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.
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 be planted in groups to produce a shaded glade or screen.
|Common Name||Stone pine, umbrella pine, Italian stone pine, parasol pine|
|Botanical Name||Pinus pinea|
|Mature Size||40-60 ft. tall, 20-40 ft. wide|
|Soil pH||Acidic, alkaline|
|Hardiness Zones||8-10 (USDA)|
Stone Pine Care
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 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 with 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.
Plant a stone pine tree in a full-sun location.
Stone pine prefers well-drained soil that is not too moist. It tolerates a wide range of soil pH levels, though, like most pines, it thrives under slightly acidic 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, the application of an acid fertilizer may help if the tree is not developing properly.
The stone pine most commonly available is the straight species. It is the primary source for edible pine nuts in Europe. There are 20 species of pine trees that also produce seeds for harvesting, including:
- Colorado pinion (P. edulis), a pine native to North America that can get up to 45 ft. tall with a short trunk
- Mexican pinon (P. cembroides), a compact tree also native to North America, growing 20 to 30 ft. tall
- Korean pine, also known as Chinese nut pine (P. koraiensis), a hardy pine with pyramidal shape, growing 30 to 40 ft. tall
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 shrub into a towering shade tree. Some gardeners prefer to mold the umbrella-shaped canopy by targeted pruning.
Propagating Stone Pine
While starting stone pine from seeds is the method most commonly used to propagate the tree, it is also possible to propagate from cuttings. Here's how:
- Using sharp shears, cut a piece of new growth (softwood) that's about six inches in length. The best time to take a cutting is in the late spring or early summer.
- Use your shears to remove any branches or needles from the bottom of the cutting. You will not want any needles touching the soil.
- Use a small knife to make grooves along the length of the cutting.
- Dip the grooved end into rooting hormone and place it in a pot filled with potting soil.
- Keep the soil moist but don't overwater.
- After a few months tug gently on the new plants to check for root development. Once roots have sprouted, it is OK to transplant the tree into the ground. It can also live in a pot for a few years, as long as the container is deep enough.
How to Grow Stone Pine From Seed
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.
It begins with harvesting the seeds, which can be done 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.
After collecting the seeds, soak them in water overnight. Then, place the seeds in a plastic bag filled with damp sphagnum moss and place them in a refrigerator for 60-90 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.
Potting and Repotting Stone Pine
Thanks to their slow rate of growth, stone pine trees can be grown in containers for many years indoors. A terra cotta container is best because it lets excess moisture evaporate, and it is heavy enough so the tree won't topple over.
A potting mix of two parts compost (redwood compost can work well) along with one part pumice or perlite should work well as the growing medium for your tree indoors.
You'll want to keep the soil moist but not too wet. A good guide is that if the top 2 or 3 inches of the soil is dry, it is probably time to give it a drink.
Keep your potted pine in an area where it gets bright light, but avoid strong midday sun. Also, keep it away from heat sources such as a fireplace or radiator, or air vents.
Stone pine roots tend to grow at a rapid rate, even though the tree itself grows slowly, so you may want to shake the tree out of its container every six months to see if it has become rootbound. If so, it's time to repot.
Stone pine trees won't do well in cold winters so the best advice is not to plant one if you live in a cold-prone area. However, if you live in an area with big seasonal temperature swings and are growing your stone pines in pots, you can keep them outdoors from late spring to early fall and bring them back inside well before nighttime temperatures get chilly. Before bringing them back inside, you can give them a good soaking and then use ice cubes to keep them moist during the colder months.
Common Pests and Plant 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. Such an issue can be treated with a fungicide containing neem oil or copper salts.
Sometimes though, the issue could be caused by bark beetles. 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.
Other possible pests include Western conifer seed bugs (Leptoglossus occidentalis) which rarely harm the tree permanently, though they will reduce seed production.
Common Problems With Stone Pine
If you notice your pine needles turning brown but have ruled out a fungus or beetle issue, then the cause is likely root rot due to overwatering or poor soil drainage. If the tree is young, you may be able to trim away the damaged roots, correct the drainage issue and still have a successfully growing tree.
How long do stone pine trees live?
These trees live between 50 and 150 years.
How long does it take for the tree to produce pine nuts?
The pine nuts that are harvested from the tree are not actual nuts, but rather the seeds contained within the cones. It may take many years before cones are produced and then an additional three years or so before they produce mature edible seeds.
Can stone pines handle strong winds?
Not typically. If you live in an area that experiences high winds regularly, this tree is best avoided, as its somewhat delicate branches will easily snap off during big gusts.