Castilleja miniata in the Aspen. (Populus tremuloides)
I named my late landscape company after Castilleja: Paintbrush Gardens LLC. Now that name refers to my micronursery that supplies my garden designs and also expresses my demented whims in personal plant tastes.
Here is the way I grow paintbrush myself. There are other ways. I’ll list a few at the end.
1. Chose a species that is native to a similar climate as your own. For example, C. applegatei and latifolia have been good for growers in Washington, Oregon, and the UK. I’ve grown many from the lower elevations of Colorado but struggle with our alpine species.
Castilleja sessiliflora is so boring it blends right in while in full bloom. Pollinators still find it. It’s one of the easiest to grow and some forms are pink and/or white.
2. Collect your own seed. For whatever reason, I find my own seed from the last year or two or three germinates better than anything I buy. Usually. Commercial seed is perhaps old or stored poorly. An exception has been the superb seed from Western Native Seed here in CO.
3. Screen that seed. A decent set of screens makes this really fast, or you can do creative things with folded paper (winnowing) or scraping with a credit card (reenacting Pulp Fiction).
4. Store seeds in Fridge until you are ready to sow.
5. Sow out in fall, say October. Just two months of cold strat may not be enough. Three is more reliable. Do it like traditional rock garden plants- low fertility and high porosity soil mix, a fine (not too deep) gravel grit topressing. Use a small 2”-4” pot. (5-10cm)
6. Pull into greenhouse in Jan/Feb. This gets the seedlings going to be big enough to plant this spring, rather than next fall. Bright light and good air movement. Look out for slugs. Fertilize but gently. I grew half a dozen paintbrush species before I had my little greenhouse, so don’t let this step exclude you.
7. Prick out from one another, pair up with host. Letting the roots touch one another so the Castilleja finds the host easily, putting this unhappy couple in their own pot in March/April. I like to use one year old seedlings of subshrubs or other tough, long-lived and deep-rooted plants so they make a sturdy host. Eriogonum have been shown to be one of, if not the best. Use something easy that likes you. If I have enough seedlings, I’ll often put two tiny 1/2”(1cm) plants of paintbrush per host for better odds at having one take. Also obviously pair up with a host that likes similar conditions to the species of Castilleja you are growing. I personally only bother to differentiate between mountain species and desert species.
There was a great study done by Love and McCammon in Idaho, published in Native Plants Magazine, which had at least two big takeaways: Use eriogonums and germinate the hosts and paintbrush separately. One friend of mine feels that seedlings may parasitize one another.
Recently I put tiny Castilleja miniata with Penstemon davidsonii, something that happens in nature.
I remember this better because a friend, David Sellars took a candid shot of me looking at this.
Short but rugged Eriogonum porteri makes a great adaptable host for a number of dry american Castilleja from pot to crevice garden. Nurseries have long used Artemisia frigida or Bouteloua gracilis for Castilleja integra, which is one of the easiest species.
8. Plant out, barerooted, in April/May/June when the plants are still in active growth but before summer heat (And therefore potential semi-dormancy) has set in. If the plants are pretty leafy and grown when you do plant, I suggest pruning half of their tops off to reduce stress to their roots. Water and watch closely as well as protect from chewing bugs who will take away the other half of the plant. I like to shade them for at least two weeks until they show growth. Now, water sparingly or to match their homeland rainfall.
9. Enjoy and boast to friends. Really, savor it. Because plenty of species are not terribly long lived or just don’t persist in gardens. Many species are only permanent in fairly exact conditions in nature, or in disturbed soil which inevitably settle and mature, excluding those pioneer plants. Castilleja from dry places often go summer dormant, so don’t freak out if they turn brown in summer. That dryness and sleep might be what keeps them safe from rotting.
Castilleja flava lived for three, bloomed for two. Maybe I let it get too dry?
Alternately, you can grow them alone until they are sturdy little lone seedlings and you pair them with a host when you plant them in ground in April. I also like to plant them next to multiple plants to give them diverse backup. Seems to help.
C. integra with Echinocereus triglochidiatus. Seems the cactus is not happy about this.
Also alternately, if you do not have a greenhouse or cold frame, you can do your pricking and pairing just a few months later where they grow outdoors, and plant them either the next fall or spring. I think they don’t like life in a pot so that’s why I shoot to get them planted as soon as possible.
I almost hoed this poor volunteer paintbrush. Don’t worry, an earwig ate it a few days later.
Direct sowing. This works if that seed is absolutely ideally suited to your site. I cannot underscore enough the danger that slugs and chewing bugs pose on paintbrush- they must be as uniquely tasty as they are uniquely beautiful. One night and one slug can take out my entire year’s crop of seedlings if I’m not religiously vigilant. Troughs or crevice gardens seem particularly helpful in accommodating species from dry climates and mineral soils.
Some folks have used GA3- gibberelic acid- to bypass cold stratification. I’ve never been good with acid. Some folks use the fridge, but you must watch them carefully in there. Paul Cumbleton in the UK wrote a great article for The Plantsman about growing them without a host, by taking good care of the plants from the early stages, forcing them to make their own food, and having them live and bloom this way.
Nothing like a big, wild, unapologetic Rimrock Paintbrush. Castilleja scabrida.
As hemiparasites, they all seem to have half the root system a plant should have, so they are just more delicate against any kind of stress you give them. In the end, they are elusive for a reason- wonderful and wild. And in wildness is the preservation of the world, right?
(Castilleja integra reseeds around the APEX crevice garden, photo by Tom Freeth)