When large numbers of new shrubs are needed - perhaps if moving house or starting a new garden, then consider growing them from seed; it’s the cheapest way, although considerable advance preparation is needed to have plants ready for planting out at the time of the move.
Although many shrub seeds have complex germination requirements, some are very straightforward: seeds of Leycesteria and Lavatera, for example, need no pre-treatment.
Pea-family shrubs such as the brooms (Cytisus, Genista, Spartium) grow quickly and flower from an early age, but their hard seed coats need either ‘chitting’ (softening with a hot water soak before sowing; see below) or carefully removing part of the hard seed coat with a sharp knife, or erasing it with sandpaper.
Pre-sowing hot water treatment for pea-family shrubs
E.g. (Colutea, Cytisus, Genista, Spartium, Lespedeza, Lupinus, Robinia) Place the seeds in a heat-proof container. Pour just-boiled water over the seeds and allow them to cool; do this three times.
General sowing technique for shrub seeds
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| Sow the seeds thinly, with a finger-width between each seed, or sow one or two per module (depending on the size of the modules). | Large seeds require covering with sieved compost, vermiculite or perlite. Small seeds do not need covering and in fact some, such as Paulownia, need light in order to germinate, so are best left uncovered. | Prevent pots from drying out by covering with an inflated polythene bag secured with a elastic band, or with a suitable cloche (half a clear plastic bottle works well). Trays can be covered with a clear plastic lid, or with a sheet of glass or perspex. |
When large enough to handle, transplant/prick out each seedling in its own pot of multi-purpose compost.
Seedlings in shallow seed trays need transplanting promptly, handling them carefully by holding the seed leaves, rather than the emerging true adult leaves. Seedlings in modules can be left a little longer before transplanting, allowing their roots to fill the module, and then transplanting the whole plug of roots and compost in one go.
Water regularly, as needed, and feed with liquid fertiliser every month, growing the seedlings on into small plants.
The following spring or summer, when the plants are more robust, start to introduce them to outdoor conditions, a process known as hardening off. Start gradually, in a sheltered position for a couple of hours during the warmest part of the day, progressing towards leaving them out 24 hours a day in the pots.
Plant them out into the garden in the autumn, giving them the winter to settle their roots into the soil before coming into active growth the following spring.
Easy shrubs from seed
- Abutilon vitifolium A large (3m/10ft), quick-growing deciduous shrub, for mild southern areas, with abundant mauve flowers in spring or early summer and grey/green vine-shaped leaves
- Clerodendrum trichotomum Glory tree Up to 4m (13ft) with white star scented flowers followed by amazing blue berries in a crimson calyx. Deciduous.
- Colutea arborescens Large (3m/10ft) deciduous shrub with yellow summer flowers but really grown for its inflated seedpods. Pea family.
- Cytisus multiflorus (syn. C. albus ) white Spanish broom A medium-sized slender deciduous shrub with white flowers in late spring and early summer. Pea family.
- Genista aetnensis AGM Mount Etna broom Very large (8m/27ft) deciduous shrub or small tree with abundant yellow flowers in late summer. Pea family.
- Hypericum olympicum AGM Easy-to-grow deciduous ground cover with bright yellow summer flowers (up to 30cm/12in).
- Lavatera arborea tree mallow Short-lived, evergreen perennial reaching 3m (10ft) and bearing masses of purple-pink flowers throughout summer. Only for mild districts, but ideal for coastal gardens.
- Lespedeza thunbergii AGM bush clover Large deciduous shrub for warm sunny sites with purple trusses of flowers at the end of graceful weeping branches. Pea family.
- Leycesteria formosa AGM Himalayan honeysuckle Deciduous, quick growing with green bamboo-like shoots up to 2m (6.5ft) tall with wine coloured tassels from which flowers and purple berries, much relished by birds, follow.
- Lupinus arboreus AGM tree lupin A medium (2m/6.5ft) evergreen or semi-evergreen shrub with spikes of yellow summer flowers for acid and dry soils. Pea family.
- Paulownia tomentosa AGM A large deciduous tree grown as shrub (2m/6.5ft) for the huge leaves produced if cut back to a stump each winter.
- Spartium junceum AGM Spanish broom Large upright, deciduous shrub (3m/10ft), yellow flowers in summer, ideal for poor soils. Drought resistant. Pea family.
Shrub seeds can be bought from Chiltern Seeds and can also be obtained from the RHS Seed Distribution List (available November - January; RHS members only).
Maya Albert & Guy Barter