I am frequently asked for more specific cultural information on growing Hippeastrum, so I will try to address this here.
There is no ‘one size fits all’ formula for growing Hippeastrum species, since they can come from a variety of habitats. I am not addressing here cultural information for the hybrid Hippeastrum that are available in the trade, since I have little experience with these, and I will therefore try to give tips that have worked for me growing my own limited collection of species. Bear in mind that conditions will vary according to the climate you live in.
My conditions here in northern California are as follows: very cool temperatures in
summer, rarely going above 60F in daytime, with night time temperatures around
45-50F. In winter we get light frosts, with temperatures in the 30-45F range.
My Hippeastrum species are grown in greenhouses which raise the daytime
temperature to about 80F on a sunny day in summer, but we get a lot of summer
fog. Night temperatures drop to 45-50F in summer, which I feel is too cool for some species. Humidity is high because of the fog. My bulbs are rarely stressed from heat or low humidity.
The bulbs are grown on raised slatted benches with good air circulation and drainage. The species from the warmest regions are grown on heated benches. These benches are covered in propagation mats kept at around 68F to offset the cool temperatures at night. These benches have been essential in getting some species to bloom reliably and set seed. The greenhouses are not heated in winter, other than these heated benches.
My standard mix for Hippeastrum is a mixtures of horticultural pumice, perlite and finely ground peat. I vary the mix somewhat according to the region the bulbs come from. I use perlite because it is cheap and light. You can replace the perlite with more pumice, if you wish. I have used coir instead of peat, but found I had more problems with soil fungus.
Mix #1: The standard mix. 1/3 pumice; 1/3 perlite; 1/3 peat.
Mix #2: For the epiphytic bulbs such as H. calyptratum. 2/3 pumice; 1/3 orchid bark.
Mix #3: For species that need very dry conditions, such as H. parodii. 2/3 pumice; 1/3 peat. I have also used pure pumice with good results.
I keep all my Hippeastrum very dry. I keep them dryer than the top 1-2” of soil
drying between watering, since some are in deep pots to accommodate their large
root systems, and the medium at the bottom of the pot can remain very moist and
promote fungal diseases. I have never lost a bulb to dryness, and water about every two to three weeks in summer, less in winter (or not at all). Shallow trays of seedlings or small bulbs are watered about once a week. All get a liquid fertilizer with micronutrients with every watering in summer.
I repot all my bulbs very frequently, and I think this is essential to controlling disease and promoting healthy growth. Repotting takes place in the winter and virtually all the Hippeastrum (other than seedlings) are repotted into fresh medium with the old
potting soil discarded. The bulbs and roots are washed, and all old tunics, dead roots and any dead tissue removed to prevent fungal rots. Sometimes I dust with sulfur when replanting the bulbs. The pots and benches are also washed at this time. I have large greenhouses, and very little problem with disease, and I think it is because of these sanitary procedures. If problems are developing from fungal rots (the most common problem with Hippeastrum), it will be noted early when the bulbs are repotted and can be addressed then. If this seems like a lot of work, it is! My Hippeastrum collection is very valuable to me, and worth the effort and I prefer not to use fungicides unless absolutely necessary.
I will follow up with tips on each of the species I grow.