Moss rose (Portulaca grandiflora) is an unfussy plant that thrives in hot, dry conditions, and you can grow it from seed outdoors, or start it indoors. Moss rose is an annual plant, which means it flowers, sets seed and dies within one growing season. It grows 4 to 8 inches tall and 6 to 24 inches wide, and flower colors include white, yellow, pink, orange and purple, depending on the variety.
When to Sow
Moss rose seeds sprout best when it's warm. In areas that experience frosts, sow rose moss seeds outdoors after the average final frost date, or sow them indoors six to eight weeks before this date. In warm climates that experience no frosts, sow rose moss seeds any time in spring. Rose moss seeds sprout when temperatures are between 70 and 85 degrees Fahrenheit.
Rose moss tolerates poor, sandy and gravelly soil, but grows best and produces the most flowers in rich, moist, well-draining soil.
Prepare the Area
Rose moss seeds are extremely tiny, and benefit from a well-prepared seed bed, or fine potting soil formulated for growing seedlings. Break up the soil in an outdoor sowing site in full sun, to a depth of 6 inches with a garden fork. Remove stones, roots and other debris, and rake the soil until it resembles fine breadcrumbs.
To sow moss rose indoors, use plant pots that are 4 inches wide and have drainage holes. Fill the pots with a potting compost for seeds. Lightly firm the potting soil surface with a piece of wood or the heel of your hand.
How to Sow
Mixing moss rose seeds with an equal quantity of dry horticultural sand helps prevent the seeds from clumping together. Sprinkle the sand and seed mixture finely and evenly over an outdoor bed on a dry, still day, or sprinkle the mixture over the surface of potting soil in containers indoors. Don't cover moss rose seeds because they need light to sprout.
Water the seeds with a watering can that has a very fine rose -- the holes in the spout -- to avoid washing the seeds away. You can also use the "mister" setting on a hose. Another option is for moss rose seeds sown in containers is to stand them in water that reaches halfway up the container sides. When the potting soil surface is moist, remove the containers from the water and allow them to drain thoroughly. Moss rose seeds usually sprout in 10 to 14 days.
Thinning moss rose seedlings encourages them to grow into healthy plants. When moss rose seedlings have developed their second set of leaves, gently pull out some of the weaker seedlings to space those that remain about 3 inches apart. Pull out moss rose seedlings in containers so that three evenly spaced plants remain in each container.
Transplant moss rose seedlings in containers into the garden when the plants are about 2 inches tall and the average last frost date has passed. Place the plants outdoors during the day and bring them inside at night for one week before transplanting them into the garden. Prepare the growing site by loosening the soil to a depth of 6 inches with a garden fork, and plant the moss rose seedlings in a hole the same size as their containers, at the same growing depth. Water moss rose seedlings when the soil surface is dry.
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