Subterranean clover (Trifolium subterraneum), commonly known as “sub clover,” is a leguminous plant native to the Mediterranean but widely cultivated in Australia. It’s especially popular in pastures and as a cover crop in gardens due to its nitrogen-fixing ability, which improves soil fertility.

Uses in the Garden

• Nitrogen Fixation: Sub clover has the ability to fix atmospheric nitrogen into the soil, making it an excellent green manure. This reduces the need for synthetic fertilisers and helps improve soil structure.
• Ground Cover: It provides a dense mat of foliage, suppressing weeds and helping to reduce soil erosion.
• Mulch and Organic Matter: As it dies back, it adds organic matter to the soil, enriching it for future plantings.
• Attracts Beneficial Insects: Sub clover flowers are attractive to pollinators like bees, contributing to a healthy garden ecosystem.

How to Grow Subterranean Clover from Seed

1. Planting Time

• Best Time: Autumn (March to May in Australia), as sub clover prefers to establish before winter and thrives in the cooler months.
• Soil Temperature: Ensure soil temperatures are around 10-20°C for optimal germination.

3. Seed Preparation

• Scarification: Sub clover seeds can have hard coats, so scarification (lightly scratching the seed coat) may improve germination rates.

4. Site Preparation

• Soil Type: Sub clover grows best in well-drained, loamy soils but can tolerate a range of soil types as long as water logging is avoided.
• pH Range: Aim for a soil pH between 5.5 and 7.0.
• Weed Control: Clear the planting area of weeds to give the sub clover a good start.

5. Sowing the Seeds

• Depth: Sub clover seeds should be planted no deeper than 1-2 cm to ensure good germination.
• Spacing: If planting for garden ground cover, broadcast the seeds evenly over the soil or plant them in rows with 5-10 cm between plants.

6. Watering

• Initial Watering: Keep the soil moist after sowing to encourage germination.
• Ongoing Watering: Sub clover is relatively drought-tolerant once established, but young plants benefit from regular watering during dry spells.

7. Maintenance

• Mowing/Grazing: Sub clover responds well to mowing or light grazing if used in a pasture setting. In gardens, trimming it back can encourage denser growth.
• Fertilisation: As a legume, it doesn’t require much nitrogen fertiliser. However, adding phosphorus or potassium may boost growth in poorer soils.

8. Harvesting/Dieback

• Life Cycle: Sub clover is an annual, so it will die back after flowering and setting seed, usually in late spring or early summer. Its seeds remain dormant in the soil and will germinate again in the next autumn.

By following these steps, you can grow subterranean clover successfully in your garden, improving soil fertility, controlling weeds, and supporting a sustainable growing environment!

PICTURE BY Harry Rose from South West Rocks, Australia, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons