The winter flowering gladiolus species are found in areas of South Africa that receive significant winter rains and are typically dry all summer. Some of the species grow in seasonal wetlands that are swamps in the winter, when they are growing, and bone dry in the summer, during which the plants are dormant. Other species are found in drier areas in sandy soils. In practice, culture of most of the winter blooming species requires excellent drainage and abundant water during the growing season and complete dryness during the dormant period. Unlike the summer blooming hybrids that grow and bloom during the summer months, the winter blooming species will not adapt their growth period to any other time of the year. They will inevitably try to grow during the winter when the days are short and the temperatures (in their native lands) are cool. Because of this requirement for cool temperatures they will not do well in a typical houseplant setting. They can be grown indoors if the night-time temperature is cooler than the normal house (upper 50's). However, they like warmer daytime temperatures. If you can successfully grow freesias, then the winter blooming gladiolus species should do well, because they basically need the same growth conditions that suit freesias.

I have grown the a few of the winter blooming species the last three years, so I am by no means an expert. However, this is what has worked for me and is derived from what others with much more experience have written. In Tucson, which provides reasonably good growing conditions in the winter, I have had success growing the species outdoors in ~3 gallon plastic containers. I use a 50:50 mix of commercial potting soil and builder's sand. This mix drains well and is easy to prepare. In my first year of growing, I was worried about overwatering and rot. Consequently, I ended up underwatering the plants. This treatment didn't bother the plants until they flowered, at which time they were transpiring more than I was giving them in water. The bulbs do not seem to form extensive root systems so they do need to be kept rather moist. In the second year, I watered more frequently and did not let the medium dry very much between watering. This suited all of the species I grew. They flowered well and did not rot. However, I did find that too much water, even with the dry climate and well drained soil mix did result in rot problems with xerophytic relatives of the gladiolus, and may be a problem for the xerophytic gladiolus species, which I have not yet tried to grow.

The species that I have tried (Gladiolus caeruleus, G. carneus, G. huttonii, G. priorii, G. teretifolius, G. trichonemifolius, G. tristis & G. watsonius) all seem pretty cold hardy. They endured light frosts (to 27F (-3C)) without damage. I do grow them in a partially protected area and they were covered with a light row-crop cover (Remay) during cold weather. They also took temperatures into the 90's without problems. During the 1999 and 2000 growing seasons, many of the winter flowering bulbs, including G. caeruleus, (I grow several other South African bulbs that have similar cultural requirements) failed to emerge in the fall after watering until the temperatures dropped into the 40's for lows and low 80's for highs. After a week of cooler temperatures, these species rapidly emerged. This behavior suggests that many of the species sense temperature and wait until it cools before risking growth. In addition, several different bulbs, including G. trichonemifolius rotted in the 1999 season most likely due to being watered before they were ready to grow. In the fall of 2000, I watered once after temperatures had cooled, and then did not water again until shoots emerged. I also have tried to group bulbs that like to be wet together and those that are prone to rot together. These steps produced much better results. I think it is probably useful to group bulbs by blooming time too, so that the early bloomers can be allowed to go dormant earlier, while the late bloomers can continue to mature. I have not tried to pre-chill these species, but this maybe a way to get an earlier start out here.

In the 2000-2001 season, I tried a suggestion from Jim Duggan and watered with half strength liquid fertilizer (I used Schultz brand) at each watering. The plants were definitely stronger and greener. Most had more buds than in the past and the bulbs were bigger too. Several species, such as G. caeruleus, that had not previously produced bulblets produced many bulblets this year.

A good source for cultural information is:

Cape Bulbs

by Richard Doutt
Timber Press, Portland OR
Published 1996