Malva olbia aka Garden Tree Mallow

Malva olbia is an easy-care plant that thrives with minimal attention once established. It's drought-tolerant, pest-resistant, and doesn't require regular feeding or watering after the first growing season. The main consideration is providing enough space for its vigorous growth. Note that plants are typically short-lived, lasting around 5 years, but propagate easily from cuttings.

Malva olbia is a vigorous, fast-growing shrub that can reach 1.5-2.5 metres in both height and spread. The semi-evergreen shrub has a bushy, upright habit with 3-5 lobed, densely downy grey-green leaves. Space plants 80cm to 1 metre apart to accommodate their mature size.

Malva olbia is native to the Western and Central Mediterranean region. Its natural range includes Algeria, the Balearic Islands, Corsica, France, Italy, Libya, Morocco, Portugal, Sardinia, Sicily, Spain, and Tunisia. It grows naturally in the subtropical biome and has been introduced to California where it has naturalized.

Malva olbia is hardy through most of the UK with an RHS rating of H4, tolerating winter temperatures down to -10°C (14°F). Very hardy varieties can withstand temperatures as low as -15°C (5°F). In USDA zones 6-9, it grows reliably outdoors year-round. Provide a sheltered position protected from cold, drying winds, especially in frost-prone areas.

Malva olbia requires minimal to no fertilizing once established in the ground. In fact, soil that is too rich will produce abundant foliage at the expense of flowers. For container-grown plants, apply a flower fertilizer throughout the growing season. A light application of organic matter or compost as mulch after spring pruning provides sufficient nutrients for garden plants.

Malva olbia produces deep pink flowers with slightly notched petals and darker veins continuously from June through September. The hollyhock-like blooms can reach up to 7-8cm (3 inches) across and smother the branches throughout summer. Deadheading spent flowers encourages continued blooming. The flowers are excellent for cutting and highly attractive to pollinators including bees and butterflies.

Prune Malva olbia hard in early spring, cutting back to 30cm (12 inches) from ground level after the risk of severe frost has passed. This encourages dense, vigorous growth and prevents the plant becoming leggy. In autumn, shorten branches by half in exposed areas to minimize wind damage during winter. Critically, avoid fall pruning to the base as this can cause stump rot. Apply a generous mulch of compost after spring pruning.

Malva olbia propagates easily from softwood cuttings taken in early summer (April-June). Take 10-15cm (4-6 inch) cuttings from healthy stem tips or basal shoots, remove lower leaves, and root in well-draining compost. Seeds can also be sown in spring, though seedlings may not replicate named cultivar characteristics. Regular propagation is recommended as plants are typically short-lived (around 5 years).

Several notable cultivars exist, many of which are hybrids with Malva thuringiaca (designated Malva × clementii). 'Rosea' is the classic variety with deep pink flowers and has received the RHS Award of Garden Merit. 'Barnsley' features white flowers aging to shell pink. Other cultivars include 'Red Rum' (also AGM), 'Lilac Lady', 'Eye Catcher', 'Pink Frills', and 'Wembdon Variegated'. These hybrids often have rounder, more colorful flowers than the species.

Malva olbia grows successfully outdoors year-round in USDA zones 6-9 and RHS hardiness zone H4 regions. It's hardy through most of the UK and similar climates. Choose a sheltered, sunny position protected from cold, drying winds. In marginal areas, provide winter protection during severe cold spells. The plant is borderline hardy in colder regions and may need moving to a sheltered spot or container in zones 5 and below.

Malva olbia is relatively pest-resistant but can be affected by aphids. The main disease concerns are fungal: rust (appearing as brown blisters on leaf undersides), stem rot, and soil-borne fungal diseases. Remove affected foliage promptly when disease appears. Avoid fall hard pruning which can cause stump rot. The plant is deer and rabbit resistant, and its flowers attract beneficial butterflies while the foliage hosts butterfly larvae.

Malva olbia is pollinated by insects, particularly bees and butterflies. The Royal Horticultural Society considers it an excellent plant for attracting pollinators. The open, nectar-rich pink flowers attract honeybees, bumblebees (including Bombus lapidarius and B. pascuorum), solitary bees, and various hoverfly species. Butterflies including the Painted Lady are also drawn to the blooms, making it valuable for wildlife gardens.

In spring, prune hard to 30cm after frost risk passes, then apply compost mulch. Through summer, water during dry spells if newly planted; established plants are drought-tolerant. Deadhead regularly to prolong flowering. In autumn, reduce tall growth by half in exposed areas to prevent wind damage, but avoid hard pruning. In winter, provide protection in severe cold and ensure good drainage to prevent root rot.