How to grow and care for stock flowers

Stock flower (Matthiola incana), also known as gillyflower or hoary stock, is a hardy plant which brings splashes of colour and a sweet and spicy fragrance to a garden. With clusters of blooms forming a frilly spire of petals and narrow green-grey leaves, it also makes a long-lasting cut flower. The species plant 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. Stocks attract pollinating insects to the garden.

Stock flower is usually a 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. Stocks are fairly hardy, but may suffer in very hard frosts.

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 stocks in full sun, but if your garden tends to get very hot in summer it may be better to plant them in partial shade to avoid the more intense midday sun. The plant does well in a sheltered spot in moist, free-draining soil and is suitable for a container or a flower border. Plant taller cultivars (up to 60cm) in the middle of a border, and shorter ones towards the front. Grow them close to seating areas so that you can appreciate their sweet, clove-like scent. Stock flower, like the rest of the cabbage family, does not thrive in acid soil.

How to plant stock flowers

Stocks are easy to grow from seed. In early summer, sow seeds in a tray, scattering them thinly on the surface of a sowing compost and covering with a light sprinkling of sieved compost or preferably vermiculite, which will let a little more light through, leading to better germination with these particular seeds. Cover with a transparent tray cover or lid and place them somewhere with some sunlight at a temperature of 18-20ºC, until germination about 10 days later. When the seedlings have two true leaves, prick them out into pots and grow them on. In early autumn, plant them where you want them to flower the next year.

Alternatively, sow seed directly into the flower bed in early summer, lightly rake over them and water very lightly using a watering can with a fine rose attachment. When the seedlings have several leaves, thin them to 25cm apart. They will overwinter in the garden and flower the following summer. Another way of sowing seed direct is to create shallow drills in the soil roughly 25cm apart, watering this, and then thinly sowing the seed into the drill and finishing by drawing a light covering of soil back over the seeds. The advantage of this method is that it makes it much easier to distinguish the seedlings from weed seeds, and the straight lines of seedlings are much easier to hoe around.

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 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, once the risk of very heavy frosts has passed in your area.

Use a trowel to dig a hole a little larger than the rootball, 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 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 flowers 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.