Spearmint (Mentha spicata) is a popular herb prized for its sweeter, milder flavor compared to other mint varieties, making it a favorite for culinary and aromatic uses. While often propagated from cuttings or root divisions, starting it from seed is an economical method for the home gardener. Successfully growing this plant requires specific attention to environmental details and a proactive strategy for managing its vigorous nature. This guide focuses on the steps to cultivate a thriving spearmint patch, from initial preparations to harvest.
Essential Pre-Planting Preparations
The timing of planting is crucial for successful germination, ideally occurring once the danger of the last spring frost has passed. For an earlier start, seeds can be sown indoors 8 to 10 weeks before the expected outdoor transplant date.
Spearmint thrives in a well-draining, moderately fertile growing medium that prevents root rot. The location should provide partial or full sun exposure. Leaves develop the most concentrated flavor when they receive brighter light. In regions with intense afternoon heat, partial shade helps prevent wilting. Before sowing, the soil should be lightly loosened and kept consistently moist.
Sowing Spearmint Seeds for Successful Germination
Spearmint seeds require light to trigger germination, so they must be surface-sown by scattering them thinly across the prepared, moistened soil surface. Avoid burying the seeds deeply; a very light dusting of soil, no more than 1/8 inch, can be used to anchor them. Gentle pressure ensures good seed-to-soil contact.
Maintaining consistent moisture throughout germination is paramount, often best achieved by misting with a spray bottle rather than using a heavy watering can that could dislodge the seeds. The ideal temperature range is 65°F to 80°F. Sprouts should emerge within seven to fifteen days. If starting seeds indoors, provide supplemental light with a grow lamp positioned a few inches above the soil surface.
Nurturing the Seedlings and Managing Spearmint Growth
Once the seedlings have developed their first set of true leaves, thinning is necessary to give the strongest plants adequate space to mature. Seedlings should be thinned to stand 12 to 16 inches apart, as overcrowding restricts airflow and nutrient availability.
Young plants started indoors should be gradually acclimated to outdoor conditions over a week or two (hardening off) before being transplanted after the last frost.
Managing Aggressive Growth
A major consideration is the plant’s aggressive, spreading nature due to its underground runners (rhizomes). To prevent colonization, spearmint is best grown in a container, such as a large pot with a minimum diameter of 10 to 12 inches. If planting directly into the ground, the plant must be contained by sinking a bottomless container or a solid root barrier 10 to 12 inches deep into the soil. The rim of this barrier must remain exposed above the soil line to prevent runners from escaping.
Harvesting Spearmint Leaves
The first harvest can commence once the spearmint plant is established and reaches a height of 6 to 8 inches, usually a couple of months after sowing the seeds. The most flavorful leaves are obtained just before the plant begins to flower, when the concentration of essential oils is highest.
Harvesting should be performed by pruning the stems, not by plucking individual leaves, as this encourages a fuller, bushier growth habit. Use clean scissors or shears to make a cut just above a leaf node. This action stimulates the plant to produce two new shoots from that node, resulting in denser foliage. Regular harvesting controls the plant’s size and ensures a continuous supply of leaves throughout the growing season.