How to grow and care for stock flowers

Stock flower (Matthiola incana), also known as gilly flower or hoary stock, is a hardy biennial plant that brings splashes of colour and a sweet and spicy fragrance to a cottage or informal garden. With clusters of blooms forming a frilly spire of petals and soft narrow green-grey leaves, it also makes a long-lasting cut flower. The species is native to southern Europe and has purple flowers, but many single- and double-flowered cultivars have been developed in a range of colours, from white and yellow through every shade of pink, to red and purple. Stock flower attracts pollinating insects to the garden.

Stock flower is biennial, meaning it has a two-year life cycle. In the first year, the summer-sown plant develops roots, stems and leaves and survives through winter. In the second year it flowers and sets seed before dying. Stock flower is hardy, tolerating all but the hardest frost.

How to grow stock flowers

Grow stock flower from seed and plant in full sun in an informal flower border. For a bushier plant with more flower spikes, pinch out the growing tip in spring. Deadhead throughout summer and, when the flower display is over, dig up the plant and add it to your compost heap.

Where to grow stock flowers

Grow stock or gilly flower in full sun unless you get extremely hot summers, where partial shade – with morning sun only – might provide more favourable conditions. It does well in a sheltered spot in moist, well-drained soil and is suitable for a container or a flower border. Plant taller cultivars (up to 60cm) in the middle of a border, shorter ones towards the front. Grow them close to seating areas, so that you can appreciate their sweet and clove-like scent. Stock flower, like the rest of the cabbage family, does not thrive in acid soil.

How to plant stock flowers

Stock flowers are easy to grow from seed. In early summer, sow stock seeds in a tray, scattering them thinly on the surface of a sowing compost and covering with a sprinkling of vermiculite (light helps germination). Cover with a transparent sheet and maintain a temperature of 18-20 Cº until germination about ten days later. When the seedlings have two true leaves, prick them out into pots and grow them on. In early autumn, when they are 8-10cm tall, plant them where you want them to flower the next year.

Alternatively, sow stock seed directly into the flower bed in early summer, lightly rake over them and settle them into the soil by watering them in using a watering can with a rose attachment. When the seedlings have several leaves, thin them to 25cm apart. They will overwinter in the garden and flower the following summer.

Plant out your seed-grown stock flowers (or plug plants from a nursery) in September, when the soil is still warm. They will continue to grow roots and leaves up until the first frosts and will then flower the following spring and into summer.

In areas that get really harsh winters, protect the plants in a well-ventilated cold frame, glasshouse or unheated conservatory, and plant them out in spring.

Use a trowel to dig a hole twice as large as the root ball, set the plant in gently and back fill the hole with soil, firming it down with your fingers, so that the lowest leaves are level with the soil surface. Space your plants at least 25cm apart. Water in gently.

How to care for stock flowers

In the second year, in spring, pinch out the growing tip of the plants to encourage branching, which results in denser foliage and more flower spikes. Water regularly in dry conditions, especially at the seedling stage, taking care to water the soil, not the leaves of the plants. Cut back stock flower after flowering and at the end of the season pull or dig up the plants and add them to your compost heap.

How to propagate stock flowers

Instead of cutting back all the spent flower spikes, leave one or two to produce seed. They will form long narrow seed capsules along the stem. When they are ripe (they will turn from green to brown) pick the capsules and lay them out to dry somewhere warm indoors. When they split, collect the seed and store it in a labelled envelope. A word of warning: they may not produce flowers of the same colour or form as the parent plant, due to cross pollination.

Pests and diseases

The soft velvety leaves of stock flower are susceptible to mildew, so make sure the seedlings are well-spaced and well-ventilated. Make sure you give each plant enough space in the border, and avoid getting the leaves wet when watering.