Identifying & Treating Hollyhock Diseases And Pests

Hollyhocks are gorgeous flowers that look perfect in country landscapes or cottage-style gardens. Prized for their height and showy blooms, hollyhocks form many clusters of petunia-shaped or carnation-type flowers on tall, upright stalks.

They can grow up to eight feet or more in height, and flowers come in various shades of red, orange, yellow, pink, purple, white, and even black. Some cultivars are bi-colored and have the appearance of common hibiscus flowers, which makes sense since they are both in the mallow (Malvaceae) family.

Most varieties of hollyhocks are biennials or short-lived perennials, so blooms won't show up until the second season. They are prolific self-seeders, however, and new plants will likely arrive without intervention.

While these beauties are easy to grow and care for, they are susceptible to certain problems. We'll go over how to identify and treat hollyhock diseases and pests so you can keep your country chic garden looking its best.

Benefits of Hollyhock

Many gardeners plant hollyhock not realizing that the entire plant is edible. Roots, leaves, seeds, and blossoms can all be used, though the hairy stem may not be as palatable to some.

Young leaves and flower petals can be eaten raw or cooked to relieve some of the bitterness, either added to salads or used in stir-fries. Flowers are also known to relieve dry skin, and they can be added to baths or applied to your skin.

Hollyhock is related to marshmallow root (the perennial plant, not the snack), which is an herbal remedy often used to relieve inflammation, pain, urinary tract problems, stomach issues, and various symptoms of upper respiratory infections.

Hollyhock can be used instead of marshmallow root as a milder remedy in the form of a cold tea, or leaves can be made into a poultice.

They're beneficial in the garden, as well, as they lure pollinators of all kinds to vegetable patches, helping them thrive by promoting biodiversity and pollination. Their height can be useful for shading smaller plants that aren't tolerant of afternoon sun, or to help to fill in and decorate spots along fences and walls.

They make for great cut flowers, often as the focal point in a centerpiece, along with shasta daisies, coneflowers, dahlias, zinnias, Annabelle hydrangeas, and other midsummer bloomers.

Where to Plant Hollyhock

Hollyhocks love full sun, just like other prolific bloomers. Pick a spot that receives at least six hours of full sun and make sure it's protected from any heavy winds.

Planting hollyhocks against fences, walls, buildings, trellises, or among other tall plants will protect them from bending over, which is one of the structural issues with hollyhock. They can tolerate part shade but will become too flimsy in full shade.

Otherwise, hollyhocks are deceptively tough and can tolerate a variety of other conditions, including hot, dry weather, and various soil types. As long as it's protected from high winds and has full sun, this plant will thrive anywhere.

To get the most blooms, however, plant in nutrient-rich, well-draining soil, and not overly wet soil. Don't worry about pH levels.

Since there are many varieties with different bloom times, the best way to fertilize will depend on the cultivar, though generally speaking, adding fertilizer in the spring is recommended as many set flowers in June and July.

Hollyhocks are hardy in zones 3-8, but always check the plant tag for specific zone requirements. A thick layer of mulch will protect them in extremely cold weather and help to retain moisture in the summer.

Although these plants are naturally tough, they can, unfortunately, succumb to certain types of disease.

Rust

A major problem with hollyhocks is a fungal disease called rust which can survive on infected plant parts from year to year.

Rust is a very common infection that's caused by the fungus Puccinia malvacearum.

The first sign of a rust infection is reddish brown spots on the underside of leaves near the bottom of the plant. The top side of the leaf can show a larger orange or yellow spot, sometimes with a red center.

The more spots there are, the more chlorophyll is destroyed and misplaced. Hollyhock growth will appear deformed and stunted. In severe cases, hollyhock leaves will begin to fall off.

How to Prevent Rust

You can help to prevent rust infection by ensuring the plants have good ventilation at their planting site. This can be a bit of a catch-22 since you also want to protect hollyhocks from strong wind.

Avoid planting hollyhocks too close together, as crowding causes high humidity and low air circulation, which is the perfect breeding ground for rust. This way, you can keep them out of the wind, while still allowing for natural breezes to clear any stagnant air.

Another important practice is to water directly into the soil instead of spraying plants with hoses or sprinklers. Avoid getting the plant wet as much as possible, as rust spores can attach easier to damp, wet leaves.

Hollyhocks are tolerant of many soils except overly wet soil conditions. This kind of soil can weaken your hollyhocks and make them more susceptible to rust. New plants need to be well-watered in the first season, but make sure there is good drainage.

How to Treat and Remove Rust

If you notice that rust has started on your hollyhocks, there are a few tactics for getting rid of it. The first thing you should do is remove any infected leaves immediately.

Use sharp pruners, and make sure to disinfect them with bleach afterward. Dispose of any infected foliage into a sealed bag to prevent the spread of the infection.

Do not add infected parts to compost piles or organic bins, and never leave infected foliage on the ground, as even dead leaves can continue to infect other plants and attract rust.

The other thing to remedy a rust infection is to use topical fungicides. There are some commercially available for treating rust specifically, and these usually contain sulfur or copper. Note, that some products aren't recommended in hot weather, so always follow manufacturer instructions.

While fungicides may help, prevention and removal of infected leaves are the best approach. Rust doesn't usually kill the plant, so plan on prevention for the next season to get ahead of the problem.

If a large enough infection occurred and spread throughout the garden, it may be best to cut back and remove all of the infected plants, and start new the following year.

Weevils

Hollyhock weevils are tiny insects that overwinter in the soil of hollyhock beds and emerge in the springtime. They are a dark grey color with orange or reddish legs, usually growing to about 1/8 inch in length which includes their long "proboscis" or snout (the female's is larger than the male's).

These insects bore into leaves and stems, and then feed on and lay eggs mainly in the flower buds of hollyhocks.

Flowers will still form, but the egg remains embedded in the seed pod. Since the larvae feed on the seed pods, this interferes with the plant's ability to self-seed. Larvae then pupate and become adults that drop back into the soil late in the summer.

If you notice weevil action early on, destroy any seed pods that are forming. Sadly, you'll lose seeds for next year, but this is one of the best ways to eradicate the larvae stage and stop the weevil cycle.

How to Identify and Treat Weevils

Weevil damage is identified by the small holes you'll see in the plant, and while mainly aesthetic, the damage can disrupt not only the self-seeding process but also the quality and lifespan of the plant.

Since hollyhocks are biennial or short-lived perennials, weevils can put a damper on gardeners' expectations for lots of blooms.

Unless massively infected, a plant can survive a weevil attack—though the flowers, if they survive, will be damaged. For cases of light infestation, place a cloth underneath your hollyhock and shake it vigorously to dislodge the weevils, and then quickly dump them in a bucket of soapy water.

Introducing beneficial nematodes into the garden can help to kill them off. Nematodes can be bought at garden supply stores or ordered online.

Insecticidal soap can also be effective against weevils, but specific pesticide that targets weevils is the only solution for extreme infestations, especially ones that recur yearly.

Cut Worms

Cutworm is the name used for the larvae of many types of moths. They can grow as long as two inches, and come in a variety of colors ranging from grey to pink, green, and black.

They tend to be active only at night, doing their damage quietly and unseen. When they are not moving, they will typically be curled up.

They're active in early spring and do the most harm to newly emerging plants. Unfortunately, once they've made it onto your hollyhock plant, the damage is usually irreversible.

Cut worms will eat the leaves between the veins, turning them into skeletons, or may even destroy the tops of plants, and entire root systems.

Mature hollyhocks are not very attractive to cutworms, but you should protect any new seedlings or growth until you know that these pests aren't a problem.

How to Prevent and Remove Cut Worms

Because cutworms travel across the surface of the soil, you can erect a fine mesh barrier underneath plants, or place cardboard on the soil to keep them off new plants.

BT (Bacillus Thuringiensis) is a biological control that will paralyze the cut worm's intestinal tract, but while this pesticide is effective, it's extremely harmful to beneficial insects as well as overall soil health, and is not recommended as organic pest control.

Use nematodes or sprinkle diatomaceous earth over the top of the soil instead. If you find that cutworms are a problem in your garden, remove all spent plants after the growing season, and cultivate the soil in the fall and spring.

Slugs and Caterpillars

Slugs and caterpillars are another kind of pest that wreak havoc on all kinds of plants, including hollyhocks. They won't specifically target hollyhocks, but if you have a slug and caterpillar infestation, they won't be spared, either.

Slugs are slimy and slow creatures that can be easily killed off by sprinkling table salt on top of them. If numbers are small, or you only see a few here and there, the plant will be able to cope with any minor damage, so best leave them be as natural predators will happily dine on them.

Caterpillars are a different story. Unless you can identify the caterpillar as an unwanted creature, it is best to leave them alone as they often turn into beautiful butterflies and moths that are beneficial to gardens and ecosystems.

The best way to know whether you have problematic caterpillars is to learn how to identify them properly. Get to know the species in your area and check with local gardening groups or Universities to see what types of caterpillars are harmful and the best ways to get rid of them.

While hollyhocks are generally hardy plants, it's important to learn how to identify and treat common hollyhock diseases and pests. Plant in full sun, protect them from heavy winds, and be proactive about checking for problems.

Hollyhocks are bountiful bloomers with many different cultivars to meet the aesthetic needs of your garden. While most are short-lived, their prolific seed-spreading means you can have a garden full of them for years to come: as long as you can keep them healthy.