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Blackthorn Prunus spinosa – planting a primordial plum in the garden

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When Ötzi was killed on his last Alpine tour, he had eaten dried sloes, which were apparently a refreshing snack 5250 years ago. The blackthorn or sloe is common in our landscape as well as in our culture. Sloes are also the original prunes and primordial damsons; our modern plum and damson varieties are said to have originated from hybridisations of blackthorn with the cherry plum (Prunus cerasifera).

Blackthorns enrich the garden and landscape with their pioneering growth, which does not stop even in dry and stony places; blackthorns have almond-scented blossoms in March and April, which are even more impressive against the backdrop of the black bark, and they also develop deep blue fruits, which can be picked and enjoyed only after the effect of the first frost. In addition, the contradiction between the beautiful flowers and the very sharp, injurious thorns has fascinated folk beliefs and mythology for thousands of years: blackthorns are both a plant of danger (which can hurt and abduct, which is dominated by dark forces) as well as a plant of health and protection that guards us against this evil. This is also the equivalent in folk medicine, where infusions of blackthorn fruits, flowers and bark unfold their antipyretic and digestive effect. The blackthorn is also generally anti-inflammatory. And yes, medicine should also taste a bit bitter and astringent. ;-)

Blackthorn – which plants can I buy for my garden?

Those who have enough space and can tolerate suckers and are also interested in a deterrent effect can plant a wild sloe. It establishes itself very quickly in dry and stony soils and, after just a few years, forms suckers, which become simply impenetrable thanks to the pointed thorns. But, of course, smaller gardens may want to be more civilised and less dangerous to walk back and forth: therefore we have selected the large-fruited cultivars Reto, Godenhaus and Nittel for use in the fruit garden, which bring significant advantages compared to the wild species.
The benefits of large-fruited blackthorn varieties

  • Fewer thorns: the large-fruited varieties have fewer thorns.
  • No suckers: they are grafted on the weak growing rootstock St. Julien and no longer form suckers.
  • Earlier harvesting and processing: the new, large-fruited blackthorns Nittel, Reto and Godenhaus can also be harvested in September and October before the first frosts, as they do not necessarily need frosting to break down the bitterness and acidity to become edible. This feature is most pronounced in the Reto variety. For the other varieties, we still recommend waiting for the first frosts or, alternatively, freezing the fruits that are harvested early before processing them so that the reduction of the acidity and tannins is sped up.
  • Larger fruits: finally, the fruits of the cultivars are significantly larger and reach a diameter of about 2 cm (wild species about 10 mm).

So you have the choice: if you want a primeval wild plum that harbours the maximum of nature (insects, birds, butterflies) and almost does not let humans pass through, then the wild variety is the right plant for you. Ideally, the wild blackthorn is then used in a hedge with sea buckthorn, hazelnut, elderberries and other wild fruit. The planting distance for a dense hedge (which may consist only of blackthorns) should be about 150 cm.

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Picture: Blackthorn flower with a butterfly

If you like the bittersweet taste of blackthorns and would like to harvest fruits for processing, but do not have enough space and tolerance for a sprawling hedge, then choose the cultivars Reto, Godenhaus or Nittel. Note: it is best to plant two different varieties, as blackthorns are only partially self-fertile and tend to produce few fruits without pollinators. Alternatively, plums or damsons can fertilise their original form, the blackthorn.

Are blackthorns even edible?

Of course, blackthorns are edible, even if you would not think that in an early eating attempt in September or August. As already mentioned, Ötzi already knew that. There are few modern gourmets who would want to miss the characteristic taste, which always includes a bit of astringency and resistance: jams, fruit juices and also mixed recipes with other fruits abound. Producing blackthorn liqueur is also very common!

Nevertheless, the question of edibility is rightly asked since the early harvest the fruits of the wild bushes are inedible, too sour and too astringent; only after the first frosts do they become softer, more juicy, sweet/sour and easily digestible. The large-fruited varieties can also be harvested before the frost, but here, too, the fruit makes ripening progress after the frosts. Alternatively, the not quite ripe fruits in autumn can also be placed individually on a baking tray and then frozen. Ultimately, this has the same effect as natural frost; it softens the fruit, partially dissolves the tannins and eases the flavour – without losing the characteristic, tart aroma.

Are blackthorns poisonous?

The flowers and especially the seeds of the blackthorn fruits contain the poisonous cyanogenic glycoside amygdalin, which is neutralised with boiling and does not pose a risk. The hydrocyanic acid content of the blackthorn is generally rather low; it is much larger with almonds and apricots. If the sloes are put into brandy during the production of liqueur, part of the poisonous hydrogen cyanide precursor is left in the liqueur. This then leads to the typical bitter almond taste that characterises the popular sloe liqueur. The content of amygdalin is so low that it does not pose a risk. Ultimately, the hydrocyanic acid content is less toxic than the alcohol itself. ;-) In both poisons, the human body is able to reduce small amounts relatively quickly...the problem is, as always, the dose...
The blackthorn is poisonous in another sense, however: its side shoots, which are almost horizontal from the branches, have poisonous tips that can sting. This is not the only reason that blackthorn is also described in folk beliefs and mythology as being all sorts of black, threatening and dangerous things. And really: such a sting from a blackthorn, not disinfected, can quickly lead to a painful inflammation, especially on the picking hand. Therefore, we recommend the following: always wear robust and well-fitting gloves when handling blackthorns. And here is a second tip: the large-fruited cultivars have a lot less thorns than the wild species.

The blackthorn’s fantastic flowers

The following story also comes from mythology and a legend, which is apparently told in Poznan (and on Wikipedia...): the buckthorn mocked the thorns of the blackthorn, which had to justify Jesus’ painful crown of thorns. However, God thought that the accusation was unfair and, to make amends, let the white, beautiful flowers fall over the blackthorn in order to conceal the threatening thorns. These flowers, which cover the branches from top to bottom long before the leaves sprout and give off a characteristic, sweet almond scent, are really an absolute plus for this primordial plum! Incidentally, the flowers, like the fruits, the bark and the leaves, are also used for astringent teas and infusions that are said to reduce fever and inflammation.

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Picture: A bee on a blackthorn flower

Where do blackthorns grow and where is the best location?

Blackthorns – especially the wild species – are absolute pioneer plants that can easily establish themselves in dry and stony soil. They send out their roots and root shoots in order to occupy more space. They love a location in full sun or at most partial shade; they hate waterlogging and prefer a slightly alkaline soil.

Planting blackthorns

With the large-fruited cultivars, a location in full sun is even more important, even the demand for a fertile, moist soil is slightly greater if it is to produce good and high yields. Thanks to the grafting on the St. Julien rootstock, the soil tolerance of the varieties is greater, from slightly acidic to alkaline. In the case of a clearly acidic soil (pH below 6), lime should be added during planting.
We offer the wild form and the varieties Nittel, Reto and Godenhaus as strong container plants and the cultivated versions also as strong, 2-year-old plants in 10 L containers. These potted blackthorns can not only be planted at any time, they are already so well developed that they usually bloom and fruit in the garden in the 2nd year.

In an autumn planting starting from 1st October, we recommend shaking out the root ball completely before planting and stripping off all the remaining leaves on the plant. This ensures that the topsoil is in contact with the roots and that they start to grow out immediately. Directly in the topsoil, the sensitive roots (roots are the most sensitive organ of the plants) are also less sensitive to warm winter phases; as if the whole root ball is planted and the roots have too little time to root out. There is always the risk that the root ball warms up faster than the topsoil in nice winter weather and the plant perceives early spring signals and then gets damaged in a later cold spell. However, when planting from spring to the end of September, it is sufficient to tear up the root ball before planting it out.

Blackthorn growth

Blackthorns form bushes rather than trees. The large-fruited varieties Godenhaus, Reto and Nittel, which are offered in the Lubera® shop and are grown on St. Julien rootstocks, also develop into multi-branched shrubs rather than single-stemmed trees. The growth is accordingly rather sparse; the small side branches without a terminal bud, branch off the main shoots at almost a 90° angle, but with a pointed thorn at the end. The cultivars, however, have significantly fewer thorns than the wild plants.

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Picture: A blackthorn bush with ripe fruits

Pollination conditions for blackthorns

Blackthorns are only partially self-fertile. So if a blackthorn is all alone, there will only be small yields. Therefore always plant two different varieties, ideally at a distance of 2 - 3 m. It is also possible to plant blackthorns in the vicinity of already existing plum and damson trees, which they can also fertilise. Bees and bumblebees are responsible for the actual cross pollination, which like other insects and butterflies appreciate the early offer that the blackthorn provides.

Likelihood of confusion with blackthorn

The blackthorn can easily be distinguished from the hawthorn: the blackthorn blooms clearly before the leaves come out; the hawthorn blooms afterwards. Even with any poisonous plants, confusing the blackthorn is hardly possible: those who see the plum-like, small fruits that have a diameter of about 1 cm in autumn and in addition also feel the thorns, can be almost certain that they are standing in front of a blackthorn. Before the frost, the fruits taste like they are still very astringent. They only become edible after the frosts.

Pruning blackthorns

Well, especially with the wild blackthorns, I understand only too well that you will hardly dare to prune them. This is also largely unimportant, as the blackthorn hedge, planted with a spacing of about 150 cm, should also be impassable. At best, after 10 or more years, one should cut back such a hedge to the ground (to about 10 - 30 cm), in order to renew it and make it more vital again. Conversely, with the large-fruited cultivars, pruning is very much an issue, since one wants to harvest as many fruits as possible. In addition, old worn and hanging branches, which have almost no growth, should be removed to stubs in early spring so that new fruit shoots can arise.

Blackthorn/sloe – where does the name come from?

Blackthorns have a lot of names. The fact that they are thorny can be felt not only on the arms and hands when picking the wild shrub, but the Latin name (Prunus spinosa) also mentions the thorns. Why is the blackthorn black? Well, it cannot be due to the white flowers...the dark bark, however, was used in the Middle Ages to produce ink, which turned out to be less lightfast and was later replaced. In the age of Snapchat, where images and news dissipate shortly after their release, such an ink would certainly have its appeal. The name “sloe” goes back to the Indo-European “sli”, which means “bluish”. And of course you have to think of Slivovitz, the Czech or Slovak plum brandy. The nickname “German Acacia” was probably also created because the very hard wood was used for whips and canes, which further extends the colourful collection of blackthorn names.

Large-fruited Blackthorn Reto

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Picture: Blackthorn 'Reto' Prunus spinosa - the blackthorn with the mild aroma and the early ripening period

The large-fruited blackthorn Reto is characterised mainly by its early ripening period and mild aroma. In contrast to the wild blackthorn and other cultivars, it reliably matures even before the first frosts in September/October. The maturity is indicated by the uniform, blue skin up to the stem. The blackthorn can then be enjoyed well when fresh, if you love the blackthorn aroma with the bitter, almond-like flavour. Otherwise, the most diverse processing options such as purees, jams, making brandy, liqueurs and distilling are possible. And as I said, with the variety Reto you do not have to wait until after the impact of the first frost that makes the fruits of other varieties and the wild species ripe for consumption and ready for processing.

Short description of the large-sized blackthorn Reto

Flowers: As early as the 2nd year, all of the shoots are richly covered with white flowers (including the attractive, yellow stamens); it blooms before the leaves sprout in March and April
Harvest: High yields, especially if a pollinator variety is present; the blackthorn Reto can be harvested even before the frosts because in this cultivar the acid and bitterness are degraded earlier – already in September and October. In contrast to the wild plants, Reto does not have to wait until after the frost for the harvest to start. The ripeness of the fruits can be seen when the deep blue fruit colour is evenly pronounced up to the stem
Pollination: Only partially self-fertile; for a rich harvest, a second other type of blackthorn must be planted; the pollination by a plum or damson that is up to 30 - 50 m away usually works
Fruits: Large, 1.5 - 2 cm in diameter, twice as big as the wild fruits, high vitamin C content
Growth: Rather sparse, about 250 - 300 cm; only a few thorns in contrast to the wild blackthorn

Large-fruited Blackthorn Godenhaus

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Picture: Blackthorn Godenhaus Prunus spinosa – a blackthorn with strong, healthy growth and large fruits

The blackthorn variety Godenhaus was selected by Gartenbau Ahrweiler, namely from natural resources near Trier, Germany. Of all known cultivars it is probably the one with the largest fruits (approx. 2 cm in diameter) and it also has the highest yield overall. The crown volume is also larger; Godenhaus grows about 3-4 m high, rather sparse and begins to bear fruit in the 2nd or 3rd year. Here our strong, already 2-year-old plants help to accelerate the yield. The early ripening period is not quite as pronounced as with the variety Reto, so with Godenhaus it is worthwhile to wait with the harvest until the first frosts. But then you will be rewarded with the longed-for, intense, tart-sour-sweet blackthorn aroma, which is especially good for making juice, jam, liqueur or brandy.

Short description of the large-fruited blackthorn Godenhaus

Flowers: White, dense inflorescences
Pollination: Although the variety Godenhaus seems to be slightly better developed than other varieties concerning the self-fertility, we recommend planting of a second type of blackthorn. Alternatively, the blackthorn may also be planted near a plum or damson variety (up to 30/50 m apart) in order to ensure cross pollination.
Harvest: October - November, even possible before freezing, but it is better to wait for the first frosts. If you harvest too soon and the fruit is still too bitter and too sour, you can freeze it first – and then thaw it for processing. This has the same effect as the frost on the tree: acid and bitterness are broken down
Fruits: Large, up to 2 cm, the largest yield of all cultivars (but also has a larger crown volume)
Growth: Sparse, strong growth, slightly taller, 3 - 4 m

Large-fruited Blackthorn Nittel

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Picture: Blackthorn 'Nittel' Prunus spinosa – the blackthorn with the compact growth

The large-sized blackthorn Nittel was also selected by Gartenbau Ahrweiler from natural resources near Trier, Germany. In contrast to the other Ahrweiler selection Godenhaus, Nittel is compact and very densely branched and is no higher than 250 cm, making it perfect for a smaller garden. The fruits are significantly larger than the wild form (17 mm on average) and they should be harvested after the first frosts. Then the greatest acidity and bitterness are broken down and the fine blackthorn aroma emerges (reminiscent of bitter almonds). Tests have shown that the variety Nittel is also very well suited for making schnapps and it preserves its aroma there as well.

Short description of the large-fruited blackthorn Nittel

Flowers: Dense, white flowers, from the 2nd year. The yellow stamens are also always attractive, which make the white of the petals shine even more
Harvest: Nittel is more of a late maturing variety, so it should be harvested after the first frosts in order to make the fruits even milder
Fruits: Large-fruited, about twice the size of the wild blackthorn, average diameter: 17 mm
Growth: Compact, bushy, well-branched habit, 2-2.5 m; in contrast to the wild blackthorn shrubs, the branches of this cultivar only have a few thorns. The rather small leaves are attractive

 
 
 
 

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