I ran the following post, as you can see from the date above, in 2012. It has attracted many comments. I am running it again, below, in order to write about a couple of issues raised by a number of commenters. First, read the post, below, which explains Watsonia culture and shows some photos of the plants blooming in our neighborhood. However, readers cannot find the bulbs for sale. The most likely reason for this is that Watsonias are out of fashion. When gladiolus bulbs began to be actively hybridized, gardeners were dazzled by the variety of color, and bicolors that were being bred, so fewer people were interested in Watsonia, which blooms only in white, salmon, pink, and red. I grow Watsonia borbonica because I live in a Mediterranean climate, similar to that of its native land of Mediterranean South Africa, where the mild rainy winter stimulates the leaves to grow and the dry summers allow the plants to rest a bit before fall rains start leafy growth again. Also, when I have tried to grow Gladiolus, they have suffered from a rust fungus disease. I have seen Gladiolus in nearby gardens that were damaged by thrips insects. Watsonias never seem to have diseases or insect damage. Gladiolus, nevertheless, is probably a bigger seller than Watsonia, rendering Watsonia bulbs, or corms, scarce in nurseries. There is also a second reason for Watsonia's lessened popularity. That is that there is an invasive Watsonia. It is called Watsonia meriana, a summer-dormant species described as bearing dull red-orange, purple, or white flowers in late spring. A variety of this species, W. meriana bulbifera, bears bulblets, or cormlets, on its flowering stems that can reproduce the plant, giving it two means of asexual reproduction (the cormlets could roll away and start new colonies!). While this species is not on California Invasive Plant lists, it has been seen growing wild on roadsides and in fields in Sonoma and Mendocino counties. It is also a pest in Australia, and may partly explain the difficulty of locating Watsonia borbonica corms for sale here and there, since nurseries may confuse it with this other Watsonia and be afraid to sell it. So the first point is that it is hard to find the corms for sale, probably for 2 reasons: Plants go in and out of fashion, and this one has been out of style, and also, the habit of just using its genus name has allowed it to be confused with another, potentially invasive member of the same genus.
So, what to do if you long for this tall, beautiful, low-maintenance plant. I suspect that your best bet is to notice some growing in a garden in the spring and ask the gardener if you can have some corms when they are dormant in the summer. Since the plants you see were probably planted some time ago, when they were being sold, and since they become crowded and bloom less after they have grown in the same place for several years, chances are there will be plenty of corms to spare. I see Watsonias in a number of gardens in San Francisco, and have seen them in old gardens of Pacific Grove (next to Monterey). Probably in areas where they will thrive on the California west coast, you will see some in bloom this spring. Meantime, I can only hope that nursery propagators are listening.
You can read more about Watsonias and 49 more easy care, drought tolerant plants in my book Wildly Successful Plants: Northern California.
In April and May I look for Watsonias. I love these big, graceful plants, with tall stems of trumpet-shaped flowers. These easy-to-grow bulb plants are one of South Africa's best gifts to Bay Area gardeners. They are among the 50 plants I featured in my book Wildly Successful Plants: Northern California, as very well suited to our gardens and easy to grow. (See cover, at right) They thrive in cool or hot summer areas. I don't know of an insect pest or a disease that troubles them, and snails don't seem interested either.
The red one in the two photos above is a hybrid, one of several usually available in nurseries for fall planting.
After you plant the bulbs (correctly, they are corms), the leaves begin to grow with the first rains. They usually don't need any irrigation beyond rainfall to mature and bloom. Even last winter, which was rather dry, I didn't water mine, though I might do so in a really, really dry winter. After weeks of glorious mid- to late spring bloom, they die back in early summer. You don't have to water them in summer either. These are truly drought-tolerant plants! If the soil is well-drained, they won't mind a little summer water, but if kept too moist, they won't bloom as well the following year.
The reason Watsonias do so well here is that they are from the Cape Region of South Africa, which has a similar rainfall pattern to ours. The regions where they grow have poor, sandy soil, so our rather poor soils are not a problem, though they can take moderate fertility, if you want to dig in a little compost. They stand up to wind and cool temperatures. They thrive in foggy microclimates. Full sun is best near the coast, but half-day will do. If you garden in a hotter inland microclimate, they will appreciate the hot soil while they are dormant. The spring-blooming Watsonias described here are hardy to 10° F.
It's best to cut the flower stalks after they bloom and, in mid to late summer, cut brown leaves to the ground, before new green ones start to grow, so that they won't distract from next year's show. The deadheading and cutting back is really the only annual care they need.
Watsonias are grand at the back of a border, where their 5- 6 foot tall flower stalks will be seen over other plants. Another way to grow them is behind a hedge, so they stand above it when in bloom, disappear when they die back. Or mix them into a narrow border with other plants of similar height--shrubs or other tall perennials. In addition to ornamenting the garden, Watsonias make good cut flowers.
Most of the Watsonia plants I see growing are hybrids, with peach, pink, or red flowers, which are readily available at nurseries for fall planting. I also see the pink or white-blooming ones that represent the species, Watsonia borbonica, especially in older gardens.
I think the pink one in the three previous photos is the species, Watsonia borbonica. It is described as having "violet" stamens, and these look violet to me.
This white one may be Watsonia borbonica ardernii, a subspecies that was discovered in the wild.
Plant the corms about 4 inches deep and 6 inches apart. You can plant in a circular area to get a nice clump, or could plant in a row.
While the plants will thrive with little care, if you have time, and want to groom your plants to keep your garden looking at its best, here is what to do:
While the plants are blooming, remove spent flowers every few days. They will fall off in your hand at a slight pull. When the top flower of the central stalk of flowers has bloomed and faded, cut that stalk off where it joins a lower flower branch that still has buds or open flowers. (You will need hand pruners for this, as the stalks are tough). When all of the side stalks have finished blooming, cut the entire flower stalk short enough that the cut end won't be visible above the leaves.
When all of the flower stalks have been cut, you can ignore the plant until all the leaves turn brown, or you can go out every couple of weeks and remove brown leaves. It is up to you. But when all the leaves are brown, cut them as short as you can. You will need sharp pruners to do it. Don't wait until the green "swords" of the new leaves push through in fall, or you will have a devil of a time avoiding injury to the new leaves!
That's about it, until, a number of years later, you might see that the clump is blooming less, or only near the edge, or that it is a bit too wide for its location. Then you might want to go out when the plants are dormant, in summer, and either remove some corms near the edges to reduce the clump size, or actually dig the whole thing up and replant corms.
Either way, you will have some corms to plant elsewhere or to share. Full sized corms are 2-3 inches across and will probably bloom the following spring. Smaller ones (cormlets) will take 2 or more years to bloom. If you dig the whole clump, you will probably have more corms than you know what to do with, and may want to discard the smaller ones. (Or maybe go into the Watsonia corm business.)
One more tip. You can grow Watsonias in a big pot, say 15 inches across for a group of corms, but in a pot you will need to give them a bit more care. From the time the plants start to grow to when blooms are starting to fade, fertilize lightly from time to time, and water regularly. You don't want the mix to be soggy, but unless rain is keeping it wet, water when the top inch is dry.
Learn about 49 more easy, beautiful garden flowers in Wildly Successful Plants: Northern California.