Germinating the seeds
The seeds will germinate easily if they are fresh. Use small containers that have drainage holes, such as seedling starter trays. A well-draining soil is necessary, such as cactus soil. You may make your own mix with 1 part quality potting soil and 1 part perlite (fine- or medium-grade perlite, not coarse-grade) or coarse horticultural sand. Or use 1 part coir fiber to 2 parts perlite or coarse sand.
Fill each container, place 1 or 2 seeds on top, and sprinkle a very thin layer of soil on top - just enough to barely cover the seeds, because the seeds need light to germinate. Add water until the soil is evenly moist (but not soggy).
Until the seeds sprout, ensure that the surface soil does not dry out. If you enclose the pots in a plastic dome or bag to maintain moisture, leave it open a crack for some fresh air to enter. You may need to drip a few drops of water over them each day or 2.
The seeds germinate well between 65-77 degrees F (18-25°C) during the day (a little cooler at night is ok). I have no information about how they will sprout outside that temperature range. I suggest placing a minimum/maximum thermometer near the pots.
Keep the pots in bright light away from direct sun. A fluorescent or LED bulb kept 4 inches (10 cm) away provides the right amount of light.
Many of the seeds should sprout within 4 weeks, but allow up to 8 weeks for any slow ones. Continue keeping the surface soil moist until the seedlings have their second set of leaves - then you may let the surface dry out between waterings.
When the seedlings have their third set of leaves, you may give them some morning sun. Transition them to stronger lighting gradually, and protect them from strong sun the first 2-3 months. After about 10-12 months they should be ready for full sun.
Fertilizing -- Feed weekly with a very dilute (1/8 strength) liquid fertilizer. Hydroponic fertilizer is ideal for this, because it is easily absorbed and contains all essential nutrients. I use General Hydroponics Flora fertilizer, using 1 teaspoon/gallon (5 mL per 4 liters). After 6-8 weeks, you may switch to granular fertilizer that contains micronutrients (I use this). Or continue feeding weekly with liquid fertilizer at 1/8 strength.
Repot your plants to a larger container whenever necessary. Protect your plants from frost the first winter or two. Also keep them fairly dry during the winter, unless temperatures are above freezing. In very hot conditions, you may want to give them some afternoon shade.
While the plants are fairly drought tolerant, they grow the fastest when given adequate water, so avoid letting the soil completely dry out. Don't let the pots sit in a tray of water. If you are in a heavy rainfall area, use extra perlite, pumice or coarse sand in your mix.
I recommend protecting your plants from frost for at least the first winter or two. Puyas will probably flower soonest if protected from prolonged, hard frosts.
By the way, the leaves will develop a white powder on them. This is normal!
Have fun growing them!
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