Tuesday, January 1, 2013

Why Won't My Stanhopea Bloom?

This is one of the most common questions I receive from orchid growers.  Another related question is why do Stanhopeas not bloom consistently each year? The answers are not necessarily straight forward and all encompassing.  Some of the reasons why Stanhopeas do not bloom are because they are too immature to bloom, are planted in the incorrect media or containers, the general growing conditions are not understood well, and that they are not given proper care.
Stanhopeas only bloom on mature pseudobulbs, so if you purchase a seedling instead of a division of a plant, then it may be a few years before your plant blooms.  Small seedlings of only two years of age may take five or more years to mature.  Recently divided plants may not bloom for a year or two, and take time to recover depending on the size of the division and the time of year that the division was taken.  Repotting or re-basketing may also delay bloom of Stanhopeas for a year or more.  Several growers have reported that they have no setback in bloom times from dividing or repotting Stanhopeas.  However, I have been following this more carefully over the past few years and have recorded approximately 50 percent of my Stanhopeas negatively impacted due to division or repotting.  Most of the ill effects are lower flower counts on the inflorescences, or early termination of new inflorescence growth.
Stanhopea panamensis - second flowering of the
year in December after main flowering in October.
It is advised to grow Stanhopeas in baskets because they produce pendent inflorescences that grow through the potting media .  I have received several Stanhopeas from people who did not want the plants any longer because they could not get them to bloom. When I received the orchids I found they had been grown in pots, not baskets.  When I repot the plants into a basket, I often find several old inflorescences that could not grow out of the pot from the last flower season.  After re-basketing, the plants began to flower normally each year.
Knowing the proper care provided to the species of Stanhopea you are growing often leads to an increase in flower production.  Some species such as S. annulata, S. avicula, S. candida, S. cirrhata, S. ecornuta, and S. grandiflora (including several others) require more tropical night temperatures throughout the year and bloom best when winter night temperatures do not drop below 65F (18C).  Other Stanhopeas inhabit areas where they receive less water and more sunlight during the winter months.  These Stanhopeas that require a rest period include S. hernandezii, S. insignis, S. jenischiana, S. leitzei, S. maculosa, and S. martiana.  I usually place these Stanhopeas under a roof overhang or under a plastic roof during the winter so that no rainfall can penetrate the growing medium.  I then keep these sparingly moist, but never let them completely dry.  I start regular water of these species in mid spring, when growth starts.  For these Stanhopea, the dryer conditions and increased light during the winter tend to force them to enter into a rest period that they require in order to flower well in the following spring/summer.
Stanhopea panamensis - close up. 
Once your Stanhopeas increase in size they
often will bloom more than once a year.

One common problem Stanhopea growers share is that they are unsuccessful in consistently blooming their Stanhopeas in greenhouses.  In fact, Barney Greer mentions several species (S. florida, S. maculosa, and S. platyceras,) that he had growing in a greenhouse in Sydney, Australia that refused to bloom until he divided the plants and placed them to grow outside.  During the next flowering season the plants began to flower regularly.  The reason why this may occur is that some species of Stanhopea bloom more profusely with a 20-30F (approximately 10-15C) degree shift between day and night temperatures.  These shifts in temperature are best achieved by growing the orchids outdoors in the spring and summer.  Since several species of Stanhopea can grow and bloom well outdoors in southern California, I choose to grow my collection outdoors year around, and then shelter those that need either more warmth, or less water in the winter months.  If you cannot grow your Stanhopeas outside the entire year, try growing them outside in the spring and summer months.  Most growers that have tried the technique of growing Stanhopeas outside when the temperatures are warm enough have had an increase in success flowering their plants.
Additional care that can cause inconsistent flowering includes too little water during the growing season, or being placed in too much sun, and not enough humidity.  When I first began growing Stanhopeas, I placed them in a specific location that received dappled sun throughout the day.  The tree that provided the shade had lost some foliage and branches and one of the Stanhopeas was severely burned.  The plant could no longer grow in that location, with too much sun and not enough water and humidity throughout the day.  I repotted the Stanhopea and placed it in more shade.  The plant slowly recovered and new growth began, but after that improper care, the plant did not bloom for five years.  Just remember that if your plant has some type of a setback or improper care for some time, it may not bloom for a year or more.
Some individuals find that fertilizing Stanhopeas more can increase flower production.  I only fertilize to ensure that the plants are growing large enough and the pseudobulbs are mature enough to flower.  Other than this, I have found that no other fertilizing is necessary to spur plants to bloom.
Too much shade is usually not a problem, but could be the cause for some Stanhopeas to not bloom.  I usually keep my Stanhopeas on the north side of my house and they either receive dappled sun the year around or indirect sun with the only shade coming from the building.  I often provide a little extra shade by stretching saran cloth over the growing area during the summer months and when temperatures are very high (above 90F or 32C).
If you follow these general guidelines, you should be able to increase your chances that your Stanhopeas will bloom, and do this consistently each year.  Being patent is a requirement though, and it may take several years for your Stanhopeas to produce good sized growth in order to flower.  For reference and indications that your Stanhopeas are growing appropriately, see the post 'How do you know your Stanhopea is happy?'

1 comment:

  1. Hey Robert,

    I'd love to reprint this article in our newsletter with your permission and attribution. Think it would be great for our stanhopea growers.


    Sue sbottom15@gmail.com