Indian Paintbrush is the common name for the genus Castilleja. They have a reputation for being hard to grow and very few nurseries offer them. I first saw them growing in pots back in the early 1990s when we shared a greenhouse with Jeff Ottersburg of Wild Things. He was growing Castilleja integra (the one that grows wild all over our part of Colorado) and I was fascinated by this. He said it wasn’t so hard, they didn’t even need cold stratification, they would germinate at 70 F.Thanks to Jeff’s advice, we’ve been growing them ever since, and this year I thought, why not try some of the other less common castillejas? This year I’m experimenting with C. chromosa, C. angustifolia, C. haydenii, C. scabrida, and C. applegatei. Unlike Castilleja integra, these others do need to have a period of cold stratification, so I gave them the four to six weeks required and then moved them into the greenhouse. At the moment all but C. applegatei have germinated. It’s kind of exciting and I’m picturing the garden filled with paintbrush in shades of orange, red and purple.
There’s only one problem, and it’s a major one. As easy as they are to germinate and grow in the greenhouse, they’re equally hard to establish in the garden. If you search the internet for information on these plants you will find lots of sites that say they are difficult to grow because they are semi-parasitic. My best understanding of this is that by being defined as a semi-parasite or hemiparasite, castilleja doesn’t absolutely require a host plant to survive but that it does better….maybe…if one is around.
There’s also quite a bit of information floating around about the need for mycorrhizal fungi when growing castilleja. Some research seems to point to the conclusion that it’s not a host plant that is needed; it’s the mycorrhizae in the soil that enables castilleja to take up nutrients. It’s hard to spend much time in the gardening world these days without hearing about mycorrhizae. Mycorrhizae is defined in the American Heritage science dictionary as “the symbiotic association of the mycelium of a fungus with the roots of plants,” or to put it in my own words, the beneficial relationship of roots with a fungus. For the last few years we’ve been using a potting soil mix that has mycorrhizae in it, hoping to help the roots become healthier and more able to withstand drought stress.
Patti Kreiberg, from the Regional Parks Botanic Garden in California, believes that the host plant makes a path for the weaker roots of castilleja to work their way into the soil. She also feels that planting paintbrush in an established garden with other native plants like Artemisia or blue grama will help to ensure that there are the necessary mycorrhizae in the soil already.
Even though our potting soil contains mycorrhizae, I’ve decided to add some native soil to each pot as I transplant them, sort of a double whammy for the beneficial fungi. There is unimproved soil on the ridge behind our nursery, soil that has never been gardened or tilled, soil that looks much as it must have looked 500 years ago or more, so I took a trowel and scooped a small amount for my project. At the moment my tiny paintbrushes are months away from being ready for the garden, but I’m already planning a spot for them in the no-water garden. I’m feeling so thrilled by my five species of castilleja, but according to Intermountain Flora, there are over 200 species, most of them native to the western U.S. How can a gardener ever be bored? ]]>