Growing the seeds
When to plant -- Plant your seeds when you receive them for best germination
Getting started -- Use a fast-draining soil mix. A typical mix for germinating them is 1 part potting soil or coir fiber to 3 parts perlite or coarse horticultural sand. If you make your own soil mix using peat moss, add a small amount of agricultural lime (dolomite lime, not hydrated lime or quick lime) - about ½ teaspoon of lime per gallon of soil (3 cc per 4 liters).
Use small pots or cups that have drainage holes. Fill the pots, without packing down the soil. Place a seed or 2 on top and tap the side of the pot gently to settle in the seeds. Cover with a thin layer of long-fiber sphagnum moss (not ground peat moss). This helps retain moisture around the seeds while allowing light to reach them, which aids germination. This photo shows how much moss to use. If you don't have the moss, sprinkle a small amount of your potting mix around the seeds. Add water until everything is evenly moist (but not soggy).
Until the seeds sprout, ensure that the surface soil always stays moist. A propagation dome or plastic box works well for maintaining moisture. Keep the dome or box open slightly to allow fresh air in. Keep the pots in a bright spot out of direct sun. A fluorescent or LED bulb kept 4 inches (10 cm) away provides the right amount of light.
They sprout well between 68 and 80 degrees F (20-27°C). I have no experience germinating them outside that temperature range. I recommend keeping a minimum/maximum thermometer near the pots, especially if using a heating mat.
The seeds should begin sprouting in about 3 to 6 weeks, but may take up to 8 weeks to start. Increase the air ventilation slightly after they sprout to avoid rot. Continue keeping the soil surface moist for 4 weeks after they sprout, but avoid keeping the leaves wet.
Lighting -- It grows well in bright shade, dappled sunlight, or morning sun. But avoid prolonged sunlight until the plants are a few months old. It will probably need some protection from strong afternoon sun.
Transplanting -- When your plants are about 3 months old, gently transfer them to larger pots. Avoid damaging the roots when repotting. Mature plants don't need a big pot, but it should be at least 3-4 inches tall (8-10 cm).
Watering -- Try to keep the soil moist, but not soggy, most of the time. Avoid letting it dry out completely.
Climate -- Impatiens mirabilis is a tropical species that does best above 60 degrees F (15°C). It seems to be happiest between about 70 and 90 degrees F (21-32°C). I haven't grown it in cool conditions, but it probably won't grow well below 55 degrees F (13°C).
Fertilizing -- When your seedlings are 1 week old, give a small amount of diluted liquid fertilizer (about 1/4 strength), and repeat weekly. Hydroponic fertilizer is ideal for young seedlings, since it is easily absorbed and complete. After your plants are 2 months old, you may switch to an all-purpose, granular fertilizer if you wish.
Dormancy -- The plants can go dormant for a few months each year, especially if temperatures get cool. Reduce watering during this time, keeping the soil only lightly moist. Avoid letting the soil dry out completely.
Pests to watch for -- Watch for any pests that affect your other plants. Be careful when choosing chemical remedies, as some may harm the plant.
If you have any questions, feel free to email me.
Have fun growing them!
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