Black locust (Robinia pseudoacacia)

Also known as: Locust tree

The black locust tree often garners a negative reputation in many parts of the U.S. due to its aggressive growth habits, but it also offers several advantages. For instance, it serves as a crucial nectar source for honeybees and is effective for windbreaks due to its fast growth rate, typically between 91 to 122 cm annually. Additionally, its wood is exceptionally rot-resistant, making it valuable for use in fence posts and other outdoor applications. However, one should note that the plant is highly toxic and should not be ingested under any circumstances. Despite its benefits, the black locust requires careful management to control its invasive tendencies.

In This Article

Care Tips Water Sunlight Temperature Soil Fertilize Prune Propagation Repotting Toxicity

Attributes of Black locust

Lifespan

Perennial

Plant Type

Tree

Plant Height

10 m to 30 m

Spread

6 m to 15 m

Leaf Color

Green Blue Yellow

Flower Size

1.6 cm to 1.9 cm

Flower Color

White

Images of Black locust

Quickly Identify Black locust

Fragrant white flowers in pendant racemes up to 8 inches long, with pea-like petals in a 'standard,' 'wings,' and 'keel' arrangement.

Smooth, elongated purple-brown pods, 2 to 4 inches long, containing 4 to 8 red-brown kidney-shaped seeds.

Dark blue-green pinnate leaves with up to 23 lance-shaped to ovate leaflets, creating a feather-like appearance.

Sturdy trunk with dark brown to gray deeply furrowed bark, scaly ridges, and branches with short paired spines.

Thick stems with grayish to dark brown color, featuring stout woody texture and branching pattern with short spines.

Scientific Classification of Black locust

Phylum

Vascular plants

Class

Dicotyledons

Order

Legumes, milkworts and allies

Family

Legume

Genus

Locusts

Species

Black locust

Planting and Growing of Black locust

Care Difficulty

Easy

Watering Schedule

Every 2 days

Sunlight Requirements

Full sun

Sunshine Duration

6-10 hours

Ideal Temperature

59-68℉

Soil Type

Potting Mix, Peat Mix

Soil pH

6.5-7.5

Fertilizer Type

Balanced

Pruning Season

Spring, Summer

Pruning Area

Branches, Leaves

Pruning Frequency

2 times a year

Repotting Season

Spring

Pot Type

Plastic, Ceramic

How to Water Black locust?

Robinia pseudoacacia prefers deep watering, ensuring the soil is moist but not waterlogged. Use around 2000 mL of water per session to reach the roots effectively. It's crucial to water thoroughly to prevent surface evaporation and encourage deep root growth.

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What Are the Sunlight Requirements for Black locust?

Sunlight Requirements: Full sun, Partial sun

Duration of light: 6 to 8 hours

Robinia pseudoacacia thrives best in conditions offering full sun to partial sun, benefiting from 6-8 hours of light daily. This balance supports vigorous growth and plentiful blooms.

What is the ideal lighting condition for Robinia pseudoacacia? ›

How can one achieve the ideal lighting condition? ›

What are the benefits of providing ideal lighting conditions to this plant? ›

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What Is the Ideal Temperature Range for Black locust?

Ideal Temperature: 59 ~ 68℉

The ideal temperature range for the growth of Robinia pseudoacacia is between 59°F and 68°F. Within this temperature bracket, the plant is able to carry out photosynthesis efficiently, leading to steady growth and healthy foliage development. Temperatures within this range provide the optimal conditions for nutrient uptake and metabolism, contributing to a robust growth cycle.

What Soil is Best for Black locust?

Soil type: Sandy soil, Loam, Clay soil, Sandy loam

Soil PH: 6.5 ~ 7.5

Robinia pseudoacacia thrives in well-drained soil. Proper drainage prevents waterlogging, which could otherwise lead to root rot and poor plant health. The plant benefits from nutrient-rich soil, which provides essential minerals for robust growth and vibrant foliage. A good balance of organic matter is key in sustaining its needs. A mix between sandy and loamy textures is ideal for Robinia pseudoacacia as it offers the right balance of moisture retention and aeration, ensuring healthy root development. More About Soil→

How to Fertilize Black locust?

Fertilizer type: Balanced

When fertilizing Robinia pseudoacacia, apply a balanced all-purpose fertilizer. Use 5-10-10 or 10-10-10 NPK ratios; around 1 pound per inch of trunk diameter is suitable for mature trees. Adjust based on soil fertility. More About Fertilizing Techniques→

How to Prune Black locust?

Pruning Time: Spring, Summer, Autumn

Robinia pseudoacacia tends to grow rapidly and can become quite tall. Focus on thinning out dense areas to improve airflow and sunlight penetration. Start by removing any cross branches that rub against each other to prevent wounds that can invite disease. Shape your Robinia pseudoacacia gradually. Remove no more than a third of the tree's foliage in a single season to avoid stressing the plant. Cut branches at a slight angle, just outside the branch collar, to encourage proper healing. Regular shaping helps in maintaining desired aesthetics and structural balance. More About Pruning Techniques→

How to Propagate Black locust plant?

Propagate Time: Spring, Late spring, Early spring

Collect seeds from mature Robinia pseudoacacia pods, which should be allowed to air dry. Scarify the seeds by lightly rubbing them with sandpaper to break the hard outer coat, enhancing water absorption and improving germination rates.

Cut semi-hardwood stems of about 15-20 cm using sharp shears. Remove the lower leaves and dip the cut end in rooting hormone to promote root development. The cuttings should be planted in a mix of sand and peat moss for optimal drainage.

In early spring, cut 5-10 cm sections of root from mature plants. Place horizontally in a tray with a light covering of soil. Keep the soil moist and maintain a warm environment to ensure new growth emerges from the cuttings.

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How to Repot Black locust plant?

Repotting frequency: Every two to three years

Look for signs such as roots growing out of the drainage holes or the plant becoming root-bound. These are indicators that it's time to give your Robinia pseudoacacia a new, more spacious home. Ideally, try to repot during the active growing season for best results.

Select a pot that is slightly larger than the current one and ensures proper drainage to prevent waterlogging. Using a pot that provides enough space for root growth helps the plant stabilize as it matures, leading to healthier growth and development.

Opt for a well-drained loamy soil mixture that allows for air circulation around the roots while providing essential nutrients. This type of soil prevents root rot and encourages robust growth by maintaining ideal moisture levels.

Toxicity of Black locust

Is Black locust toxic to humans?

Every part of the black locust tree is toxic to humans upon ingestion. This is particularly concerning for children who might unknowingly consume parts of the plant. The bark, seeds, and new shoots are the most hazardous. While black locust poisoning is seldom lethal, the symptoms can linger for several days or even weeks. The level of toxicity is categorized as moderate to high, and symptoms may encompass abdominal pain, diarrhea, muscle weakness, dilated pupils, and rapid respiration.

Is Black locust toxic to cat?

The black locust displays a moderate toxicity level for cats and poses a risk of harm should any portion of the plant be consumed. This plant's entire structure is toxic, extending from its leaves to its roots, making exposure particularly hazardous. If a cat were to ingest black locust, it may show signs of physical distress, which could include gastrointestinal disturbances among various symptoms. Since early detection and intervention are vital, it is crucial to take a cat to a veterinary clinic without delay if poisoning is suspected.

Is Black locust toxic to dog?

The black locust tree poses a moderate level of toxicity to dogs. All components of the plant are deemed toxic, meaning that canines are at risk of poisoning from consuming any part of it. Should a dog ingest parts of the black locust, they might display signs such as gastrointestinal distress, lethargy, and depression. It is essential for dog owners to restrict their pets' access to black locust and to keep a close watch on them if they are in proximity to this plant. In the case that a dog consumes any portion of the black locust, it is crucial to seek prompt veterinary assistance to ensure appropriate treatment and management of the symptoms.

WARNING

The judgment on toxicity and danger is for reference only. We DO NOT GUARANTEE any accuracy of such judgment. Therefore, you SHALL NOT rely on such judgment. It is IMPORTANT TO SEEK PROFESSIONAL ADVICE in advance when necessary.

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