About ten species of deciduous shrubs, originating in Asia, belong to the genus forsythia; the most commonly cultivated is a hybrid between F. suspensa and F. viridissima. The zabel forsythia is a fast-growing shrub, which can reach 3-4 meters in height.
It constitutes a fairly informal bush, with erect stems, poorly branched, brown in color; the foliage is green, oval or lanceolate, develops after flowering. The forsythias bloom in late winter, between March and April, producing numerous golden-yellow flowers that bloom along the branches of the previous year.
Over time they tend to lengthen the branches very much, so it is advisable to shorten the branches a little after flowering, cutting some of the old branches that have already bloomed to the ground.
The Forsythia intermediate does not fear the cold; this type of shrub has a very rustic character.
This variety of plants prefers sunny, or semi-shaded locations.
A poorly sunny position can cause scarce or even absent blooms, although the plant, being very resistant, will survive even in these conditions. The Forsizia di zabel does not fear the wind, so it also adapts to the exposed areas; if the intensity is rather strong, then the flowering will be less luxuriant.
These shrubs, if grown in the open ground, are generally satisfied with the rains.
As soon as they have been planted, a watering is required that bathes the soil in depth; specimens grown in a container may need watering in the event of prolonged drought as they cannot benefit from the moisture naturally present in the soil.
The Forsizia di zabel is more affected by the possible water stagnation that can form on the ground than by the lack of water.
The Forsythia x intermedia adapts without any problems to any soil, preferring nevertheless soft and humus-rich soils, very well drained. It fears water stagnation, so it is good to mix a good quantity of sand with the growing medium so as to guarantee the right degree of drainage. For this reason it would be better to avoid soils that are too rich in clay.
The multiplication of this plant usually takes place by using talle preparation or through the offshoots.
It is also possible to rely on seeds to get new plants; seed propagation can be carried out in spring, although the resulting specimens are not always identical to the plant that gave the seeds.
The pruning of this plant should be done after flowering, shortening the branches that carried the flowers and eliminating the dry or woody ones, without buds. Winter pruning is to be avoided.
Forsythia of Zabel - Forsythia x intermedia: Parasites and diseases
This shrub is very resistant but can be hit by root rot caused by dangerous stagnant water.
Sometimes the mites conspicuously ruin the foliage.
Before flowering it could be useful to provide a preventive treatment with specific insecticidal and pesticide products so as to protect the intermediate Forsythia from possible attacks.