prospers in relatively cool soil, its effects in depriving the plant of moisture (because it's killing the roots) may not be seen until water demands from the foliage are higher in summer.
Planting shrubs and trees too deeply can cause health issues with roots. The point at which roots begin to branch off of the trunk should sit at or just below the soil surface. If buried by a few inches more soil, problems can arise, even if it takes them months to manifest. Shrubs and trees often become buried too deeply in their nursery pots, so inspect root balls after they are removed from the pot prior to planting. Similarly, roots need to be disentangled if they were matted together around the pot edges. If not done, this will hamper the roots' ability to establish into your soil, as well as create water drainage issues because the soil inside the root ball is very different than the soil in the garden. In this situation, it is much easier for one soil type to stay too wet and the other too dry; which will be which is difficult to predict, but neither is a good scenario when roots are trying to establish.
If you try again this year, early fall is a fine time to plant evergreen shrubs; late fall (after about mid-October) is risky as evergreens are at greater risk of desiccating since they have less time to establish roots before the soil becomes too cold. For spring, earlier in the season (March) would be better than later, so they can settle-in during weather that brings more regular rains and requires less monitoring for watering needs as a result. Even though these Inkberries survived their first summer in the ground, that may have been when their stress began, only reaching the tipping-point of tissue damage the following summer.
The problem is likely preventable in the future if planting guidelines and a different watering regimen are followed, but if you are leery of trying Inkberry again or are afraid that root rot or other pathogens are at work, then consider alternative shrubs for this location.
Miri
