One of the common names for this needled evergreen is a clear identifier: It is often known as the umbrella pine. Beginning life as a rounded shrub-like tree, the stone pine (Pinus pinea) gradually matures into a towering tree with a characteristic mushroom-shaped canopy. The shape is instantly recognizable to anyone who has traveled in Mediterranean regions, where it is native. It is also commonly grown in the coastal regions of southern California. The shape of the stone pine is quite different from the pyramidal shape common to most evergreen trees.
Stone pine belongs to the Pinaceae family, which includes all pine trees as well as other deciduous conifers (Larix spp.), spruce trees, fir trees, Douglas firs (Pseudotsuga spp.), cedars (Cedrus spp.) and hemlocks (Tsuga spp.) With the stone pine, each fascicle (bundle) contains two pine needles that are 2 to 4 inches long. The new growth that is formed each spring at the tip of each branch is called a conifer candle.
The stone pine tree is the prime source for edible pine nuts in Europe—though they are not actual nuts, but rather the seeds contained within the cones. Oddly, eating the seeds can cause a phenomenon called pine nut mouth, producing a bad taste in your mouth for days. However, this does go away, and scientists have been unable to find any medically significant side effects for humans.
These trees grow rather slowly in the early years, achieving a height of about 15 feet over the first five years. But if you expect to grow it to maturity, be aware that stone pine is a large tree best suited for an expansive property, where it can serve as a specimen tree or can planted in groups to produce a shaded glade or screen.
Stone pine is sometimes sold as a small living Christmas tree for indoor use. In appropriate climates, the potted tree can then be transplanted into the outdoor landscape.
|Botanical Name||Pinus pinea|
|Common Name||Stone pine, umbrella pine, Italian stone pine, parasol pine|
|Plant Type||Needled evergreen|
|Mature Size||40 to 60 feet; 20- to 40-foot spread|
|Sun Exposure||Full sun|
|Soil Type||Dry to medium-moisture, well-drained soil|
|Soil pH||Tolerates a wide range, acidic to slightly alkaline|
|Hardiness Zones||8 to 10 (USDA)|
|Native Area||Mediterranean region|
How to Grow Stone Pine Trees
Stone pine trees are quite durable once established, but they can be temperamental in the early years and are hard to restore if problems arise. This tree is best planted in a dry to medium-moisture soil in a full-sun location, with plenty of space for growth. They have a natural preference for soils that are slightly sandy.
You can use fallen pine needles as a natural mulch to help water retention and keep weeds at bay. Make sure to leave a space of a few inches between the trunk and the mulch. If they touch, this can cause problems like fungal diseases and make it harder for the tree to get oxygen.
Stone pines often assume a shrubby, multi-stemmed shape when young, but as they grow upward, the multiple trunks usually merge into a single trunk, which then diverges into spreading branches high above the ground. Lower branches will naturally fall away as the tree grows upward and begin to assume its umbrella shape. No additional trimming is generally needed.
If you are growing this tree for the pine nuts, be aware that it may take many years before cones are produced and then an additional three years or so before they produce mature, edible seeds.
Plant a stone pine tree in a full-sun location.
Stone pine prefers a well-drained soil that is not too moist. It tolerates a wide range of soil pH, though like most pines, it thrives under slightly acid soil conditions.
This is a drought tolerant tree once established, but in the first growing seasons make sure to give it adequate watering to help root establishment. This species is native to dry Mediterranean regions, so the best environment will mimic those conditions.
Temperature and Humidity
As a native of the Mediterranean, stone pine prefers a mildly warm environment without notable temperature swings, and relatively dry conditions. It does not do well in very humid environments, where it can be susceptible to fungal problems and rot. Nor does it like environments where there is a vast difference between winter and summer temperatures. These trees are easily damaged by ice.
Once established, stone pine trees need no feeding. In the first year or two, application of an acid fertilizer may help if the tree is not developing properly.
Pruning Stone Pine Trees
There should be little pruning needed unless you need to take care of branches that are dead, diseased, or damaged. As the tree grows upward, the lower branches tend to shed, gradually transforming the plant from a rounded shrubby form into a towering shade tree. Some gardeners prefer to shape the umbrella-shaped canopy by targeted pruning.
Propagating Stone Pine
The most common method of propagation is from seed, but seeds will not be viable unless the tree is relatively mature. The tree must be several years into cone production before the seeds can be propagated. Seed propagation is a somewhat involved process:
Collect seeds from a dried cone, then soak them in water overnight. Then, place the seeds in a plastic bag filled with damp sphagnum moss and place in a refrigerator for 60 to 90 days of chilling to trigger germination.
Fill some small pots with seed-starter mix (or a mixture of sand, peat moss, and vermiculite), and plant the seeds about 1/4 inch deep. Spray the surface with water and place the pots in a sunny window. Check daily and keep the soil surface moist with spraying. As the seeds sprout, thin out the weaker seedlings.
Grow the plants in their pots for a full year until branches begin to form. They are then ready for transplanting into a garden location.
Harvesting Stone Pine Nuts
You can harvest pine nuts from your trees by collecting cones and placing them in a warm sunny location until they fully open. The seeds may fall out on their own, but it is more likely that you will need to break the cone apart to release the seeds. The edible portions of the seeds are contained within shells that you will have to remove.
Common Pests and Diseases
There are few serious disease problems found with this species. You may see episodes of pine needle cast—a fungal disease that causes the needles to turn brownish-red and fall off. This is usually a symptom of other problems such as bark beetles, so check the tree for other pests and diseases.
Possible pests include bark beetles and Western conifer seed bug (Leptoglossus occidentalis). Wester conifer seed bugs rarely harm the tree permanently, though they will reduce seed production. Bark beetles are a more serious problem, though not common on stone pines. These pests cut tunnels in the inner bark layer, beneath the outer bark. They are hard to treat with pesticides, so the recommended control is to remove and destroy affected branches. A major infestation may require the removal of the entire tree.