Strawberry Tree (Arbutus unedo)

Killarney Strawberry Tree, Strawberry Tree, Strawberry Madrone

Arbutus unedo is an evergreen shrub or a small tree native to Europe. It is colloquially called a strawberry tree because its bright red fruits somewhat resemble strawberries. The fruits of this lovely plant are very nutritious and full of sugar, which is why they are mostly used for making jams, pastries, fruit yogurts, and alcoholic beverages.

I. Appearance and Characteristics 

Arbutus unedo, commonly known as strawberry tree, or chorleywood in the United Kingdom, is an evergreen shrub or small tree in the family Ericaceae, native to the Mediterranean Basin and Western Europe. The tree is well known for its fruits, the arbutus berry, which bear some resemblance to the strawberry, hence the common name strawberry tree. However, it is not closely related to true strawberries of the genus Fragaria.

Its presence in Ireland also lends it the name “Irish strawberry tree”, or cain, or cane apple (from the Irish name for the tree, caithne), or sometimes “Killarney strawberry tree”. The strawberry tree is the national tree of Italy because of its green leaves, its white flowers and its red berries, colors that recall the Italian flag.

Arbutus unedo was one of the many species described by Carl Linnaeus in Volume One of his landmark 1753 work Species Plantarum, giving it the name it still bears today.

A study published in 2001 which analyzed ribosomal DNA from Arbutus and related genera found Arbutus to be paraphyletic, and A. unedo to be closely related to the other Mediterranean Basin species such as A. andrachne and A. canariensis and not to the western North American members of the genus.

Arbutus unedo grows to 4–7 m (13–23 ft) tall, rarely up to 15 m (50 ft), with a trunk diameter of up to 80 cm (31 in). It grows in hardiness zones 7–10.

The leaves are green and glossy on the upper side, dull on the underside, 8–10 cm (3–4 in) long and 3–4 cm (1–1+1⁄2 in) broad, laurel-like and with a serrated or serrated margin.

The hermaphrodite flowers are white (yellow when desiccated), bell-shaped, 7–8 mm (1⁄4–5⁄16 in) in diameter, and flower from a reddish hanging panicle in autumn. They are pollinated by bees, and have a mild sweet scent.

Twigs are reddish-brown and abundantly foliage, and often have small hairs.

The fruit is a red berry, 7–20 mm (1⁄4–13⁄16 in) diameter, spherical in shape with a rough surface. It matures in about 12 months, in autumn, at the same time as the next flowering. It is edible; the fruit is sweet when reddish. Seeds are small, brown and angular and are often dispersed by frugivorous birds.

The name unedo is attributed to Pliny the Elder, who allegedly claimed that “unum tantum edo”, meaning “I eat only one”. It is not known whether he meant that the fruit was so good he could eat only one, or whether he meant that the fruit was uninteresting so he ate only one.

Arbutus unedo is quite an easy plant to cultivate, and is adaptable to many climates. Once established it is fairly drought resistant, frost resistant, shade tolerant and salt tolerant.

Lower production of fruit mass has however been reported in case of summer droughts, and frosts in flowering time were seen to decrease the numbers of fruits.

Arbutus unedo is naturally adapted to dry summer climates, and has become a very popular ornamental plant in California and the rest of the west coast of North America. It can grow easily in USDA hardiness zone 7 or warmer.

It also grows well in the cool, wet summers of western Ireland and England, and temperate regions of Europe and Asia. Pests include scales and thrips, and diseases include anthracnose, Phytophthora, root rot, and rust.

II. How to Grow and Care

Sunlight

Light plays an indispensable role in the life of a strawberry tree. Just like us humans who thrive in sunlight, most strawberry tree varieties need full sun to maximize their growth potential.

Ensure your chosen planting location receives at least six to eight hours of direct sunlight daily for optimal growth. The increased light encourages flower bloom, which in turn, leads to bountiful fruit production.

In addition to direct sunlight, it is important to consider the intensity and duration of light. Strawberry trees benefit from bright, consistent light throughout the day. Avoid areas with excessive shade or areas that are prone to long periods of darkness.

Temperature and Humidity

Strawberry trees are hardy in zones 7 and above and most humidity levels. However, the tree will not thrive in excessively humid areas.

Watering

The Strawberry tree should be watered regularly when it is first planted until roots are solidly established. If planted outdoors, this species does not require regular watering in the winter season, but it should be given deep root watering regularly during the dry summer months. Soil should remain slightly moist between waterings.

Soil

Like other ericaceous plants, this tree does best in acidic soil. It can also tolerate a neutral pH. You can make your soil more acidic as needed.

Fertilizing

The strawberry tree should be fertilized with an organic fertilizer like manure. A mineral fertilizer is also acceptable for this species. Fertilization should occur every few weeks in the fall, spring, and summer months. Fertilization is not necessary during the winter.

Planting Instructions

Pruning

Pruning is not usually necessary for this tree unless branches are growing the wrong way or there are dead, diseased, or dying branches. If you do wish to prune, do so at the end of winter and into early spring. You can also train the shrub so that it has more of a tree form with a single trunk.

Propagation

For air layering, you will need a sharp knife, rooting hormone (optional), a growing medium like sphagnum moss, plastic wrap, zip ties (or wire, electrical tape, or string), a pot, and slightly acidic, well-draining soil.

  • In early to late spring, pick a branch that would make a good tree specimen, 1 to 2 years old, and clear a 1-foot section of any leaves.
  • Cut a ring around the branch, and 1 inch below, another ring; connect the two rings with a vertical cut, and remove the bark and the soft tissue of the cambium layer, leaving the woody center.
  • Apply rooting hormone, if using, around the top cut.
  • Apply moist (but not wet) sphagnum moss around the wound, and wrap it with plastic wrap so that it’s sealed tightly; the packed moss should be 3 to 4 inches thick.
  • Secure the plastic wrap on each end (you can use zip ties, wire, electrical tape, or string)
  • Check for moisture, and if the moss is dry, spritz to moisten. 
  • Roots should appear in 8 to 12 weeks; once roots appear, cut the stem just below the rooted area.
  • Remove the plastic wrap—but leave the moss so the roots are not disturbed—and plant the branch in a pot filled with slightly acidic, well-draining potting soil. Place in a spot with bright, indirect light and keep the soil evenly moist until the roots are well established.

Propagation by Cuttings

The best time to take cuttings from a strawberry tree is in July. You will need a sterilized garden cutting tool, rooting hormone, soilless potting mix, and 6-inch pots with a drainage hole.

  • Choose new growth—green, soft (non-woody) stems—for cuttings.
  • Using a sterilized cutting tool, make a clean cut just below a node; each cutting should be 4 to 6 inches long and contain at least two leaves and one node.
  • Remove all but one or two leaves on each cutting and apply rooting hormone to the cut’s end.
  • In each pot filled with potting mix, make a hole with a pencil, or something similar, and gently place the cutting in the hole. Tamp soil around the cutting and water the potted cutting.
  • Cover pots with a plastic bag, which provides a warm, humid environment. Don’t seal completely so there’s some airflow.
  • Keep the cuttings in a warm spot with bright light until they are hardy enough for outdoor planting.

Overwintering

Younger trees may need protective burlap covers in cold weather and frosts to prevent damage to flowers and fruits. Covers can also protect the younger trees from cold winds.

Pests and Diseases

Common Pests 

One common pest that can wreak havoc on strawberry trees is birds. These feathered creatures, with their keen eyes and nimble beaks, are quick to snatch up the tree’s delicious fruits. As you admire the beauty of your strawberry tree, keep a watchful eye for any signs of bird activity. Consider using bird netting or other protective measures to prevent these winged thieves from enjoying the fruits before you do.

Another pest that can cause damage to strawberry trees is slugs. These slimy creatures are particularly fond of the tree’s juicy fruits and tender leaves. To keep your strawberry tree safe from slugs, regularly inspect the foliage and surrounding areas for any signs of their presence. If you spot any slugs, you can use slug traps or other organic methods to control their population and protect your tree.

In addition to birds and slugs, rodents can also pose a threat to your strawberry tree. Squirrels, mice, and other small mammals are known to enjoy the tree’s fruits just as much as we do. These clever creatures can quickly find their way to the tree, leaving you with fewer fruits to enjoy. To deter rodents from feasting on your strawberry tree, consider using barriers or repellents that are safe for both the tree and the environment.

Common Diseases 

While pests can be a nuisance, diseases can also affect the health of strawberry trees. One common disease is root rot, which is caused by excessive moisture in the soil. When the soil becomes waterlogged, it creates the perfect environment for fungi to thrive, leading to root rot. To prevent this disease, ensure that your strawberry tree is planted in well-draining soil and avoid over-watering. Regularly check the soil moisture levels and adjust your watering schedule accordingly.

Another disease that can affect strawberry trees is Phytophthora. This fungal pathogen can cause root and crown rot, leading to stunted growth and wilting foliage. Phytophthora thrives in poorly drained soil and can spread quickly if left unchecked.

To protect your strawberry tree from this disease, it is crucial to maintain proper drainage and avoid waterlogged conditions. Additionally, practicing good garden hygiene by removing any infected plant material can help prevent the spread of Phytophthora.

Caring for a strawberry tree is not only about tending to its needs but also about fostering a deeper connection with nature. As you embark on your journey to nurture and grow these beautiful trees, you become a part of the circle of life in your garden. The sweet rewards of your efforts will not only fill your heart but also your garden with the abundance of strawberry trees.

III. Uses and Benefits 

Culinary uses

Arbutus berries have a high content of sugars (40%), and antioxidant vitamins such as vitamin C, beta-carotene, niacin, tocopherols, and organic acids that are precursors to omega-3 and omega-6 fatty acids (nearly 9%). They are edible fresh, but that is an uncommon consumption, especially because the mature fruit tends to bruise very easily, making transportation difficult.

They are used mostly for jam, marmalades, yogurt and alcoholic beverages, such as the Portuguese medronho, a type of strong brandy. Many regions of Albania prepare the traditional drink rakia from the fruits of the plant (mare or kocimare in Albanian), whence comes the name of the drink, which is raki kocimare.

The flowers are pollinated by bees, and the resulting honey is bitter tasting but still considered a delicacy.

Medicinal uses

Arbutus unedo’s leaves have been employed in traditional and folk medicine in the form of a decoction said to have the following properties: astringent, diuretic, urinary anti-septic, antiseptic, intoxicant, rheumatism, tonic, and more recently, in the therapy of hypertension and diabetes.

The leaves are reported to have a high concentration of flavonol antioxidants, especially quercetin, best extracted with a decoction, and together with the fruits are a source of antioxidants.

The leaves also have anti-inflammatory properties

The nectar contains the isoprenoid unedone (2-(1,2-dihydroxypropyl)-4,4,8-trimethyl-1-oxaspiro[2.5]oct-7-en-6-one) which is biologically active against a common and debilitating parasite of bumble bees, Crithidia bombi, so could provide a naturally occurring way for bees to withstand the burden of disease which has been reported to be a contributing factor in pollinator declines. The compound is glycosylated to an inactive form unedone-8-O-glycoside once consumed by the bee (perhaps to reduce any toxic effects against the bee herself) then transformed back to the active aglycone by the bee’s microbiome in the hindgut where the parasite is most prevalent and damaging – suggesting that the microbiome assists in the anti-parasitic process.

Ecological design

In landscape design, ecosystem restoration or permaculture based designs, A. unedo can have many purposes. While the ornamental one is the most common, this can be a valuable plant also for restoring degraded ecosystems and preventing desertification. Being a pioneer plant and growing well also in poor soils, it can be used in a wide array of situations.

  • The flowers are a significant source of nectar and pollen for bees, while the fruits are food for the birds.
  • Its salt tolerance, coupled with it being an evergreen, make it a good choice for wind barriers in lands close to the sea.
  • A. unedo is fire resistant (can regrow after a fire), and being a pioneer plant can contribute to the discontinuity of fire-prone pines and eucalyptus monocultures; for the same reasons it is a good candidate for reforestation in Mediterranean areas.
  • The dense foliage throughout the year can be a shelter for insects and small animals during the winter.
  • Its extensive root system can help in the soil stabilization process.

Other uses

  • The wood is quite hard and well suited for various uses such as fire wood and to make pipes. Since it does not usually grow straight, it is not well suited for construction or similar uses.
  • The tree is also grown as an ornamental plant, because of its nice-looking and -smelling flowers and fruit and their interesting presence on the plant at the same time, and because it is an evergreen. It is used as a single or multi-trunked ornamental tree, and as a specimen or hedge shrub in gardens and public landscapes.

IV. Harvesting and Storage

In the late fall or early winter, usually in November or December, the strawberries on a strawberry tree are ready for picking. The berries should be picked when their skins are intensely red and slightly soft to the touch.

Strawberry Tree (Arbutus unedo) Details

Common name Killarney Strawberry Tree, Strawberry Tree, Strawberry Madrone
Botanical name Arbutus unedo
Plant type Edible
Hardiness zone 7a, 7b, 8a, 8b, 9a, 9b, 10a, 10b
Growth rate Slow
Harvest time Fall
Height 10 ft. 0 in. - 35 ft. 0 in.
Width 10 ft. 0 in. - 35 ft. 0 in.
Sunlight Full sun (6 or more hours of direct sunlight a day)
Soil condition Clay
Flower color Pink
Leaf color Green