The Blackthorn fruit tree produces surprising fruits, sloes, that are always best when they’ve burst just after the first frost spells.
Blackthorn basic facts
Name – Prunus spinosa
Family – Rosaceae
Type – shrub
Height – 3 to 16 feet (1 to 5 m)
Growth rate – 1 to 2 feet/year (30 to 60 m)
Exposure – full sun to part shade
Flowering – March to April
Fruit – sloe, plural sloes
(a famous crossword trick), from year 3
Foliage – deciduous
Planting blackthorn
It is ideal to plant blackthorn in fall to boost root development before winter.
You can still nonetheless plant your blackthorn in spring if you’ve purchased it in a container.
- Blackthorn loves sunbathed locations to produce sloes.
- It appreciates rather rich soil.
- Poor and clayish soil isn’t its best growing environment.
- Take care, if this is the case, to water regularly at the beginning for roots to penetrate well.
Take note that blackthorn is… full of thorns, place it well so that you won’t be pricked too often when passing by!
It is thus also ideal to create a tough defensive hedge, on top of its ornamental appeal.
Care and pruning of blackthorn
Caring for blackthorn is very easy because it is a shrub that requires quasi no care once it has settled in correctly.
- Regularly water over the 1st year after planting.
- Fertilize poor soil with shrub fertilizer during the 2 or 3 first years.
Pruning blackthorn
Blackthorn is one of the faster-growing shrubs. In the first years of growth (it matures and slows after 10 to 15 years), it can grow up to 2 feet a year, with a minimum of 1 foot when conditions aren’t perfect (60 and 30 cm, respectively). Pruning, of course, reduces overall height, but makes up for it by creating a lusher, denser bush. Indeed, each cut twig will sprout from 2 to 4 new branches lower down.
If you must prune or cut back your blackthorn, avoid proceeding after the blooming, or you won’t be harvesting any fruits.
If your blackthorn turns invasive:
- Wait for fall to cut it back drastically every 2 or 3 years.
- Remove suckers sprouting from the base often during the year.
Blackthorn can cope well with severe pruning, hatracking and even being cut down to the stump.
Caution: blackthorn spikes can be over 4 inches (10 cm) long, are very sharp and very strong.
- When pruning, it’s important to wear thick gloves and especially protective glasses to protect your eyes.
- You can also snip off spikes on lower branches with pruning shears. This makes weeding underneath them easier for the season!
Harvesting sloes
Sloes appear on the tree after the first blooming, usually in the third year of growth. Only a handful make it the first year, but the following years already provide abundant harvests.
It is very easy to harvest sloes from the blackthorn but, be careful, these fruits only really have any value if harvested at exactly the right time.
Sloe is astringent and bitter and doesn’t have much culinary value if harvested too early.
- Wait for a couple fall frost spells to occur before collecting the sloes.
- The sloe must be mush, with wilted skin: this is when it is at its best.
- Harvest sloes together with medlar. Both are best when over-ripe. This is called bletting.
Keeping sloes
Sloes will keep for a short while if dried out in the sun, but best is to freeze them and thaw right before cooking.
Learn more about blackthorn
Blackthorn, also called sloe bush, is part of the large Prunus family, like the apricot tree, plum tree, almond tree, peach tree and cherry tree. It actually can be used as a graft-holder for apricot trees, plum trees and peach trees.
Birds love building nests in the tree. The sharp thorns protect eggs and hatchlings from predators such as cats.
Often used to create defensive hedges, its bountiful fruits are sometimes forgotten, which is a shame because they are delicious after they’ve frozen through.
Its early blooming is simply beautiful, covering the tree even before leaves have appeared. This gives the tree a serene, meditative bearing, much like that of a Japanese garden.
Sloes are astringent if harvested too early, but always have high vitamin C contents as well as organic acids and tannin compounds.
Sloes enter into the preparation of very many recipes for spirits, wines and jams.
Smart tip about blackthorn
During the beautiful spring blooming, you can snip a couple branches off from your blackthorn and arrange them in a large vase, the decorative impact will impress all!
CC BY-NC 2.0: Marek Michalski, Hornbeam Arts
I knew nothing about this black knot fungus. I planted roughly 12 blackthorn trees around 5 years ago and the only problem I’ve seen so far has been a severe infestation of the Japanese beetle this year. I sprayed my trees with a liquid chemical from my local hardware store and it seems to be working, fingers crossed. I use two Blackthorn Irish walking sticks due to a genetic walking disorder which came from one of my GG grandparents from Ireland. I live on the family farm in Northern Illinois and my trees seem to be doing pretty well considering some of our severe winters that we have here. I’ll have to go out today and look closely at these trees to see if I can see any fungus starting anywhere. My trees started at around 10 inches tall and are now between 3 to 4 ft tall.
Hi
I have a blackthorn tree in a large pot. It was a twig when the doctors and nurses gave it to me when my son was killed in an accident coming home from work. It has grown to around 5 & half feet now and us showing signs of its first blossoms today. My question is how long can I keep it in a pot? We plan to move counties within the next year or two and will plant it in the garden. I have been growing it since 2019.
Hello Shirley, I’m sorry for your loss. It was a nice gesture the medical staff showed you when your son passed. Having a living remembrance of your son is a beautiful token that helps lead a purposeful life.
Blackthorn is an exceptionally resilient shrub. It will survive very harsh winters, occasional droughts, and can bounce back even after severe pruning. As for growing in pots, you needn’t worry: it’s often a favorite for the art of bonsai, which is telling.
If you plan to transfer it into the ground within the next two-three years, there’s no need to change your habits as to how you care for it. You can prune it a bit so that it doesn’t grow too large to move (especially with those thorns). I like reducing the size by pruning back the longer of two branches at a junction; it helps the tree keep a natural shape. Do give it a little fertilizer, or topdress it. It’ll help restore nutrients in the pot.
I am working on a large project and had a question about the last image in this post. Is this really an image of a blackthorn in bloom? Based on the yellow-orange pollen of the snow white flowers, could this image be of a damson, apple, or hawthorn tree instead? If it actually is of a blackthorn tree, does blackthorn pollen start off as yellow-orange and then age to firebrick red? Thank you for any assistance you can give.
Hi Iverson, that’s a good question. Yes, I’m certain this picture is one of blackthorn. The pollen starts off golden yellow-orange and, if not picked by bees or shaken off, it turns darker as it dries up. Usually it falls off, though, leaving the small stalks to wither. As you noticed, the flowers on each of these plants look fairly similar and are easy to confuse.
Gaspard, thank you so much for your fast, informative reply. I truly appreciate it.
Hi there, I have a self seeded blackthorn (in clay soil) that I left to grow and is now about 10 years old. It is quite a monster. I have been cutting it back hard every three years back to keep it under control. It has a strong thick ish trunk now. My question is please, is it too late to turn it into a bush/shrub? Or something creative. I am struggling to with the thorns you see. Apologies if this is a silly question, I am not a natural gardener.
Hello Val! The only silly thing is when people don’t dare to ask – so your question is very welcome!
I understand you’re faced with quite a monster! Don’t worry because blackthorn can take severe pruning easily, especially if already 10 years old with a strong root system.
For example, you can cut back every branch by 2/3rds, leaving 1 third on the tree.
In addition, you can even cut one in three branches back to the trunk, to thin it out.
If reducing it by two thirds is still too large for what you wish, you can cut more, but then it’s best to stage the pruning in time. Staging it ensures the main trunk is still the go-to point for sap and “growing power”.
– For this you can cut every other branch back to the trunk, reducing the remaining ones by half as well,
– and a year later, cut the remaining half so that all the old branches are brought back to the trunk.
– New branches will have sprouted from the trunk in the meantime. These you can form and prune more regularly to give your shrub the size you wish.
You can hatrack blackthorn, and it’ll sprout new smaller branches around each cut. This usually doesn’t look very nice, but some like it and blackthorn can take it well.
And lastly, if you want to do away with the trunk entirely, it’s possible as well. You can simply saw the entire thing off, about 6 inches or 15 cm from the ground. New shoots will sprout, most around the stump but some randomly along the main roots. Select and care for those you wish to keep!
All this pruning and cutting is best done after the harvest in late fall, if you’re collecting the sloes. It’s ok if there are light freezes after this.
It will be hard to make perfect topiary shapes from it, though. Other shrubs like box or yew are better for that.
Thank you, you have really helped. I think I am going to go with your very last suggestion, cutting it right down to about 6 inches from the ground and start again with it. Check back with you in the new year’s spring time and let you know. Thank you again.
Sure thing!
I’ve been picking sloes in the hedgerows for about 3 years and making sloe gin. It’s very popular. I’ve just a ‘grow it’ box , for growing sloes from seed. The instructions says to place the soil and seeds (after wetting) into a plastic bag. Keep the bag at a temperature of around 18-20C for about 2 weeks. After this, place the seeds in the fridge for at least 18 weeks. If these instructions are correct, in which month is it best to begin this process so that the seedlings can be planted outside in the most suitable month?
Hello Chris! Sowing blackthorn is a long process indeed. I’m supposing the seeds have already come from dry storage, they’re in a deep dormant phase.
The best planting window being fall, say mid-September, it would make sense to start early-to-mid-May which is 20 weeks earlier.
However, it isn’t advised to plant young seedlings directly into the ground on the first winter. It’s best to wait for them to be around a year old or so before planting them to the ground. So you could start them now (since you’ve got the box) and keep them in a lean-in or unheated greenhouse over the winter before planting them in fall next year. That would be best since they would have grown a bit and would be around 8 months old upon planting to the ground.
If you’ve got spare seeds, try sowing some now directly where you plan to grow them. They’ll have their cold cycle during winter and naturally sprout in spring.
If you have lot of seeds and can accept heavy dieback (like 3/4ths dying off), you can go ahead and start the process next May and plant the seedlings to the ground directly as they sprout. Having those seedlings face the harsh winter immediately will give them “staying power” and train them to face the cold… for those that survive, of course!
I had a beautiful blackthorn hedgerow which grew for over 10yrs. However it succumbed to black knot fungus which I was completely unaware of at the time! No one told me to watch out for this and it was too late for treatment when I finally discovered what was wrong!! So upset!!
Hi Mags! Oh, my, I understand that you must really be upset! Black knot fungus is usually expected on fruit trees, and having a hedge suffer and die must have been a disappointment. Hopefully you found a new shrub to grow!
Blackthorn does well in my clay soil. The rhs entry on it corroborates this. Saying it despises clay is frankly wrong. It also tolerates fairly poor soils, half shade and is a really tough hedgerow plant.
Hi grrrrrl, thank you for your comment. The word “despise” is too strong, I’ll change it to reflect your experience. Thanks for sharing your added information about your blackthorn – always good to see someone who’s happy with this tough but fruit-bearing hedge plant!