Elizabeth is a Permaculture Garden Designer, Sustainability Consultant and Professional Writer, working as an advocate for positive change. She graduated from the University of St. Andrews with an MA in English and Philosophy and obtained a Diploma in Applied Permaculture Design from the Permaculture Association.
Reviewed By PETER LICKORISH
Peter is a Horticulture Lecturer and self-employed Horticulturist, with a passion for diverse areas of the industry - from garden design to the science behind plant growth and propagation. He has completed the Royal Horticultural Society’s Master of Horticulture (MHort) Award and lectures on RHS courses at Bedford College.
Hollyhocks are cottage-garden favourites and attractive short-lived perennials that flower in the second year after sowing.
Unfortunately, these pretty flowering plants are highly susceptible to a fungal infection – a disease known as hollyhock rust.
When growing hollyhocks, you are likely to see this infection, especially during damp years, as it is, sadly, very common.
What Is Rust?
Hollyhock rust is a fungal infection caused by Puccinia malvacearum.1Hollyhock rust. (n.d.). Royal Horticultural Society. Retrieved March 27, 2023, from https://www.rhs.org.uk/disease/hollyhock-rust
Spread by airborne spores, this infection develops very frequently on hollyhocks grown in organic gardens.2Hollyhock Rust. (n.d.). Wisconsin Horticulture. Retrieved March 27, 2023, from https://hort.extension.wisc.edu/articles/hollyhock-rust/
It is especially prevalent in years when the summer weather is wet.
The rust fungi are known as biotrophs and they reside within the living plant tissue of hollyhocks and extract nutrients from the plant’s cells.3Duplessis, S., Cuomo, C. A., Lin, Y., Aerts, A., Tisserant, E., Veneault-Fourrey, C., Joly, D. L., Hacquard, S., Amselem, J., Cantarel, B. L., Chiu, R., Coutinho, P. M., Feau, N., Field, M. A., Frey, P., Gelhaye, E., Goldberg, J., Grabherr, M., Kodira, C. D., . . . Martin, F. (2011). Obligate biotrophy features unravelled by the genomic analysis of rust fungi. Proceedings of the National Academy of Sciences of the United States of America, 108(22), 9166–9171. https://doi.org/10.1073/pnas.1019315108
Hollyhock rust will not quickly kill plants outright, but a heavy attack can certainly weaken plants, causing tissues to collapse and die in extreme cases.
Rust is easy to see and presents as little orange or yellowish dots on the stems and leaves.
These typically begin low down on the plant and spread upwards.
Leaves that are severely affected will begin to shrivel and even though a little rust can leave the plants largely unharmed, they will likely be somewhat stunted and not grow or flower as well.
Preventing Rust On Hollyhocks
Unfortunately, when growing hollyhocks, it is very unlikely that you will be able to avoid rust altogether.
Rust arrives on the wind, as spores blow in from neighbouring gardens or wild plants growing in the area.
It can also arrive with seeds, if the batch includes debris from bracts or other flower parts, or in hollyhock plants that are purchased.
These plants may not show any symptoms yet, but might carry rust within.
“I regard hollyhock rust as the inevitable price to pay for their wonderful blooms, but it is pretty much the only price to pay,” explains Master Horticulturist Peter Lickorish.
“Otherwise, they are rugged beauties!”
Therefore, rust is difficult, if not impossible, to escape entirely, but there are ways that you can reduce the chances of a severe rust infection taking hold.
To reduce the chances of rust being severe on your hollyhocks you can:
- Select a spot with lower humidity, where the plants are somewhat protected from damp summer conditions. The base of a stone wall, in a rain shadow or under some cover can be good spots, as long as there is still access to the full sun these flowers require.
- Make sure that there is plenty of airflow around your plants. Congestion and overcrowding can make this fungal problem worse. Make sure that you avoid planting too densely.
- Ensure that the soil is healthy, rich in organic matter and neither too wet nor too dry. This will keep plants in better health, with stronger roots, and may reduce the severity of an attack.
- Avoid growing other susceptible plants close by, such as other mallows, lavatera and sidalcea, and do not let wild common mallow grow too close to your prized hollyhocks.
- Grow hollyhocks as a biennial and discard them after flowering. Though these are short-lived perennials that can bloom more than once, those which have lived past their second year are more likely to get rust.
Of course, you should also check plants regularly for signs of this issue so that you can act quickly if required to prevent the problem from getting particularly severe or from spreading more rapidly through your garden.
Hollyhock Rust Treatment
Vigilance is key when it comes to making sure that a rust infection does not bring down your hollyhocks.
As mentioned above, rust can be problematic when severe, but a milder case will only be unsightly and you should still get some flowers.
From the very beginning of the season, you should keep a close eye on your hollyhocks so that you can react quickly the moment that rust is detected.
If you spot rust on the lower leaves of hollyhocks, remove and dispose of these right away before the problem has a chance to spread.
If a plant is particularly badly infected with rust, then it is, unfortunately, best to dispose of that plant altogether carefully, keeping it well away from your compost heap.
Fungicides
For severe rust, fungicides may have to be applied.
Tebuconazole and triticonazole are approved for the control of rust on ornamental plants and may prove effective.4How do you manage rust on hollyhocks? (2023, March 30). University of Maine Cooperative Extension. Retrieved May 24, 2023, from https://extension.umaine.edu/gardening/2023/03/30/how-do-you-manage-rust-on-hollyhocks/
However, they may need regular applications, especially during wet weather.
Some hollyhock varieties are now showing improved resistance to rust and may well be worth pursuing.
Alternatively, you can also grow shorter plants in front of your hollyhocks so that you cannot see the unsightly problem as the season progresses.
You should still see a few flowers – as long as the rust problem has not become too severe.
