How to Grow and Care for Stone Pine (Umbrella Pine)

The stone pine tree, also commonly called the Italian stone pine or umbrella pine, is a needled evergreen that begins life as a rounded shrub-like tree and slowly matures into a towering tree with a characteristic mushroom-shaped canopy. The shape is instantly recognizable to anyone who has traveled in its native Mediterranean regions. Stone pine trees won't do well in cold winters. The trees require full sun and well-drained soil of any pH level.

Stone Pine Care

There are a few important tips to keep in mind when caring for stone pine trees.

• Plant stone pine in slightly sandy dry to medium-moisture soil.
• Locate the tree in full sun.
• Give the tree plenty of space for growth.
• Use fallen pine needles as a natural mulch to help with water retention and keep weeds at bay.

Light

Plant a stone pine tree in a full-sun location.

Soil

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 in slightly acidic soil conditions.

Water

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.

Fertilizer

Once established, stone pine trees do not need to be fed. In the first year or two, the application of an acid fertilizer may help if the tree is not developing properly.

Types of Stone Pine

The stone pine most commonly available is the straight species. Stone pine is the primary source of edible pine nuts in Europe. Twenty species of pine trees produce seeds for consumption, including these three:

• Colorado pinyon (P. edulis): A pine native to North America that can get up to 45 feet tall with a short trunk
• Mexican pinyon (P. cembroides): A compact tree also native to North America, growing 20 to 30 feet tall
• Korean pine, Chinese nut pine (P. koraiensis): A hardy pine with a pyramidal shape, growing 30 to 40 feet tall

Pruning

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 begins to assume its umbrella shape. No additional trimming is generally 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 with 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:

1. Using sharp shears, cut a piece of new growth (softwood) that's about 6 inches in length. The best time to take a cutting is in the late spring or early summer.
2. Use disinfected shears to remove any branches or needles from the bottom of the cutting. You will not want any needles touching the soil.
3. Use a small knife to make grooves along the length of the cutting.
4. Dip the grooved end into rooting hormone and place it in a pot filled with potting soil.
5. Keep the soil moist but don't overwater.
6. 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, per these steps:

1. Harvest the seeds, which can be done by collecting cones and placing them in a warm sunny location until they are 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.
2. Soak seeds in water overnight.
3. Place soaked seeds in a plastic bag filled with damp sphagnum moss and place them in a refrigerator for 60 to 90 days of chilling to trigger germination.
4. 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.
5. Spray the surface with water and place the pots in a sunny window. Check daily and keep the soil surface moist with spraying.
6. As the seeds sprout, thin out the weaker seedlings.
7. 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 works well) along with one part pumice or perlite should work well as the growing medium for your tree indoors. Keep the soil moist but not too wet. A good guide is that when the top 2 or 3 inches of the soil is dry, it is time to give it a drink. Keep your potted pine in an area where it gets bright light, but avoid the strong midday sun. Also, keep it away from heat sources such as a fireplace, 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.

Overwintering

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.

When mulching stone pines outdoors, 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.

Common Pests & Plant Diseases

Few serious disease problems are 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

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. Watch for these issues if you plant a stone pine.

Needles Browning

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.

Snapping Branches

This tree cannot typically handle high winds. 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. These trees are also easily damaged by ice.

From: thespruce