How to Grow and Care for Alligator Juniper

Native to Mexico and the southern United States, the alligator juniper (Juniperus deppeana) is a species of juniper characterized by its unique cracked bark resembling alligator skin. The deep green to blue-green leaves of the alligator juniper are arranged in opposite decussate pairs.

As one of the largest species of juniper trees, alligator junipers planted or seeded in the spring or fall can grow to 60 feet tall in their ideal environment, but they are very slow growers so it will take them an extremely long time to reach a mature height.

Alligator Juniper Care

In their native environment, alligator junipers grow on open, rocky hills and slopes that receive full sun for the majority of the day. They are considered to be generally heat and cold-tolerant trees and are known for being adaptable to a range of growing conditions. Alligator junipers are not self-fertile and male and female trees must be planted nearby for flowering to occur. 

Alligator junipers are fairly self-sustaining and do not require too much attention. However, keep an eye out for browning leaves and tips as alligator junipers are susceptible to a host of common pests and diseases. Pruning is unnecessary.

Light

True to its native habitat, the alligator juniper is a sun-loving tree that requires full sun to thrive. Alligator junipers cannot grow in the shade, and growth may be stunted in areas that only receive partial sun.

Soil

Alligator junipers thrive in sandy, well-draining soil that is slightly acidic with a pH between 5.5 and 7.0. However, they are adaptable to a wide variety of soil conditions, as long as the medium is well-draining. 

Water

Alligator junipers are considered to be very drought-tolerant trees with low water needs. An established alligator juniper should not need supplemental watering, however, seedlings and young trees may require watering during dry periods. It is important to note that alligator junipers are susceptible to overwatering. Ensuring that the tree is planted in well-draining soil is an important step to preventing this. 

Temperature and Humidity

Alligator junipers are not an overly cold-tolerant species of juniper and can only tolerate freezing temperatures for a short period. At their extreme, alligator junipers can tolerate temperatures as low as 17 degrees Fahrenheit when they are fully dormant.

Fertilizer

As with most juniper trees, alligator junipers do not require heavy feeding. However, once established they can benefit from annual feeding with a slow-release shrub and tree fertilizer. Alternatively, alligator junipers also respond well to organic fertilizers and soil amendments. Feed alligator junipers in the late winter or early spring as the tree is coming out of dormancy to help kickstart their growing season.

Types of Alligator Juniper

There are five varieties of alligator junipers. They are considered rare due to their slow growth rate and some types are considered endangered.

• Juniperus deppeana var. Deppeana: This is the most common type of alligator juniper with the recognizable bark.
• Juniperus deppeana var. pachyphlaea: Also known as sweet-fruited juniper, is an aromatic evergreen shrub with small round fruit.
• Juniperus deppeana var. robusta: This is an endangered juniper tree that is used for firewood and lumber.
• Juniperus deppeana var. chinesis: Known as Chinese juniper, this is a favorite tree used for bonsai.
• Juniperus deppeana var. sperryi: Commonly called Sperry's juniper, this is a critically endangered type of alligator juniper.
• Juniperus deppeana var. zacatecensis: This is another endangered alligator juniper type due to deforestation.

How to Grow Alligator Juniper From Seed

While alligator junipers can be propagated in other ways, they are most easily grown from seed. Alligator juniper seeds can be sown directly into the garden in the fall, or cold-stratified over the winter and sown in the spring once the last frost has passed. Germination rates are notoriously poor for alligator juniper seeds so it's important to sow a large number of seeds at one time to ensure some success.

Alligator juniper seeds can be purchased online or in-store, or they can be collected directly from a mature tree in the late summer or early fall once the seeds have ripened. If you are not sowing the seeds outdoors immediately, the seeds should be thoroughly air-dried and cleaned to ensure that mold does not grow. Then, the seeds should be cold-stratified for 30 to 120 days at 20 to 40 degrees Fahrenheit. 

Common Pests and Plant Diseases

Unfortunately, alligator junipers are susceptible to a host of common pests and diseases.

Common pests of the alligator juniper include bagworm, spruce spider mites, and juniper scale. Insecticides are an effective way to control serious infestations of any of these common pests but the best form of control is prevention. Make a habit of checking your alligator juniper frequently for pests so that any infestations can be caught and managed early.

Common juniper diseases include twig and tip blight, as well as cedar rust. Fungicides can help proactively protect alligator junipers against such diseases, but they should be applied before an infection is present. Prompt pruning of any dead or diseased branches should keep these common diseases under control. 

Common Problems With Alligator Juniper

If you are lucky enough to have an alligator juniper growing on your property, take care to watch for any problems this stunning tree may develop. It needs minimal care, but since it's rare, it pays to check in for some maintenance.

Spindly Growth

This tree rarely if ever needs pruning but if it's becoming spindly or misshapen, consider pruning top buds to promote lateral growth. Trim dead growth of internal branches to promote air and light circulation for better results. The tree may also be hindered in its growth by too much surrounding shade which may need to be amended.

Bark Fissuring

The tree may need more protection from extreme temperature changes in the cooler months. Mulch for root protection or whitewash the lower tree trunk with water-based white paint to protect against temperature swings that tend to split bark.

Browning Leaves and Tips

Brown leaves and tips commonly mean that a fungal disease has taken hold of your juniper. Typically this can happen in warm, wet weather or if the tree is located in a boggy area that is not well-draining. Remove brown branches, leaves, and tips. Pests may also be the cause of the problem. The issue will need to be managed with insecticide.