General High-performing Ilex crenata varieties for every garden


During covid times, Bokrijk has become a particularly popular walking destination, where visitors enjoy the open space, the historic setting of the Open Air Museum, and the lush greenery. That greenery is now receiving extra attention from scientists. The Bokrijk Arboretum in fact houses an exceptional collection of varieties of Ilex crenata or Japanese holly, a species often used as a substitute for boxwood. The plants in Bokrijk, together with plants from the Leen arboretum in Eeklo, are screened for useful properties, such as disease resistance and tolerance to less acidic soils. The aim is to use plant breeding to develop new cultivars that can be used even more widely in all kinds of gardens and are therefore less dependent on the right type of soil (acid - non-acid, heavy clay - sand, dry - wet).

This scientific project with ILVO and KU Leuven is being carried out at the request of ornamental plant cultivation company Plant Select, and therefore has a co-creative set-up with a view to accelerated innovation and added value creation. "This acceleration is necessary in order to be able to respond to an opportunity in the market, because breeding is usually a long process," explains researcher Esther Geukens.

This acceleration is necessary in order to be able to respond to an opportunity in the market, because plant breeding is usually a long process.

Esther Geukens (researcher)

Soft and snuggly holly

The small-leaved or Japanese holly (Ilex crenata) looks nothing like the classic spiny holly, but it does resemble boxwood enormously, without being bothered by fungal diseases or box moth infestations. It is therefore not surprising that, parallel to the search for disease and pest resistant boxwood, work is also being done on well-performing Ilex alternatives. At Plant Select, a leading Belgian company in the cultivation of Japanese holly, cultivation is on the rise. With Ilex crenata Blondie and Dark GreenĀ®, the company has its own selections of Japanese holly under the Ilex Select label, which have already found their way to the European market in millions of plants. For the expansion of the range of Ilex crenata, Plant Select is calling on the experience in ornamental plant breeding at ILVO and on the expertise within KU Leuven.

holly that looks like boxwood in a pot
Ilex crenata.

Valuable collections

Within this research ILVO and KU Leuven make grateful use of the Ilex crenata collection in the Arboretum of Bokrijk. In the meantime, material from nearly one hundred different Ilex crenata genotypes has been collected in the collections of Bokrijk and Het Leen in Eeklo, among others. Bokrijk is happy to cooperate with the study.

In our arboretum you will find one of the largest collections of the Ilex crenata in Europe. In addition, we are recognized as a testing ground by the American Holly Society. It is therefore natural that Bokrijk is happy to cooperate with this research as part of its social role,

Igor Philtjens (president of Bokrijk)

Selection to new Ilex

The doctoral research aims to select plants with an improved resistance to abiotic (weather conditions, soil conditions, etc.) and biotic (diseases and plagues) stress. When planting, gardeners often fail to take into account the specific needs of certain plants (soil, sun, moisture), which makes it more difficult for them to develop in all their glory. Japanese holly does not fare as well in soils with a higher pH (opposite of acid), and in wetter soil types it is also more susceptible to a soil fungus (Berkeleyomyces basicola) that affects the health of the root. The research will initially focus on the genetic variation within Ilex crenata, then a test plot with differences in soil acidity will be established on the farm to evaluate the pH sensitivity of Ilex crenata genotypes over several years. A bio test will be developed for the fungal disease. The project runs until 2024.

Arboretum bokrijk.
A panoramic view of the Arboretum at Bokrijk.
Ilex buergeri
A group of Ilex buergeri plants, a rare bush or tree shaped Chinese species, growing at Bokrijk.