The Kumson Forsythia (Forsythia koreana ‘Kumson’) is a distinctive deciduous shrub offering a twist on the traditional spring-blooming forsythia. Unlike its common relatives, ‘Kumson’ features remarkable variegated foliage that provides multi-season interest. The leaves emerge deep green, intricately etched with a network of silvery-white or gold veins. Before the foliage fully emerges, the plant displays typical early spring bright yellow, bell-shaped flowers along its stems. This combination of showy blooms and unique, patterned leaves makes the Kumson Forsythia a highly sought-after specimen.
Site Selection and Initial Planting
The Kumson Forsythia is winter hardy in USDA zones 5 through 8, making it suitable for a wide range of climates. To achieve the best flowering and most vibrant foliage variegation, plant the shrub where it receives full sun (at least six hours of direct sunlight per day). While it tolerates partial shade, too much shade diminishes the amount of bloom and causes the distinctive variegation to fade, resulting in greener leaves.
The ideal soil is moist but well-drained, as Kumson Forsythia does not tolerate standing water. If the existing soil is heavy clay, amend it with organic material like compost to improve aeration and drainage. When planting, dig a hole slightly wider than the root ball but no deeper, ensuring the top of the root ball remains slightly above the surrounding grade. Before placing the plant, gently loosen any tightly circling roots to encourage outward growth.
After setting the shrub in the hole and backfilling with soil, water the plant deeply to settle the soil and eliminate any air pockets around the roots. For the first growing season, newly planted Kumson Forsythia requires consistent and regular watering to establish a robust root system. This initial routine is crucial for establishment, but it is important to avoid daily watering, which can lead to root rot.
Essential Seasonal Maintenance
Once established, Kumson Forsythia exhibits drought tolerance but benefits from deep watering during extended dry periods, especially in summer. Supplemental water helps maintain active growth, which produces the newest, most colorful variegated foliage. Always water the ground at the base of the plant rather than the foliage to minimize the risk of fungal diseases.
Fertilization should be approached with restraint, as forsythia shrubs are not heavy feeders and often perform well in average garden soil. Over-fertilizing, especially with high-nitrogen formulas, can stimulate excessive leafy growth at the expense of flower bud development, reducing the spring bloom display. If the soil is poor, apply a balanced, slow-release fertilizer in early spring before new growth begins, or simply top-dress the area with a layer of quality compost.
Mulching around the base of the shrub is highly beneficial for conserving soil moisture, moderating soil temperature, and suppressing weeds. Apply a layer of organic mulch, such as pine straw or shredded bark, a few inches deep, but be sure to keep the mulch pulled back several inches from the main stem of the plant. This practice prevents moisture from accumulating directly against the trunk, which can cause rot or invite pests.
The foliage can be susceptible to scorching in intense afternoon sun, particularly in warmer climates. Planting ‘Kumson’ where it receives morning sun followed by afternoon shade protects the leaves and preserves the clear definition of the gold-veining. Continuous monitoring for new growth is recommended, as the best foliage color is often found on these newer shoots.
Pruning for Health and Bloom
Since forsythia blooms on wood grown the previous season, timing is paramount to avoid removing the next year’s flower buds. The correct time to prune is immediately after the spring flowering has finished, before the shrub focuses energy on new vegetative growth. Pruning later in the season, typically after mid-July, removes the developing flower buds for the following year.
The preferred method for established shrubs is a technique known as renewal pruning, which promotes new, vigorous growth from the base. This involves selectively removing the oldest, thickest canes, cutting them back to the ground. A general guideline is to remove approximately one-third of the oldest, largest stems each year. This systematic removal encourages the production of younger stems, which are the most floriferous.
Forsythia should not be sheared into a formal shape, as this removes the graceful, arching habit of the stems and leads to dense, non-flowering outer growth. Instead, focus on thinning congested growth in the center of the bush to improve air circulation and light penetration. The ‘Kumson’ cultivar often has a more restrained form than standard varieties, meaning it may require less aggressive pruning. Out-of-shape or wild branches can be cut back to a lateral branch or removed entirely at any time.