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The horned wood-sorrel, which belongs to the botanical genus Oxalis, is a real nuisance in the garden, because the robust and prolific species likes to colonize garden beds, lawns and pavement joints. Once established, you won't get rid of Oxalis corniculata that easily. The weed thrives almost everywhere and spreads again and again both through its numerous seeds and the deep roots. With these means you finally fight sorrel.
wood sorrel
You can easily recognize the horned wood-sorrel by its dark green to red-brown leaves, which are perfectly adapted to strong sunlight due to their dark colour. Between June and October, the bright yellow flowers appear incessantly, which soon turn into capsule fruits up to two centimeters long. These in turn contain numerous small, brown seeds.
Basically, wood sorrel grows on almost any surface, so it is quite undemanding in terms of soil composition and location. However, the weeds feel most comfortable on soils with these characteristics:
- nutritious
- humorous
- slightly acidic to neutral pH
- little moist to dry
In the garden, the plant is mainly found in lawns, where it threatens to quickly crowd out the less robust grasses. But perennial beds, plant pots and stone joints are not immune to colonization either.
notice: Some weeds in the garden can be used in the kitchen and practically "eat away". Not so the horn sorrel: This contains high proportions of toxic oxalic acid and is therefore not suitable for consumption.
The weed is extremely stubborn and difficult to destroy, especially since the species reproduces extensively both by root suckers and by seeds. The narrow capsule fruits jump open at the slightest touch and throw the seeds inside several meters away - for this reason the species is also called "spring clover". Small animals such as ants do the rest and distribute the seeds in the wider area. More problematic than the seeds, however, are the stolons that sprout from the roots, which are deeply anchored in the ground. Since these can hardly be removed, especially in loamy soil, the herb keeps coming back with only superficial treatment.
Fight sorrel
If you want to successfully combat and finally destroy the horn sorrel, you have to start as early as possible: the longer you let the weeds grow rampant in your garden, the harder it is to get rid of them. Without any physical exertion, you have also lost immediately, because only through regular and thorough weeding will you assert yourself over time.
In joints
Since Oxalis corniculata keeps growing from even the smallest pieces of root, the frequently practiced flaming of overgrown stone joints is only a short-term solution. It is better to use a joint scraper to thoroughly remove the weeds and as many root parts as possible from the joints and then seal them. Close the gaps between slabs and stones as follows and you won't have any more problems with stubborn weeds:
- Thoroughly scrape joints
- fill in new, clean sand
- Sweep area and distribute sand evenly in open areas
- if necessary, cover stones
- Spray on joint strengthener
- optionally use liquid resin
On the other hand, it is easier not to let the weeds develop in the first place. For this purpose, you should already be involved when laying out the terrace or the paved path weed fleece place under the stones. Horn sorrel cannot penetrate through this, at least with its roots.
In the lawn
On the other hand, sour clover in the lawn is much more complicated to combat. The use of herbicides is out of the question here, after all, the agents make no difference between the desired grass and the weeds that are being controlled. Instead, you switch to other methods that are essentially intended to make life difficult for wood sorrel. Be patient, because the plants cannot be completely removed with a single weed. Therefore, start as early as possible in the year - ideally as early as March or April - and check the lawn at short, regular intervals for new shoots, which you can also remove immediately. It is important not to let the plants flower in the first place.
mowing
After all, if it doesn't flower, it can't produce seeds either. For this reason, mow the lawn regularly to hinder the growth of the horn sorrel. However, since the species grows very flat on the ground, you should set the lawn mower as low as possible. Between April and October, walk the entire lawn about twice a week and keep it as short as possible continuously. The frequent cutting off of the above-ground parts of the plant weakens the weeds in the long term, so that they gradually recede.
liming
Regular liming of the lawn can also help against horn sorrel - but does not have to. After all, the weeds also thrive on slightly calcareous substrates and cannot be driven away with mere liming. Nevertheless, this measure is to be rated positively, because it strengthens the growth and defenses of the grass - and Oxalis finds fewer opportunities for unhindered spread.
tip: However, do not just loosen lime, but first check by means of a soil analysis whether there is a corresponding need at all. Contrary to some claims, the horn sorrel is by no means an indicator plant for soil that is too acidic.
Fertilize
The right fertilization is often more effective against wood sorrel than liming the lawn: Since weeds prefer to grow on nutrient-poor substrates and only have a low nitrogen requirement, you can prevent them from spreading or even destroy them with regular lawn fertilization. Horn meal, which is a purely organic fertilizer, is perfect for this purpose. Horn meal only supplies the soil with nitrogen, but decomposes only very slowly and thus counteracts over-fertilization.
tip: Be careful with fertilizers with a high phosphate content. Horn sorrel needs phosphorus above all for its growth and reacts accordingly happily to an appropriate supply.
Replace lawn
A massive spread of wood sorrel on the lawn can only be combated in the long term by one measure. Destroy the weeds with a thorough renewal of the entire lawn. The best way to do this is as follows:
- Fertilize the lawn vigorously
- Let grow for 14 days, do not mow
- then cut as low as possible
- scarify the area
- Remove areas densely overgrown with wood sorrel
- apply fresh topsoil
- Reseed the lawn
- Thoroughly water the area
You can remove only partially strong weed growth in the same way, except that in this case you do not have to treat the entire lawn. Remove the sorrel with the help of a digging fork. Remove the top layers of soil (and thus remove any root remains) and sow new lawn or cover the bare spots with turf.
vinegar and pelargonic acid
Instead of using toxic herbicides, you can also combat sorrel growth by spraying leaves that appear between stone joints with undiluted vinegar. However, the treatment only has a superficial effect and the plants repeatedly sprout from the roots. Vinegar, on the other hand, is not suitable for lawns, as the agent also attacks the grass. The natural fatty acid pelargonic acid, on the other hand, is completely unsuitable for weed control because it breaks down very slowly and also easily gets into water.
Prevent
Prevent a horn sorrel invasion with careful and regular lawn care: mowing, scarifying, liming, fertilizing and watering during the summer months help to ensure that the green area remains healthy and that only the desired grass grows in it. In addition, before planting within the lawn area, you should thoroughly examine newly purchased container plants for any oxalis and other weeds that may occur and remove them if necessary. Weeds are often introduced from the outside, but with proper control you can avoid this.