How to Grow and Care for Blackhaw Viburnum

Blackhaw viburnum (Viburnum prunifolium) is a deciduous shrub with an upright growth habit, almost growing as wide as it is tall. It can be trained to grow as a small tree with a single trunk. Its rough bark is a reddish-brown color, and it sports ovate, glossy dark green leaves that stretch about 4 inches long. In the late spring, clusters of small white flowers appear, followed by yellow berries that mature to a blue-black color. Birds and other wildlife are attracted to these fruits. In the fall, the foliage turns to shades of red and purple. This shrub grows at a moderate rate and is best planted in the early spring or fall.

Blackhaw Viburnum Care

Blackhaw viburnum is a low-maintenance shrub that grows well in many different locations and climates. Selecting a spot for your shrub that has good soil drainage and ample sunlight is key to making its care a breeze. Make sure to account for the shrub’s mature size to give it enough space when planting. 

This shrub is quite hardy and doesn't typically have any serious issues with pests or diseases. It has a good tolerance for pollution, as well as for being planted near black walnuts and other walnut tree species, which release a substance that’s harmful to many plants. In terms of its regular care, plan to water during dry spells and feed your shrub annually. Pruning also is typically an annual chore to maintain the shrub’s size and shape. 

Light

This shrub prefers to grow in full sun or partial shade, meaning it needs at least three hours of direct sunlight on most days. The best flowering and fruiting will occur in higher levels of sunlight. However, it's ideal to provide the shrub with some afternoon shade in the hottest parts of its growing zones. 

Soil

Blackhaw viburnum will tolerate a variety of soil types as long as it has good drainage. It thrives in loamy soil but also can handle sandy or clay soil. Moreover, it prefers a neutral soil pH but can tolerate slightly acidic to slightly alkaline soil as well.

Water

This shrub has moderate water needs. Keep the soil for young shrubs evenly moist (but not soggy) as they establish their root systems. Mature shrubs have some drought tolerance and generally will only require watering if you have a prolonged period without rainfall and/or are experiencing hot temperatures. 

Temperature and Humidity

Blackhaw viburnum is hardy both to hot and cold temperatures. It can tolerate temperatures around 90 degrees Fahrenheit as long as its moisture needs are met. And it will survive conditions below freezing, though once frost hits in the fall is when it starts to lose its leaves for winter. Humidity typically isn’t an issue for the shrub. In very high humidity it’s important to ensure good air flow around the plant to prevent fungal diseases. And in dry conditions, a layer of mulch over the root zone can help to retain soil moisture.

Fertilizer

The shrub will benefit from an annual feeding in the spring, especially if you have poor soil. Use a balanced, slow-release fertilizer around the plant, following label instructions. 

Types of Blackhaw Viburnum

There are several varieties of blackhaw viburnum, including: 

Viburnum prunifolium 'Guazam’: This shrub grows slightly smaller than the main species plant and features dark green leaves that turn crimson in the fall. 

Viburnum prunifolium 'McKrouge’: This variety also is slightly smaller than the species shrub, and its foliage turns a maroon color in the fall.

Viburnum prunifolium 'Summer Magic’: The foliage on this variety emerges a reddish-pink color and turns yellow to red in the fall.

Pruning

Prune your shrub right after it’s done flowering. Buds for the next year start forming in the summer, so there’s only a small window after the shrub’s spring bloom when you won’t accidentally remove some of next year’s flowers via pruning. The shrub has a somewhat irregular shape, and by letting it take its natural shape you won’t have to do much pruning to keep it tidy. Thin out stems that are growing very close to one another to improve airflow throughout the shrub and allow sunlight to hit all parts of it. And only slightly prune the tips of the stems if you wish to control the shrub’s size, as heavy pruning can damage its form. Remove any dead, diseased, or damaged portions as they arise. 

Propagating Blackhaw Viburnum

You should propagate blackhaw viburnum in early spring to create new plants. Make sure to choose a healthy plant free from disease. You can propagate blackhaw viburnum by cuttings. Here’s how:

1. Take 4 to 6 inch cuttings in late fall after leaves have dropped or in spring using a sharp instrument.
2. Remove leaves from the bottom of the cutting and keep the cutting moist.
3. Mix one part peat and one part perlite and plant the cutting leaving half out.
4. Cover with plastic. Keep the pots in indirect light and mist occasionally.
5. Check for rooting in approximately four weeks.

How to Grow Blackhaw Viburnum From Seed

Plant seeds in small pots in early spring. Make sure to keep them lightly moist and in a bright and warm spot. Once the seedlings are about one foot tall, you can transplant them outdoors. Here's how to plant blackhaw viburnum from seeds:

1. Save seeds by harvesting the fruit once it turns its black-blue color and drying the berries (with pulp) in a cool location.
2. Once dry, store the seeds over the winter in a brown paper bag in a cool, dark spot.
3. Plant them in small pots in the early spring in a seed-starting mix that you keep lightly moist.
4. Keep the pots in a bright, warm spot as they germinate.
5. Transplant the seedlings outdoors when they're about a foot tall. Make sure to bring the young plants outside for gradually longer stretches for about a week to acclimate them to direct sun.

Overwintering

To prepare your shrub for winter, cut down watering in the fall. You can also add mulch to the base of the plant to help insulate it. Loosely cover with burlap if snow or heavy winds are expected.

How to Get Blackhaw Viburnum to Bloom

Blackhaw viburnum blooms in late spring with small, white flower clusters which gave way to berries in the fall. Full sun and well-drained, acidic soil help encourage blooming. Make sure not to trim while dormant as you may lose the flower-producing buds. Once blooming, make sure to provide the plant with afternoon shade. Deadheading is not necessary as the flowers give way to fruit.

Common Problems With Blackhaw Viburnum

This shrub is relatively easy-going, but there are a few common issues to look out for. It's particularly prone to root rot, but this is easily preventable if you know how to properly care for it.

Root Rot

Armillaria root rot is one of the most common afflictions blackhaw viburnum is prone to. The fungus affects the roots of the plant and will turn the leaves yellow and cause them to drop. To avoid this, make sure the plant has proper air circulation and is not overwatered. Soil should also have ample drainage.

Leaf Mildew

You may notice something white and dusty on the leaves, which is known as powdery mildew. In this case, apply a fungicide. To prevent mildew, avoid overwatering and ensure adequate air circulation around the plants..