While some grow it intentionally as a groundcover in their lawn or garden, oxalis is widely regarded as a weed. This small, clover-like plant can take over a lawn or garden quickly and is notoriously challenging to get rid of. However, there are some measures you can take toward the control and management of oxalis weeds.
To get rid of oxalis, you can either pull it by hand or treat it with a weed killer containing glyphosate. In lawns, you should follow up the removal of this weed with sufficient maintenance including proper fertilization, watering, and mowing to prevent oxalis from returning.
What is Oxalis?
Oxalis, also known as buttercup oxalis, wood sorrel, or sourgrass, is a low-growing perennial weed found in lawns around the world. Looking similar to clover, some actually grow oxalis intentionally in gardens to act as a groundcover crop. However, to most, oxalis is an irritating invasive weed that is notoriously challenging to get rid of.
The reason why oxalis is such a persistent weed is due to the way in which it spreads. This weed spreads through interlocking rhizomes that break apart easily in the soil. Each rhizome that oxalis produces eventually produces its own bulbils; these are bulb-like structures that allow the weed to grow and spread through the soil. Oxalis can also spread prolifically through seed pods that eject tiny seeds when ripe.
In terms of the plant’s structure, oxalis grows a long, fleshy taproot and an extensive root system that branches through the soil. Basically, oxalis is able to root anywhere that its stem touches the soil. It is due to this extensive root system and its spreading capabilities that make oxalis such a challenging weed to manage.
Where Does Oxalis Grow?
Oxalis grows well under a range of conditions. It thrives in moist, poorly draining, fertile soil, growing where it has full access to the sun. At the same time, oxalis can also grow well in shaded or dry conditions. It can grow sporadically among shrubs and flowers in landscape beds or in vegetable gardens. It also invades lawns, particularly those that are undernourished or have bare spots.
Oxalis Weed Identification
Oxalis appears very similar to clover, another common invasive weed. They have hairy upright stems that prop up 3 heart-shaped leaves. When oxalis flowers, it produces flowers with 5 yellow petals that grow singly or in clusters on the weed’s stalks. The plants can grow to be 4 to 12 inches tall.
How to Get Rid of Oxalis
The two methods available to get rid of oxalis include removing it by hand or killing the oxalis with a weed killer.
1. Pull Oxalis By Hand
The first method to get rid of oxalis in a lawn or garden bed is to pull it up by hand. While this method is unsuitable for larger infestations, you can effectively tackle smaller amounts of immature oxalis manually. The key with this method is to ensure that you remove as much of the weed from the soil as possible; leaving any portion of the oxalis in the soil, like its roots or rhizomes, means it will likely resprout.
Method: Handpick or dig up any oxalis weeds you spot before they get a chance to flower or form seeds. It’s crucial to take care to remove all vegetative parts of the weed, including its taproot, root system, and rhizomes.
Dispose of the weed’s vegetation and seeds properly and avoid placing the matter in a compost pile or bin; you may inadvertently introduce the weed back into your lawn when you later use the compost. Follow up the removal with the addition of a layer of mulch to block sunlight from reaching any remaining oxalis seeds or seedlings.
2. Kill Oxalis with a Weed Killer
The alternative method to get rid of oxalis weeds is to treat them with a chemical weed killer. This is a suitable approach for both small and larger infestations of oxalis in lawns or garden beds.
2.1 Killing Oxalis in a Garden Bed
If removing oxalis in a garden bed, you can spot treat the individual plants using a non-selective weed killer containing glyphosate. This method is most effective on seedlings and immature oxalis plants that are yet to flower.
Douse the oxalis with the glyphosate weedkiller until the foliage of the weeds is thoroughly wet. Take care with your application as non-selective weed killers will kill any other vegetation they make contact with. Always read the safety and application instructions on the label of your chosen product before using it around your plants; some products aren’t safe for use around landscape ornamentals and established perennial plants.
2.2 Killing Small Infestations of Oxalis on Lawn
If removing a small infestation of oxalis on a lawn, use a lawn-safe weed killer. Check the label of the product to ensure it’s safe to use on your specific grass type and follow the product’s application instructions carefully.
2.3 Killing Large Infestations of Oxalis on Lawn
For larger infestations of oxalis on a lawn, it’s better to use a lawn-safe weed killer that’s designed for broadcast application. This will allow you to cover larger areas with the weedkiller using little effort. Again, make sure to follow the safety and application instructions for your product and ensure it is safe to use on your grass type.
How to Prevent Oxalis in Lawns
You can prevent the growth of weeds such as oxalis by keeping up with your regular lawn care activities throughout the year. This involves following proper fertilization, mowing, and watering schedules to maintain the health of your grass and its root systems.
Fertilize Lawn Regularly
Keeping your lawn well-fertilized is an important practice to choke out the growth of invasive weeds such as oxalis. By adding fertilizer, you’re giving your grass plants a hearty dose of nutrients like nitrogen, phosphorus, and potassium; these are the primary nutrients that all plants need to grow strong foliage and extensive root systems.
When your grass plants have an abundant supply of these nutrients, it ensures the thick, healthy growth of your lawn. The thicker foliage provides the soil surface with more shade from the sun; in turn, this prevents sunlight from reaching weed seeds and young weed seedlings, reducing the establishment of new weeds. The grass’ extensive root system crowds the soil, leaving less space for weeds to establish their own roots.
Method: To prevent the growth of oxalis weeds, you should fertilize your lawn 2 to 4 times throughout the growing season. To give a general idea of how often to fertilize, the first fertilization should be in early spring; the second in late spring; the third during summer; and the fourth in fall. Avoid fertilizing your lawn any more than this, as too much nitrogen from overfertilization can cause your grass to turn yellow or brown due to a condition called fertilizer burn.
The best type of fertilizer to use on a lawn is generally said to be a slow-release, organic fertilizer. However, if you’re trying to prevent weeds such as oxalis, you may wish to use a fertilizer product containing a pre-emergent weed killer. These fertilizers enrich your lawn with nutrients at the same time as preventing the germination of new weed seeds. Before fertilizing, test your lawn to find out its pH and nutrient content; you can then use this information to choose the best fertilizer for your grass’ specific needs.
Mow Lawn Higher
Another method to promote a healthy lawn free of weeds like oxalis is to mow the grass as high as possible. When you cut the lawn too short, it causes the grass to grow shorter, weaker roots, resulting in a weaker lawn overall. Mowing the grass longer instead encourages the grass to grow deeper, more extensive root systems to support the taller grass blades. This leaves weeds like oxalis with less space in the soil to develop their own roots.
Also, as we’ve just mentioned, taller grass blades help shade the soil surface from the sun. This prevents new weeds from establishing themselves and helps to choke out those that are already established. It also reduces the amount of water lost to evaporation, reducing the amount of water you need to add through irrigation. On top of all of this, longer grass helps to prevent the development of other lawn issues such as fungal disease or pest infestations.
Method: Mow your lawn following a regular mowing schedule, mowing the ideal height for your grass type. All grasses have their own recommended mowing heights; find out the best height range to cut your specific grass type, then set your mower deck to mow at the tallest height within that range.
To give a general idea of the best heights for some common grass types, mow fescues, perennial ryegrass, Kentucky bluegrass, and St. Augustine lawns to 3 to 4 inches; centipede grass and Zoysia grass lawns to 2 to 3 inches; and bermudagrass lawns at 1.5 to 2 inches. As an additional tip, leave the grass clippings on the lawn to act as a natural grass clipping compost, or bag the clippings to use for other purposes around your home.
Water Lawn More Deeply
The third way to encourage the thick and healthy growth of your lawn and choke out weeds is to water it less frequently, but add more water each time. Watering regularly while adding little water causes the grass plants to grow shorter, shallow roots. This results in a thin lawn filled with bare spots, leaving room for invasive weeds like oxalis to move in.
Method: Water your lawn one to two times per week, doing so enough to add 1 to 1.5 inches of water. Rely on the rain as much as possible to add this water, topping it up with irrigation when necessary to reach the 1 inch per week mark.