Lars Lund

16 Aug 2022 14:18

The holiday continues

By Lars Lund


It is nice to have a greenhouse to grow tomatoes, cucumbers, peppers, aubergines and exotic trees such as apricots, grapes, citruses and olives. It reminds us of vacation.

The climate has changed, and I cultivate a lot of tomatoes out in the open. For this reason, there is more room for other and more exotic plants in the greenhouse, but I also cultivate exotic trees outdoor in the garden. To have exotic trees also helps lifting the mood and the taste experience.


Two trees I like are the heartnut and the mulberry tree. Both trees and especially, the mulberry tree is something special. The tree needs a warm climate, therefore, it is difficult to cultivate the tree in Scandinavia – and no further north than south Scandinavia.


The mulberry tree is usually cultivated in Syria, Iran and the southern parts of Europe, where the silkworms feed on the leaves of the mulberry tree and spin their silk. In these parts it is the white mulberry that is cultivated, which cannot be grown in the Danish climate. The Latin name is Morus alba and it originally comes from China. Instead, we can cultivate the black mulberry tree, which also looks better. It will reach a height of 5-6 meters, but it is no problem if you want to prune the tree. Prune it at the top, while the tree is still young. The tree has beautiful heart shaped saw-edged leaves, but the leaves can also be formed as figs or in other shapes. The branches form a beautiful top, and the tree is also ideal for a small garden.

The fruit tastes great. It tastes a bit like blackberries and in the beginning they are red and then they turn black when ripen. They should be eaten right away, otherwise, it can be used in marmalade or juice the same day they have been picked.

There are white and black mulberries, and moreover, there are also a red one which originates from the East Coast of the United States and are also cultivated in the southern part of North America. Taste wise, the black one is the best. Unfortunately, the birds agree.


This fruit is what you call a false fruit. Most species are self-pollinating this includes black mulberries. It may take a while before the tree starts producing fruit, but patience is rewarded. Once it has started producing berries, it will produce year after year.

When the tree is transplanted, it must be somewhere warm and sheltered. The soil should be calcareous, and preferably moist – but not too wet.


When cultivating in Denmark and places with similar climate, Morus nigra is recommended. It is a small and pretty tree. White mulberry (Morus alba) produces black fruits despite the name. The growth of this is not as attractive as the black mulberry. Illinois Everbearing is an American hybrid which is hardy and very fertile.

Walnut in a heart shape

The common walnut is originally from Persia, but it was brought all the way to Denmark and western parts of Norway.


Grafted trees are fast to give yield, but it is a demanding process. When grafting trees, the temperature should be between 25-27 degrees. For this reason, grafted trees are quite expensive and the selection is limited. On the other hand, a lot of seed propagated plants can be bought, but you will have to wait years before they bear any fruit. Therefore, look for those that are grafted. Grafted trees start to bear fruit when they are young plants.


Walnuts are self-pollinating. However, some develop the male and female blossoms at different times, which makes the pollination impossible. If you have room, it is best to plant two different varieties just to be sure. The tree is pollinated with the help of wind, so the tree is not dependent on bees to be pollinated.

During October the walnuts ripen and fall from the trees. Nuts from the best sorts will fall down without the green shell. The sorts that ripen later tend to still have the shell or parts of the shell. After the harvest, it is important to dry the nuts as soon as possible, otherwise, they will mould. The best place to dry them is in a warm and ventilated place on top of some papers or mesh bags. At a factory the nuts would be washed in a mixture of chlorine and atamon, but if they are dried right away it should not be necessary. Alternatively, you can crack the nuts and freeze them.


Heartnuts are new on the market. They belong to the family Japanese walnut ‘Juglans Ailantifolia’. The cleaning process of these nuts is more extensive than it is for common walnuts, but it is worth it. The taste of the fine heart-shaped nuts is mild and sweet, and they can last for many years without getting stale, as they have a high content of antioxidants. The Swedish Kalmar is a nice sort for our climate, also the Canadian CW3 has shown to be hardy and gives a good yield. Heartnut trees will not get as tall as common walnut trees, but it will get just as wide.


You can also read the article “prolong your holiday in your greenhouse”