Understanding Oxalis Bulbs
Planting oxalis bulbs is a rewarding endeavour, bringing delicate, clover-like foliage and often vibrant flowers to gardens and containers. These small tubers, often referred to as sorrel, are prized for their ease of growth and striking visual appeal. Understanding their natural cycles is key to successful oxalis bulb planting.
Oxalis species vary, but most commonly cultivated varieties are dormant during certain periods, typically summer or winter, depending on the specific type and climate. Knowing whether you have a summer-dormant or winter-dormant variety will dictate the prime planting times. For instance, many popular varieties native to South Africa, like Oxalis triangularis, go dormant in summer heat and are best planted in autumn or spring. Conversely, those with woodland origins might prefer spring planting after the last frost.
The term 'oxalis bulbs' can be slightly misleading, as they are technically corms or rhizomes. Regardless of the precise botanical term, they are the underground storage organs from which new plants emerge. Their small size and potential for rapid multiplication make them ideal for naturalising in suitable climates or for creating dynamic displays in pots.
Many gardeners confuse oxalis with common weeds, particularly the small, yellow-flowered varieties often found in lawns. While some wild oxalis species are indeed considered garden nuisances, the cultivated ornamental types, with their diverse leaf colours and flower forms, are highly sought after. Distinguishing between ornamental types and common weeds like *Oxalis corniculata* (creeping oxalis) or *Oxalis pes-caprae* (Bermuda buttercup) is important, though the planting principles for the ornamental corms remain similar.
The success of your oxalis bulb planting hinges on selecting healthy tubers and providing the correct conditions. Look for firm, plump corms free from mould or damage. If they appear dry, a brief soak in lukewarm water for a few hours can help rehydrate them before planting.
Healthy tubers are the foundation of a successful planting.
When to Plant Oxalis Bulbs
Timing your oxalis bulb planting is crucial for encouraging robust growth and abundant flowering. The optimal window depends heavily on your local climate and the specific oxalis variety you are cultivating. Generally, these plants thrive when planted during their natural growing season and allowed to establish before extreme weather conditions, whether hot or cold.
For most common ornamental oxalis species grown in temperate climates, including popular varieties like *Oxalis triangularis* (often called false shamrock), the ideal planting times are spring and autumn. Spring planting, after the risk of hard frost has passed, allows the bulbs to establish in warming soil before the summer heat. Autumn planting, typically from late summer through to early autumn, gives the bulbs time to root before winter dormancy sets in, or before the onset of cooler weather if they are winter-growing varieties.
Spring Planting Considerations
Planting in spring is generally the safest bet for beginners. It aligns with the start of the main growing season for many plants. If you live in an area with mild winters and your oxalis variety is suited to it, you can plant from early spring onwards. Ensure the soil temperature is consistently above 7°C (45°F). This period allows them to grow and flower through the spring and early summer. If your variety is summer-dormant, they will likely put on a good show before entering their resting phase.
Autumn Planting Benefits
For varieties that prefer cooler conditions or for those living in warmer climates where summers are intense, autumn planting can be more advantageous. Planting in autumn means the bulbs develop a strong root system over the cooler, moister months, preparing them for vigorous growth when spring arrives. In regions with mild winters, some oxalis varieties will even grow and flower through the winter. Aim to plant from late August through to October in the Northern Hemisphere, or March to May in the Southern Hemisphere.
The right season allows oxalis corms to establish before facing environmental extremes.
If you're unsure about your specific variety's dormancy cycle, planting in both spring and autumn can sometimes yield success, as you might catch a favourable growth period. Observing when dormant bulbs appear in established clumps in gardens can also offer clues. If you notice leaves dying back in summer, it's a strong indicator of a summer-dormant type that prefers autumn planting. Conversely, if they die back in winter, spring planting is generally preferred.
Prevent disappointment by checking the origin of your oxalis corms; varieties from warmer climates may perform best with autumn planting even in cooler regions, provided they have adequate winter protection.
How to Plant Oxalis Bulbs
Successfully planting oxalis bulbs requires attention to detail regarding depth, spacing, and soil preparation. While these plants are known for their resilience, providing them with the right start significantly improves their chances of flourishing and producing their characteristic foliage and blooms. The process is straightforward, whether you are planting in the ground or in containers.
Preparing the Soil
Oxalis corms prefer well-draining soil. They detest sitting in waterlogged conditions, which can lead to rot. For garden beds, incorporate plenty of organic matter like compost to improve drainage and fertility. If planting in pots, use a good quality potting mix that is formulated for containers, ensuring it offers aeration. Adding a small amount of perlite or grit can further enhance drainage.
Planting Depth and Spacing
The general rule for planting bulbs is to plant them at a depth roughly two to three times the height of the bulb itself. For most oxalis corms, this translates to a depth of about 2-5 cm (1-2 inches). Plant them with the pointy end facing upwards, though if you're unsure, planting them on their side is usually fine as they will orient themselves correctly.
Spacing depends on the desired effect. For individual clumps, give each corm about 5-10 cm (2-4 inches) of space. If you are planting a large number for a carpet effect or naturalising, you can plant them closer together, perhaps 2-3 cm (1 inch) apart, as they will multiply over time. In containers, space them according to the pot size, ensuring they are not overcrowded, especially if you aim for them to establish and spread.
In the Ground vs. Containers
In the ground: Dig a trench or individual holes to the correct depth and spacing. Place the corms, cover them gently with soil, and water them in lightly. Choose a location that receives adequate sunlight – typically 4-6 hours per day, though some varieties tolerate partial shade. Avoid areas where water pools after rain.
Container Planting
For containers, ensure the pot has drainage holes. Fill the pot with your prepared potting mix, leaving enough space to place the corms at the correct depth. Arrange the corms on the soil surface, then cover with more potting mix. Water thoroughly after planting. Containers offer more control over soil conditions and can be moved to provide protection during extreme weather or to accommodate the plant's dormancy period.
When planting multiple oxalis varieties with different dormancy requirements, consider planting them in separate containers to manage their care cycles more effectively.
Aftercare and Maintenance
Once your oxalis bulbs are planted, providing appropriate aftercare will nurture them into healthy, blooming plants. The key to sustained success lies in understanding their seasonal needs, particularly their dormancy periods and watering requirements.
Watering Needs
Water your newly planted oxalis corms gently but thoroughly to settle the soil around them. During the active growing season, keep the soil consistently moist but not waterlogged. Check the soil moisture regularly, especially for container-grown plants, as they can dry out more quickly. When the plant begins to show signs of dormancy, usually indicated by yellowing or dying foliage, reduce watering significantly.
Dormancy Management
Managing the dormant period is critical for the long-term health and prolific blooming of your oxalis. For summer-dormant varieties, once the foliage has died back, cease watering and allow the soil to dry out. You can leave the corms in the pot or in the ground. If in pots, store them in a cool, dry place, away from direct sunlight, until you are ready to water them into growth again, typically in autumn or early spring. For winter-dormant types, they will naturally rest during the hottest months; continue to water sparingly during this time if growth appears to slow, then resume normal watering as temperatures cool and growth restarts.
Respecting dormancy cycles is as important as correct planting.
Feeding Your Oxalis
Oxalis plants are not heavy feeders. Generally, incorporating good quality compost into the soil at planting time is sufficient for most varieties. If you wish to provide additional nutrients, a diluted liquid feed can be applied during the active growing season, perhaps once a month. Avoid over-fertilising, which can lead to excessive foliage growth at the expense of flowers or can damage the delicate corms.
Dealing with Pests and Diseases
Oxalis is relatively trouble-free, but like all plants, it can be susceptible to issues. The most common problem is rot, caused by overwatering and poor drainage. Ensure good airflow and do not let pots or beds become waterlogged. Aphids can occasionally infest the foliage, especially in sheltered conditions. A strong jet of water or an insecticidal soap solution can usually manage minor infestations.
The small, often yellow, weed-like varieties of oxalis can be challenging to eradicate if they establish themselves in garden beds or lawns. However, ornamental oxalis grown intentionally are generally less problematic. Keep an eye out for any signs of distress and address them promptly through appropriate watering, feeding, or pest control measures.
Alternative Approaches to Oxalis Cultivation
While traditional planting of oxalis bulbs in soil is the most common method, several alternative approaches can yield beautiful results, particularly for specific environments or aesthetic goals. These methods often leverage the plant's vigour and adaptability.
Growing in Water (Hydroculture)
Some oxalis varieties, particularly *Oxalis triangularis*, can be grown hydroponically or in water. This method bypasses soil altogether, allowing the corms to sprout directly in water. Place the corms in a decorative vase or container, ensuring the base of the corms just touches the water or a very small amount of water is present. As roots develop, they will extend into the water. This technique requires regular water changes to prevent stagnation and needs a bright location. It offers a unique, modern aesthetic, making the root structure and emerging foliage the focal point.
Terrarium Planting
Creating a terrarium with oxalis can result in a miniature, self-contained ecosystem. The enclosed environment provides consistent humidity, which many oxalis varieties appreciate. Use a well-draining substrate mix, and plant the corms as you would in a pot. Choose a terrarium that allows adequate light penetration. Monitor moisture levels carefully, as enclosed spaces can retain water, potentially leading to rot. This is an excellent way to showcase the intricate foliage, especially with cultivars like *Oxalis triangularis 'Atropurpurea'*.
Naturalising in Shady Areas
In suitable climates, oxalis can be naturalised in woodland gardens or beneath deciduous trees. The dappled shade mimics their natural habitat and can provide a cooling effect during warmer months, potentially extending their active growth period. Plant them in drifts, allowing them to spread and fill in over time. Ensure the soil is moist and well-draining. Be mindful that if they are indeed spreading like a weed, they can become difficult to manage, so choose the location carefully.
Forcing for Indoor Blooms
Oxalis bulbs can be 'forced' to bloom indoors, often timed for winter displays. This involves planting them in pots filled with potting mix, keeping them cool and relatively dry for a few weeks to encourage root formation, and then moving them into a bright, warmer location. Watering them into growth will prompt them to sprout and flower, providing a welcome splash of colour when outdoor gardening is limited. Use a mix of corms to ensure a succession of blooms.
Experimentation with containers and environments can unlock new visual possibilities.
For a striking indoor display, plant oxalis corms closely in a shallow dish or pot, mimicking a carpet of foliage and flowers that will emerge relatively quickly under indoor light and warmth.