This article delves into the intriguing world of flower coloration in Alcea rosea L. ‘Nigra,’ or black hollyhock. While the allure of “black” flowers has long captivated gardeners, it’s well-documented that many such blooms are, in reality, dark shades of purple. The black hollyhock is a popular choice among gardeners who want to add a touch of intrigue and contrast to their flower beds.
Botanical Information about Black Hollyhock
Black hollyhock, scientifically known as Alcea rosea ‘Nigra,’ is a striking and unique variety of hollyhock known for its deep, dark purple to nearly black flowers. Hollyhocks are tall, biennial, or short-lived perennial plants beloved in gardens for their tall spires of colorful, funnel-shaped blooms.
Here are some key characteristics and care tips for black hollyhocks:
The defining feature of the black hollyhock is its very dark purple, almost black, blossoms. These flowers can create a stunning contrast when planted alongside lighter-colored flowers in the garden.
Black hollyhocks typically bloom in the summer months, producing a profusion of dark flowers on their tall stalks.
It is best to grow black hollyhocks in full sun. Ensure that they receive at least six to eight hours of direct sunlight each day when planting them.
Black hollyhock plants demand soil that is well-drained and rich in organic matter to flourish. They are somewhat tolerant of different soil types but perform best in soil that retains moisture without becoming waterlogged.
Hollyhocks need regular watering, especially during dry periods. Ensure the soil remains consistently moist, but avoid overwatering, which can lead to root rot.
To ensure enough air circulation, it is recommended to plant space black hollyhock plants at a distance of 18-24 inches from each other.
Summarizing the General Information of Hollyhock (Alcea rosea):
|Plant Name||Hollyhock (Alcea rosea)|
|Origin||Native to China|
|Varieties||Annual, biennial, perennial|
|Height||1.5–2.7 meters (5–9 feet)|
|Stem Growth||Almost straight|
|Leaves||Five to seven lobes|
|Flower Colors||White, pink, red, yellow|
|Flower Size||7.5 cm (3 inches) or more|
|Flower Placement||Borne along the stem|
|Invasive Potential||Considered invasive|
Pruning And Support
Deadhead spent flowers to encourage continuous blooming and prevent self-seeding, as hollyhocks can become invasive if not managed. However, due to their height and the weight of their blossoms, hollyhocks may require staking or support to prevent them from toppling over.
Black hollyhocks are usually biennial, meaning they complete their life cycle over two years. In the first year, they grow foliage, and in the second year, they bloom and produce seeds. After flowering, they will often die back in colder climates but may self-seed and return in the following year.
Hollyhocks, including black hollyhocks, are susceptible to rust, a fungal disease that affects their appearance. Key points to manage rust include:
Understanding the Common Hollyhock Disease
Hollyhocks, also known as Althaea rosea, are often plagued by rust, caused by the “fungus” Puccinia malvacearum. This widespread disease was first identified in Chile back in 1852. When hollyhocks get severely rusted, their leaves turn yellow, wither, and fall off prematurely, making the plants look untidy. However, rust-infected hollyhocks rarely die from the disease. Interestingly, rust tends to be a big problem in spring and autumn but less so in the middle of summer, especially during dry periods.
Hollyhock rust symptoms begin as lemon yellow to orange, almost waxy growths primarily on the undersides of lower leaves. Over time, these pustules turn reddish brown to chocolate brown. Bright yellow to orange spots with reddish centers also form on the upper leaf surface opposite these growths.
The rust quickly spreads to other leaves, covering them with small reddish-brown to chocolate-brown pustules filled with numerous microscopic dark brown spores (teliospores). While mainly found on the undersides of leaves, these pustules can also appear, though to a lesser extent, on the upper leaf surfaces, petioles, stems, and flower bracts.
Hollyhock rust has a cycle that starts with the fungus overwintering in young shoots and as mature teliospores on various plant parts, including seeds and bracts. In spring, it releases spores carried by air and rain, infecting the hollyhock through its outer layers.
For about 8 to 10 days, the fungus spreads inside the plant. Then, it forms a cushion-like structure under the plant’s skin, which eventually bursts through, continuously releasing teliospores. These new spores can infect healthy hollyhocks or other plants nearby.
In humid conditions, the rust spreads from leaf to leaf until the whole hollyhock plant gets infected and loses its leaves one by one.
Effective control measures for hollyhock rust include
To prevent hollyhock rust, prune infected parts after flowering, remove common mallow, and dispose of early rust-affected leaves in spring. Use fungicides during new spring growth if necessary.
Remove and Destroy Infected Plant Parts
After the flowering season, promptly gather and dispose of all rust-infected hollyhock leaves and stems. These can be burned, buried in a compost pile, or taken away with the trash. Cut the plants at ground level and remove all fallen leaves and stalks.
Eliminate Common Mallow
Get rid of common or round-leaf mallow (Malva rotundifolia) plants, as they can harbor the rust fungus over winter, potentially infecting hollyhocks in the spring and early summer.
Remove Early Rust-Affected Leaves
In the spring, remove and discard the first leaves that show signs of rust.
When sanitation measures aren’t enough, consider using fungicides. Start applying them when new spring growth begins. Ensure complete coverage of all aboveground plant parts with a fine mist or dust. Make 5 or 6 applications spaced 7 to 10 days apart, using a recommended fungicide-water mixture.
To propagate hollyhocks from seeds, let the seeds be mature enough for harvesting or wait for the time when the seeds fall down. Prepare well-draining soil, plant seeds, keep the soil moist for germination (2-8 weeks), then transplant the seedlings into the ground directly.
Black hollyhock, with its striking dark blossoms, adds an enchanting touch to garden landscapes. Understanding its unique characteristics and care requirements is key to cultivating these intriguing flowers successfully. However, ensure the health and vitality of your black hollyhocks by following these guidelines for nurturing and managing rust, allowing you to enjoy their captivating beauty in your garden.