If you want to grow hollyhocks in your garden and reduce the risk of rust, use these tips. Rust (a fungal disease) can be a big problem with hollyhocks and, while there is no solution, there are things we can do to slow it down.
Delphiniums are another favorite tall flower: see How to Grow Delphiniums for tips.
Growing Hollyhocks and Dealing With Rust
If you are big fan of old-fashioned hollyhocks in the garden but leery about problems like rust (a fungal disease), these tips will give you a fighting chance.
But, before we start, realistically speaking, rust problems may be slowed but not cured. Hollyhock rusts have been a global problem for hundreds of years and there are no known solutions, just best practices for discouraging them.
If you are a hardcore hollyhock fan like I am, it’s worth a try.
Old-Fashioned Hollyhocks and Fungal Diseases
The common name hollyhock is used for over 60 species in the mallow (Malvaceae) family. The ones we’re talking about here are cultivars of Alcea rosea: those tall, gorgeous cottage-style flowers, often with leaves like fig trees, providing an array of gorgeous pastel and bold colors, known for reseeding year after year.
While they are often deemed biennials (stems the first year, flowers in second year), some hollyhocks (Alcea rosa) are annual (full life cycle in one season) and others are “short-lived” perennials. The rust-resistant varieties recommended below are all perennial.
Rust is catch-all term for fungal diseases that affect various plants. Different rust species affect different plant families. The two most common hollyhock fungi are Puccinia malvacearum and P. heterogenea. There are several others as well. It can be hard to tell them apart but I’m not sure that matters.
When rust is present, you may first notice some spots on the leaves. These are teliospores that embed within the leaf. The underside may reveal pustules (yellow, orange, brown, purple, or black, depending on the timing) that gradually break down the foliage. When the infestation takes over, it disfigures the plant, and it’s time to pull the plug.
Can I Remove Rust with Fungicides?
Not really. Here’s the issue. These fungi spores are everywhere, not just on infected plants, and can travel great distances (hello, wind). Once they germinate, the horse is out of the barn.
Some gardeners may apply fungicides preventatively to (they hope) slow an outbreak, but, in my opinion, it’s a losing battle. You can treat the plant and the soil at its roots, but are you going to also get every spore in your garden and your neighbors’ gardens?
It’s unrealistic. And un-green.
A Realistic Approach to Growing Hollyhocks
So, what to do?
Start with rust-resistant hollyhock seeds (listed below). These are not pre-treated seeds but breeds that can be less prone to rust.
Keep in mind, though, that the same seeds growing in a warmer, dry, low-humidity garden in one region may go rust-free while succumbing to rust in a cooler, damper area. No fair!
We’re never going to be able to control or avoid hollyhock rust entirely, but with the tips listed below, you may be able to grow these gorgeous flowers with minimal or manageable amounts of rust.
I’m certainly going to give it another try.
6 Tips for Growing Hollyhocks and Dealing With Rust
1Start With Rust-Resistant Varieties
Some hollyhock seeds seem to resist fungi infections better than others so these are a good start.
Look for these two species:
- Fig leaf hollyhock (Alcea ficifolia) – sometimes called Antwerp
- Russian hollyhock (Alcea rugosa)
TIP: If you are buying starter plants, inspect them closely for any sign of spotting or spores. If you see signs of disease, do not buy from that source.
Happy Lights Hollyhock Mix Seeds
“The most rust-resistant Hollyhock around!”
- Zone 3-9 | Full Sun
- Biennial to short-lived perennial, flowers in second year, self-sows.
- Grow 5-7 feet tall, yes-containers, single-flowered, like well-drained soil, space 2-3 feet apart.
- Colors: shades of white, yellow, red, purple, pink, peach, burgundy and more.
- Chill seeds for 3 weeks before sowing. This can improve flower quality.
- Botanical Interests | Happy Lights Hollyhock Seed Mix They are not always available to check first. You can also find them at Parkseed.com and Selectseeds.com.
More Rust Resistant Hollyhock Seeds
- Alcea Ficifolia ‘Las Vegas’ | Source: Jelitto.com
- Antwerp Mixed Hollyhock (Alcea rosea subsp. ficifolia) | Source: Vesseys.com
- Spotlight Series (Alcea Rosea-Hybr.) | Blacknight, Mars Magic, Polarstar, Radiant Rose, Sunshine | Source: Jelitto.com
- Alcea Species: Eastern Turkey Hollyhock or Turkish Hollyhock Alcea hohenackeri | Source: Hardyplants.com (MN, USA)
2Grow in a Dry Location with Good Air Flow
You may notice hollyhocks growing rust-free in unusual places. I took the photo (above) in a laneway in a small town. Often it’s a sheltered location with good drainage, perhaps even somewhat drought conditions. That’s ideal for the plant and unfavorable for the fungus spores that need moisture to germinate.
Because of their height, hollyhocks look great at the back of a border or along a wall, but avoid sowing hear houses or sheds where they could be exposed to rain running off the roof or splashing.
Growing in containers is also an option, allowing us to move the plants as needed.
It’s tradition to let hollyhocks self-seed and grow in clusters but spacing the plants a few feet apart can also greatly reduce the spread of rust.
TIP: If you get some self-seeders, transplant them to pots, grow them to about 8-inches tall, and then transplant them back to the garden or a large container. They seem to do better with this extra care instead of transplanting directly.
3Water the Roots Not the Leaves
The rain will do what rain does and that’s not within our control, but, if you are hand-watering your hollyhocks, aim for the soil only (no splashing), and leave the plant dry.
It can also help to water earlier in the day to allow the midday sun to evaporate any excess water.
4Remove Rust-Infected Leaves Immediately
Check your plants regularly. Rust usually appears on the lower leaves first, spreading upward, which is why it’s easy to miss until it’s too late: once it’s at eye level, the poor plant may be heavily infected.
If you do see those dreaded rust spots, act immediately.
For a few rust spots, remove the infected leaves. If it’s really bad and you have other plants that could get infected, cut the plant down to just above the ground. If the hollyhock has not yet flowered or produced seeds, it will have the energy to do so next year. I’ve listed suggestions for disposal below.
I know gardeners (super hollyhock fans) who manage the situation by keeping the least infected plants and removing the rest. Sometimes leaf removal is enough to slow the rust long enough to enjoy the flowers and get seeds.
While the embryo of hollyhock seed has not been shown to carry the fungus, the flower parts where the seed grows might.
For this reason it’s often advised not to save seeds from infected plants. You can decide this one for yourself.
Hollyhock rusts are not a threat to other plants outside the Malvaceae family, so do not worry about that. There are plenty of other specialty rusts to wreak havoc on roses, Pelargoniums, chrysanthemums and more!
What Should I Do With the Rust-Infected Plants?
‘Rapid composting’ is often recommended. This means placing the plants in a hot compost pile where the high heat will break them down and kill the spores. A cold compost pile will likely just keep the spores dormant until you stir them up.
I could not find research stating the temperature that kills the spores but 145F tends to be the minimum for other microbials.
Some advice says to bury the infected plant matter in other leaves, letting the good microbes and beneficial fungi spores take over.
Others suggest burning the diseased matter if permitted (or desirable) where you live.
5Remove Other Susceptible Plants
It’s not always realistic (or desirable) to remove vulnerable plants but it is something to consider. (Do as I say, not as I do!)
Puccinia malvacearum can infect all members of Malvaceae family. If an outbreak is really severe, in addition to cutting back or removing your hollyhocks, consider removing other plants in the same family (including weeds). I’ve listed a few here:
- Abutilon – Flowering Maple, Indian Mallow
- Alcea and Althaea – Hollyhock
- Giant Mallow – such as Rose-of-Sharon (H. syriacus)
- Hibiscus – Rose Mallow
- Lavatera – Tree Mallow
- Malva – Mallow, Musk Mallow
- Malvastrum – False-mallow
- Sphaeralcea – False Mallow
If it’s really bad, stop growing them, give it a few years (or more) and try again.
6Cut Hollyhocks Down the Ground in Fall
If your plants made it through the growing season without rust: congratulations! You are a unicorn.
If there was some rust, cut the stalks down to the ground and dispose of the diseased material.
Otherwise those fungal spores stay dormant in the winter, ready to pounce again in spring.
Frequently Asked Questions
1My hollyhock is not flowering. What is wrong?
Hollyhocks need full sun to flower: are yours getting at least six hours of direct sun each day?
Another common cause is too much fertilizer, specifically nitrogen (the N in N-P-K on fertilizer labels). Depending on how far along you are in the season, you may not be able to get blooms this year. But stop fertilizing, regardless.
There is also a fungus, Botrytis, a gray mould, that infects flowers and buds that could be to blame.
2If I save seeds from a rust-infected hollyhock, will the new plants have rust?
As far as we know, the seed embryos do not carry rust but the plant parts surrounding the seed might.
For this reason, it is not recommended to save the seeds from infected plants.
It’s one tiny preventative step in a spore-filled world.
You may also want to read up on the surface sterilization of seeds using a bleach solution in case that helps.
So, have I scared you off or will you try growing hollyhocks? When they succeed, they are well worth it.
- Hollyhock Rust | Plant Clinic – Cornell
- Hollyhock Rust | Pest Control – Michigan State University
- Hollyhock Rust Help for Backyard Gardeners | Missouri Botanical Garden
- Common Hollyhocks Pests | Burpee
~Melissa the Empress of Dirt ♛