Forsythia

Light and exposure

Forsythia flowers best in full sun. The sunnier the spot, the denser and more golden the late winter display along the whole length of the branches. In shade or part shade it grows perfectly well but flowers noticeably less, with branches reaching for the light instead of covering themselves in flowers.

It copes equally well with a windy corner or a sheltered garden, which makes it valuable where other shrubs refuse to settle. It is the classic shrub for an informal hedge. One qualification in climates with scorching summers: light afternoon shade keeps the foliage from burning and costs almost nothing in flowering.

Watering

Once established, forsythia needs almost no watering at all. It is a tough shrub that draws moisture from deep in the soil and copes very well with summer drought, even through increasingly dry summers.

Only the first year after planting deserves some attention: water a young plant once or twice a week during dry spells while its roots settle in. After that, short of a truly severe and prolonged drought, it manages on its own. Few gardeners make the link: a severe midsummer drought thins out the following year’s display, because that is exactly when the flower buds are formed.

Soil and repotting

Forsythia is not fussy about soil type. It grows equally well in clay or chalky soil, in poor ground or richer ground, as long as it is not permanently waterlogged.

Ordinary garden soil suits it with no special amendment. A little compost at planting helps it get going, but it is not essential for such an undemanding shrub.

Temperature and humidity

Forsythia is completely hardy as far as its wood goes: it shrugs off frosts of minus twenty-five degrees without damage and needs no winter protection at all, from USDA zone 5 to zone 8.

Its weak point is not cold, it is the timing of its flowers. The flower buds freeze long before the wood, at around minus twenty degrees: after a very cold winter the shrub is alive, green and perfectly healthy, but completely devoid of flowers. Where winters regularly drop below that threshold, choose a cultivar selected for bud hardiness, such as 'Northern Gold' or 'Meadowlark'. And everywhere, a late frost falling on flowers that have already opened browns them and shortens the display by a few days: the shrub itself is never harmed, only the look of it suffers for a while.

Pruning and upkeep

This is the single most important thing to know about forsythia: it flowers on wood it produced the previous year. In practical terms, the buds for the next display form as early as this summer on this year’s shoots. Pruning in winter or very early spring, before flowering, means cutting off the flowers to come.

The rule is simple: prune only in the two or three weeks that follow the fall of the last flowers, never before. Shorten the branches that have just flowered and even out the shape. On an old shrub that has gone bare at the base or grown too big, cut back a third of the oldest stems right to the ground every two or three years: the shrub comes back stronger, with young wood and a renewed display of flowers.

Pests and diseases

Forsythia is a healthy shrub that causes very few problems. That is one of the reasons for its success in gardens and hedges just about everywhere.

You occasionally see dieback on weakened shoots, or forsythia gall, woody swellings that appear on the stems without necessarily threatening the plant. In both cases it is enough to cut out and remove the affected parts during the yearly pruning. No routine treatment is needed on a healthy shrub.

Propagation

Taking cuttings is the simplest and most reliable way to multiply a forsythia. In autumn, cut a length of this year’s growth, fifteen to twenty centimetres long, and plant it straight into open ground, somewhere sheltered from the wind. It roots almost automatically, no rooting hormone or greenhouse needed, a real gift for anyone wanting to fill out a hedge cheaply.

Forsythia also layers itself: low branches that touch the ground root naturally at the point of contact. Just look for these spontaneous layers at the foot of an old shrub, separate them from the parent plant once rooted, and replant them wherever you like.

Month-by-month care calendar

Green Hub tips

• Never prune forsythia in winter or early spring: the following season’s flowers are already forming on last year’s wood, and pruning too early removes them all.
• The only real pruning window is right after flowering, in the two or three weeks that follow the fall of the flowers. Once that has passed, leave the shrub alone until the following year.
• An old, bare forsythia comes back stronger if you cut a third of its oldest stems right to the ground every two or three years.
• To multiply a forsythia for free, simply plant a length of this year’s growth straight into open ground in autumn, it roots on its own with no special care at all.