Overview
Trifolium dubium is a small, slender annual in the pea family, with sprawling to weakly upright stems 4-12 inches (10-30 cm) long. The leaves are clover-like, divided into three small, finely toothed leaflets, the central one on a tiny stalk. From late spring through summer it bears compact rounded flower heads about 0.2-0.3 inch (5-9 mm) wide, each holding 5-20 small yellow pea flowers that turn pale brown and papery as they age and hang down over the developing seed. The plant fixes nitrogen through its root nodules and is one of several small clovers sold or claimed as the true shamrock. Trifolium dubium self-seeds and grows quickly in lawns, meadows, roadsides, and waste ground, often where soil is thin and low in nitrogen. It tolerates mowing and poor soil but is short-lived, dying after it sets seed. In lawns it can spread into patches, though it also adds nitrogen and forage value. Its small size and pale, fading flower heads make it easy to overlook among grasses.
Native Range
Trifolium dubium is native to Europe and western Asia. It has naturalized widely in North America, Australia, and other temperate regions, growing in lawns, pastures, meadows, roadsides, and disturbed open ground.Suggested Uses
Grown in some lawn seed mixes, meadows, and pasture blends as a low nitrogen-fixing legume and minor forage plant. It is also sold as a shamrock around St. Patrick's Day, one of several clovers given that name. In gardens it is more often a self-sown weed of thin turf than a deliberate planting.How to Identify
Appearance
Size & Dimensions
Height4" - 1'
Width/Spread6" - 1'
Bloom Information
Flowering runs from late spring through summer, roughly May to September, with many small heads opening over the season. Each yellow head fades to brown as the seeds ripen beneath the dried petals. Small bees and other insects visit, though the plant also self-pollinates.
Detailed Descriptions
Foliage Description
greenGrowing Conditions
Sun Requirements
Requires 5-12 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Water & Climate
Water Needs
Care & Maintenance
Care Guide
Trifolium dubium grows in full sun to light shade on poor to moderate soils across a pH of about 5.5-7.5 and favors thin, low-nitrogen ground where grasses are sparse. As a nitrogen-fixing annual it needs no feeding and improves soil fertility as it grows. It germinates in cool, moist conditions, flowers and seeds in one season, then dies. In lawns it is left in place for its nitrogen and forage value or removed by improving turf density and fertility, which crowds it out. It is hardy as a cool-season annual across USDA zones 4-9. It has few pests of note.Pruning
No pruning is practiced. In lawns it is simply mown with the grass, which it tolerates well. Where unwanted, plants are removed before the heads set seed to limit spread.✓ Toxicity
Non-toxicPlanting Guide
Planting Methods & Timing
Planting Method
direct sow
Direct Sow Timing
cool soil in spring
Days to Maturity
60–90 days
Plant Spacing
4 inches