How to grow philadelphus

What are Philadelphus?

These easy-to-grow shrubs produce clusters of white flowers in early summer. These only last for a few weeks, but usually perfume the air beautifully, creating a lasting impression in early summer.

Choosing the right Philadelphus

The vast majority of Philadelphus are hardy so can be grown throughout the UK. As a result, the main choices come down to selecting a plant that will be the right size for your garden, as well as choosing a flower form you particularly like. If you go to a nursery or garden centre in early summer, you will often see the plants in bloom, which can be more helpful than looking for pictures in books or online, since you can smell them too!

Eventual size

The most important thing is to select a cultivar

Gardeners often use the word variety when referring to a specific plant, but the correct botanical term is 'cultivar'. Whichever word you use, it means a distinctive plant or plants, given a specific cultivar name and usually bred to enhance certain characteristics, such as flower or fruit size, colour, flavour or fragrance, plant size, hardiness, disease resistance, etc. Additionally, it is worth knowing that, botanically, variety has another meaning - it refers to a naturally-occurring distinct plant that only has slight differences in its looks. For example, Malva alcea var. fastigiata differs from typical plants by having an upright habit.

with an eventual size that will suit your garden.

• Large cultivars reach around 2.4m (8ft) tall, so are suited to the back of borders, or can be used as a substitute for a small tree in a tiny garden. A popular example is Philadephus ‘Beauclerk’
• Medium-height Philadelphus, for example P. ‘Belle Etoile’, which grows to around 1.5m (5ft), are ideal for planting behind other summer-flowering shrubs such as roses, or growing among tall perennial
  

  Perennials are plants that live for multiple years. They come in all shapes and sizes and fill our gardens with colourful flowers and ornamental foliage. Many are hardy and can survive outdoors all year round, while less hardy types need protection over winter. The term herbaceous perennial is used to describe long-lived plants without a permanent woody structure (they die back to ground level each autumn), distinguishing them from trees, shrubs and sub-shrubs.

  plants
• Small cultivars with compact and weeping habits include P. ‘Manteau de Hermine’. These are around 75cm (30in) tall and good at the front of a border or in a large container

Flowers and foliage

As far as flower differences go, some are double or have coloured centres, but generally, the overwhelming impression is of a profusion of white blooms. Choose one that appeals most.

If you like coloured foliage, there is the golden form P. coronarius ‘Aureus’ and also a variegated

Variegated means having leaves or other plant parts with streaks, blotches or patches of different colours. Typically, these would be a combination of two colours, such as green and gold or green and white.

form, P. coronarius ‘Variegatus’.

Buying a Philadelphus

These shrubs can be bought from garden centres and nurseries as container-grown plants. They are normally for sale in 2-litre pots, but larger sizes are sometimes available in garden centres and nurseries, and from online suppliers, with a larger choice available by mail order.

Plants can sometimes be bought bare-root

These have been lifted from the ground while dormant, with little or no soil around their roots. Various plants may be available bare root, including fruit trees, hedging plants and some perennials. They are generally cheaper than plants in containers, but are only available in winter/early spring, while dormant

in the dormant season (winter), usually by mail order. These are ready for immediate potting up or planting out.

Buying: garden centre plants

Buying: trees and shrubs

When to plant

• You can plant container-grown plants at any time of year, but they establish best when planted in autumn or spring
• Plant bare-root
  

  These have been lifted from the ground while dormant, with little or no soil around their roots. Various plants may be available bare root, including fruit trees, hedging plants and some perennials. They are generally cheaper than plants in containers, but are only available in winter/early spring, while dormant

  plants in the dormant season (winter), when the ground is not frozen or waterlogged. Alternatively, pot up into a container to grow on

Where to plant

Choose a sunny or semi-shaded site in fertile, well-drained soil.

• Avoid planting golden-leaved forms in full sun as it can damage foliage
• Check on the label for eventual width of the plant, to give plants enough room
• Also check eventual height when considering placement, as some are short and suitable for the front of the border, while a few can grow to the height of a small tree

How to plant

Plant container-grown and bare-root Philadelphus as you would any shrub, by digging a hole deep enough to take the rootball

The roots and accompanying soil when a plant is removed from a container or lifted from the ground.

, but around twice as wide as the rootball.

Improve the soil that goes back in around the sides of the rootball with well-rotted compost

Can refer to either home-made garden compost or seed/potting compost:

• Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own.

or manure. Water in well and keep moist if you plant in spring or summer. Mulching newly planted shrubs will help retain moisture in the ground.

If you’re unsure, follow our step-by-step guide.

Trees and shrubs: planting

Feeding

A general-purpose fertiliser, such as a handful of Growmore per square metre (sq yd), can be applied in spring if your plant needs a boost or the plant is growing on

Transferring young plants from one container to a slightly larger one, where they will have more room to grow and fresh potting compost. This encourages continuous, healthy growth.

poor soil.

Mulching

Applying a mulch

Mulch is a layer of material, at least 5cm (2in) thick, applied to the soil surface in late autumn to late winter (Nov-Feb). It is used to provide frost protection, improve plant growth by adding nutrients or increasing organic matter content, reducing water loss from the soil, for decorative purposes and suppressing weeds. Examples include well-rotted garden compost and manure, chipped bark, gravel, grit and slate chippings.

of organic matter is a good way to improve soil conditions and add some nutrients

To grow well, plants need a wide range of nutrients in various amounts, depending on the individual plant and its stage of growth. The three key nutrients usually taken up from the soil are nitrogen, phosphorus and potassium. Plants also need carbon, oxygen and hydrogen to make carbohydrates — their main energy source. Carbon and oxygen come from the air as carbon dioxide, while hydrogen is drawn from water absorbed by the roots. Other important soil nutrients include magnesium, calcium and sulphur. Most garden soils contain enough of these nutrients to support healthy plant growth.

. It also keeps weed competition down and preserves moisture in the soil.

Mulching

Watering

Once established, a Philadelphus shrub is unlikely to need watering unless your soil is very free-draining and there is a prolonged period of drought.

Watering

Deadheading

Philadelphus don't need deadheading

Deadheading is the process of removing spent flowers from plants to encourage more blooms and prevent seed production. This helps to redirect the plant's energy into producing more flowers rather than producing seeds.

, as they only flower once a year and removing the flowers doesn't improve the next flowering or promote growth in a noticeable way.

Pruning young plants

Cut out any dead, diseased or damaged branches after flowering. If there’s a branch that’s crossing through the centre of the plant, you might want to prune that out too – that way you’ll get an open shrub without congestion and branches that rub against each other.

Pruning established plants

Philadelphus are best pruned after flowering in summer. It’s not vital every year, but it does promote development of new flowering wood.

You do this simply by cutting back some of the older growth to new shoots lower down a branch, and by thinning

Pulling out some of the seedlings, usually along a row, so the remaining seedlings are spaced further apart. It reduces overcrowded, which can hinder their growth.

out from the base, removing a few of the older stems entirely (limit yourself to removing one in five each year).

Shrubs: pruning early-flowering

To make more plants, you can take softwood cuttings

Softwood cuttings are taken from spring to early summer (Apr-Jun), using material from the soft and flexible young shoot tips from this seasons growth, which root readily. Use for hardy and tender perennials, deciduous shrubs, climbers and some trees.

in early summer. They usually root quite easily, but won’t be ready to plant out in the garden until at least the following year. It will take at least two to three years before they start to flower, the display increasing as the shrub grows in size.

Cuttings: softwood

Philadelphus are generally free from disease, but aphids are a notable problem.

Both greenfly and blackfly can appear in early summer. You may notice these sap

Sap is a fluid that circulates through a plant's vascular system, in a similar way to blood moving through our veins. Phloem sap carries the sugars produced in the leaves by photosynthesis down to roots and other storage organs, as well as carrying minerals and hormones. Xylem sap is watery and transports nutrients absorbed by the roots upwards to the rest of the plant. Some plants leak sap from wounds or pruning cuts, and this is known as bleeding.

feeders when foliage starts to curl in response to their saliva. Interestingly, Philadelphus are one of the winter/spring hosts of the black bean aphid, the blackflies that can cover the tips of your broad beans a little later in the season. They don’t need to be controlled and are usually tolerated.

If you’re a member of the RHS, you can use our online Gardening Advice Service, via MyRHS, for any gardening queries and problems.