Highlights from the June garden

It is hard to think of a better early flowering shrub than Cistus (Sun roses) with their succession of flat saucer blooms with thin tissue paper-like petals which unfurl daily over several weeks. One of the showiest is Cistus x purpureus this compact evergreen shrub has large rich pink flowers with a maroon blotch at the base of each petal and golden stamens at the centre of the blooms. Another top variety is Cistus x hybridus (syn. Corbariensis) which forms a low mound of wavy-edged evergreen leaves complemented by small, yellow-centred white flowers produced on mass in June and July. If you have a sunny sheltered spot Cistus x pulverulentus ‘Sunset’ is a fabulous low-spreading variety with felty grey-green leaves and small striking cerise coloured flowers, perhaps not as hardy as some varieties but if you have a suitable spot well worth growing. Cistus come from dry rocky areas, so they prefer well-drained soil in full sun; they are especially good for dry sunny banks where many plants struggle to thrive. After flowering trim their foliage lightly back to maintain their shape, cuttings can also be taken at this time to replace any old or woody plants which have lost their vigour.

Another shrub looking its best in June is Philadelphus or mock orange. Belle Etoile is a lovely variety with single creamy-white highly fragrant flowers borne on a reasonably compact plant to around 5ft or 1.5m. P.coronarius Aureus is a good choice for a spot in partial shade as its bright yellow foliage can scorch in full sun, as with most Philadelphus its creamy white single flowers are strongly scented.

An eye-catching evergreen flowering now is Crinodendron or Chinese lantern as they are commonly known, these are fabulous medium to large shrubs with narrow dark green leaves which provide the perfect backdrop for their crimson lantern-shaped flowers which open in from late spring and into the summer. Crinodendrons dislike drying out in the summer preferring moist but well-drained neutral to acid soil in a sheltered spot in the garden.

I often get requests for low-maintenance plants and a species that fits well in this category is Helianthemums which put on a fabulous show at this time of year. Heliathemums or rock roses are tough little members of the cistus family they form an evergreen carpet of green or silvery leaves which are covered in a glorious display of flowers from spring to midsummer. They are widely available and there is a good range of colours and varieties to choose from, among my favourites is H.’Ben Fhada’ which has bright yellow flowers with a golden blotch in the centre of each petal,  H.’Supreme’ is another fabulous variety with its vibrant magenta-red flowers also H.’Prima Donna’ with its pale pink flowers which blend well with its silvery foliage. Heliathemums thrive in well-drained soil in full sun, trim after flowering to keep tidy and get a possible second flush of flowers in late summer.

Coreopsis are easy-to-grow perennials which have been a summer favourite for gardeners for many years due to their unfussy nature and bright colourful flowers borne over a lengthy period. There are many good well well-established varieties such as the compact ‘Early Sunrise’ the slightly taller ‘Sunray’ and the verticilliatas with their masses of flowers on wiry stems with elegant slender foliage. More recently there have been some exciting new introductions including a new range called the Li’l Bang™ series which grows to only 20 – 30cm tall, flowers profusely and have good disease resistance. C. Li’l Bang Daybreak forms a neat mound of finely cut green leaves with large single bright red flowers which have a striking yellow edge and centre, as with the others in this series the flowers are sterile so do not set seed-making deadheading less important to keep the show going. Other good varieties in the series are C. Li’l Bang Starstruck which has the same deeply cut foliage but with large lavender flowers which have variable white tips and yellow centres and ‘Enchanted Eve which has burgundy centres to its flowers with yellow edges. Coreopsis grows well in in a sunny site in best to well-drained soils and also makes good container subjects, they are also attractive to bees and butterflies and resistant to deer.

Not all thistles are invasive weeds and the popularity of cultivated varieties has increased over recent years with them appearing in gardens at Chelsea and other flower shows, Cirsium rivulare ‘Atropurpureum’ has become particularly popular with its eye-catching deep crimson flowers held on erect stems from early to mid-summer and can bloom again if cut back after its first flush of flowers. A more recent introduction is C.r.’Trevors Blue Wonder’ which has the same basal rosette of spiky leaves as atropurpureum but with flowers of a deep rich purple with a bluey hue and like all thistles these are a magnet for butterflies and bees, its growth is slightly more vigorous and stems a little stiffer although all the varieties hold up well. Another recently introduced variety is C.r. ‘Frosted Magic’ which is a useful addition with its creamy white flowers adding to the colour range of these attractive clump-forming plants, like all the rivulare varieties it enjoys full sun or light shade and grows best in moist or moist but well-drained soil, very light or dry soils can result in powdery mildew on the leaves. Overcrowded clumps can be lifted in autumn or spring and divided every few years; they make excellent companions for grasses and other cottage garden plants such as Astrantia, Salvia and Papaver.

Many southern hemisphere plants have become commonplace in our British gardens despite our weather sometimes being a little harsher than their native land, Libertias are one such genus of plants which have adapted well, enhancing our gardens and are becoming increasingly well known. One of the strongest growers is Libertia grandiflora, this New Zealand native forms a good clump of sword-shaped grass-like evergreen foliage from which in spring and early summer numerous flowering stems emerge carrying several clusters of buds which open into pure bright white three petalled flowers, these are followed by orange-brown seed capsules. Another interesting garden-worthy Libertia is L. sessiliflora ‘Caerulescens’ a smaller plant than L. grandiflora with stiff upright bluey-green sword-shaped leaves complimented at this time of year by a profusion of china blue flowers with yellow stamens. A libertia with more winter interest is L. peregrinans, a smaller eye catching Libertia which has stiff narrow upright golden-green leaves which are shaded with orange, particularly in the cold winter months. This rhizomatous perennial has small white flowers in early summer followed by small seed capsules full of orange seeds. Libertia thrive in full sun but will tolerate some shade and grow well in most soils but resent too much wet, they are relatively untroubled by pests but may need some tidying in spring to remove some of the older growth which has become untidy throughout the winter.

Question for Keith

I have two standard Olives in pots, when is the best time to prune them and how much?

I like to prune Olives in late spring to early summer but any time up to the end of August would be ok, it is best to avoid pruning in the colder months as this could lead to infection. As yours are in containers prune to keep the heads the size you require but first remove any dead or diseased wood and any crossing or rubbing branches then try to open up the centre of the tree to allow in light and air, following this the stems can be reduced by up to a third to maintain the shape and size of the tree.

My strawberry tree (Arbutus unedo) has developed lots of dark spots on its leaves is there anything I can do to get it looking good again?

There are a couple of fungal diseases which attack Arbuus, the most prevalent being Elsinoë mattiroloanum which attacks twigs as well as the leaves. It is best to remove and destroy all the infected plant material if possible then spray with a fungicide for ornamental plants as directed, spray a small area first to ensure the plant is not affected by the chemical. The plant can also be given a feed with a good slow-release fertilizer then mulched well around the roots, hopefully, this will get the plant growing strongly again and help prevent reinfection.

The leaves of my Phlox plants are narrow and distorted, what could have caused this?

Your phlox is probably suffering from Phlox eelworm which infects and fattens the plant’s stems and shrinks and distorts the leaves. Although there is no chemical control available to gardeners there is a solution, because the microscopic eelworm attacks the stem, not the roots your Phlox can be propagated by root cuttings (not division) before growth starts in spring should you wish to save the variety, the rest of the clump should be removed and burned or discarded and any new Phlox should be planted in fresh soil well away from where the infected clump was growing.

Is it possible to grow Raspberries in pots?

Yes, Raspberries can be grown in pots; in my opinion, autumn fruiting varieties are the best and will fruit a year earlier than summer varieties. Plant from November to March in a 50/50 mix of multi-purpose and J. Innes compost in a pot at least 45cm wide and deep. Good varieties include Autumn Bliss, and Polka which fruits slightly earlier or for something slightly different try All Gold a yellow fruiting variety. Feed regularly with a high potash fertilizer in the growing season, at the end of the year cut back the stems to ground level then in spring leave the 2 or 3 strongest stems to grow for next year’s crop.