Growing a juniper from seed is possible, but it takes patience. Juniper seeds are deeply dormant, and most will not sprout until they have been through a warm, moist period followed by a cold one, much as they would after falling to the ground in late summer and sitting through a winter. Expect the process to take several months before you see seedlings.

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The short answer: collect ripe, blue berry-like cones in fall, remove the seeds from the pulp, then give them a moist-warm period followed by a moist-cold period. One nursery procedure for eastern redcedar uses 30 days at room temperature followed by 90 days at 33 to 35°F in moist peat. Alternatively, sow cleaned seed outdoors in late summer or fall and let nature provide the warm and cold periods. Germination is often slow and uneven.

Why juniper seeds are slow to sprout

The USDA Natural Resources Conservation Service (NRCS) describes eastern redcedar (Juniperus virginiana) seeds as consistently highly dormant, with germination often delayed. A Kansas State forestry specialist writing in a USDA Forest Service nursery proceedings paper calls the species notorious for inconsistent germination, with results that vary by seed source and crop year.

The dormancy has two parts: a hard seed coat and an embryo that needs chilling. That is why the recommended treatments combine a warm period, which helps soften the coat, with a cold period, which breaks the embryo’s dormancy.

Most published seed research covers eastern redcedar, the most widespread juniper in the eastern United States. Other junipers have similar dormancy, but timings may differ.

Step 1: Collect ripe seed in fall

According to the NRCS, eastern redcedar’s female cones are dark blue or bluish purple, waxy and berry-like, about 3/16 to 1/4 inch long, and ripen in September through October. Each cone holds one to three seeds.

Find a female tree. The NRCS notes that male and female cones are usually on separate trees, so only female trees bear the blue “berries”.
Pick only ripe cones. The NRCS advises gathering fruit in fall, September to November, as soon as the cones are ripe, and picking only ripe ones.
Expect good and bad years. Red cedars start bearing at about 10 years old and produce cones every two to three years, according to the NRCS.
Check the seed. The NRCS notes that the share of filled seeds varies widely from tree to tree, and recommends cutting a few seeds open to check that they are filled.

Step 2: Clean the seeds

The pulp around the seed is resinous. The NRCS says seeds should be removed from the fruits for the best germination. It describes recovering them by macerating, or mashing, the fruits in water and floating the seeds to the top, and notes that adding detergent to the water helps separate seeds from the resinous fruit.

If you are not sowing right away, the NRCS says redcedar seed stores well when dried to 10 to 20 percent moisture and kept in a sealed container in the cold.

Step 3: Stratify the seed

Stratification means holding seeds moist at controlled temperatures to break dormancy. Several published methods work:

Method	Warm period	Cold period	Source
Nursery procedure for container seedlings	30 days moist at room temperature (70 to 80°F), after a 24-hour soak in water	90 days moist at 33 to 35°F	Loucks, USDA Forest Service proceedings
Research best treatment	6 weeks moist at about 75°F (24°C), after a 96-hour soak in citric acid	10 weeks moist at about 41°F (5°C)	USDA Forest Service research paper RM-263
Outdoor sowing	Late summer warmth	Natural winter chilling	NRCS

The NRCS also describes a nursery treatment using sulfuric acid to soften the seed coat. That is not a home method. It notes that two to three months of warm stratification can be used instead of the acid treatment.

For a home version of the Loucks method:

Soak the cleaned seed in water for 24 hours.
Mix it with moist (not wet) peat or a similar medium in a labeled bag or container with some drainage.
Keep it at room temperature for about 30 days.
Move it to a refrigerator at just above freezing for about 90 days.
Check every couple of weeks that the medium is still moist and not moldy.

The Forest Service research found that fresh seed may need less warm stratification, and that seed from different regions responded differently. Loucks also found that seed dried for storage needed a different treatment than freshly collected seed. So if your first batch fails, try adjusting the warm period.

Step 4: Sow the seed

The NRCS says redcedar seed is usually sown in nurseries in late summer or fall, though it can be sown in spring or summer, and that fall sowing takes advantage of natural chilling. It also notes that germination is delayed at temperatures above 60°F, so stratified seed does best sown into cool conditions in early spring.

Sow seeds shallowly in a well-drained seed-starting mix or a prepared outdoor bed.
Keep the soil evenly moist but not soggy.
Protect outdoor beds from birds and rodents with fine mesh.
Be patient: some seeds may not sprout until the following year.

Step 5: Grow on the seedlings

Junipers are sun lovers. NC State Extension says eastern red cedar has the best drought resistance of any conifer native to the eastern United States, prefers moist soil but not continuously wet soil, and tolerates shade only when it is very young. Keep seedlings in pots in a bright spot for their first season, then plant them out once they are large enough to handle. See how to plant juniper trees for planting depth and spacing, and whether junipers will grow in shade before choosing a site.

Seed or cuttings?

Seed is the natural way to grow a species such as eastern redcedar, and it is how nurseries raise rootstock. The NRCS notes that redcedar is generally propagated by cuttings and that redcedar seedlings are commonly used as rootstock for grafting ornamental juniper cultivars. If you want a plant identical to a named variety, such as a specific columnar or blue juniper, a cutting from that plant is a better route than seed.

Not sure which juniper you have? See how to identify a juniper tree and how tall juniper trees get.

Key takeaways

Collect ripe blue cones from female trees in fall and clean the seed.
Juniper seed is deeply dormant and usually needs a warm period followed by a cold period.
A 30-day warm, 90-day cold moist stratification is a proven nursery method for eastern redcedar.
Fall sowing outdoors is the low-effort alternative.
Expect slow, uneven germination, and use cuttings if you want a copy of a named variety.

Sources

Eastern Red Cedar Plant Guide, USDA Natural Resources Conservation Service
Effects of Treatment and Seed Source on Germination of Eastern Redcedar Seed (RM-RP-263), USDA Forest Service
Pregermination Treatment of Eastern Redcedar Seed (Loucks 1995, PNW-GTR-365), USDA Forest Service, Reforestation, Nurseries and Genetics Resources
Juniperus virginiana (Eastern Red Cedar), NC State Extension Gardener Plant Toolbox

Top photo: Ayotte, Gilles, 1948-, CC BY-SA 4.0, via Wikimedia Commons

How to Grow a Juniper Tree from Seed