As a gardening and landscaping expert, I can confidently say that coleus seeds do not require cold stratification. This means that there is no need to subject the seeds to a period of cold temperatures in order to speed up germination. Unlike some other plant species, coleus is a tropical native and does not have a natural requirement for cold stratification.
To ensure the best chances of successful germination, I would recommend using the freshest coleus seeds available. Fresh seeds tend to have higher viability and germination rates compared to older seeds. It’s always a good idea to purchase seeds from a reputable source or harvest them from healthy and mature coleus plants in your garden.
When it comes to sowing coleus seeds, I suggest planting 3 to 4 seeds in each pot or cell. This provides a higher chance of at least one seed germinating and growing into a healthy plant. It’s also a good idea to lightly cover the seeds with a thin layer of soil, about 1/8 to 1/4 inch deep, to help maintain moisture and provide some protection.
In terms of timing, it’s best to start your coleus seeds indoors at least 8 weeks before your last frost date. This allows sufficient time for the seeds to germinate and grow into sturdy seedlings before they can be transplanted outdoors. Coleus is a warm-season annual, and starting the seeds indoors gives them a head start in establishing a strong root system and foliage.
During the germination process, it’s important to keep the soil consistently moist but not waterlogged. Providing bottom heat, such as using a heat mat, can also help speed up germination. Aim for a temperature range of around 70 to 75 degrees Fahrenheit, which is ideal for coleus seed germination.
Once the seedlings have developed a few sets of true leaves and the risk of frost has passed, they can be gradually acclimated to outdoor conditions and transplanted into their permanent locations in the garden or containers. Coleus plants thrive in partial shade to full sun, depending on the variety, and they appreciate well-draining soil and regular watering.
Cold stratification is not necessary nor recommended for coleus seeds. By using fresh seeds, sowing multiple seeds per pot, and starting them indoors 8 weeks before the last frost, you can increase the chances of successful germination and grow healthy coleus plants in your garden.
