By Lee Gordon.
Trichostema lanatum, or woolly blue curls, may be San Diego’s most beautiful native shrub, but it has a reputation for being short-lived, difficult to grow, and easy to kill. It purportedly needs perfect drainage, no summer water, and a lot of luck. My experience has been that, in fact, these plants are actually easy to care for.
Water is the key to growing woolly blue curls. They grow wild near where I live, with no summer irrigation, but I have lost plants that I did not irrigate in my garden. On the other hand, woolly blue curls die if they get too much water. Overwatering is the most common way people lose native plants.
I used to watch my woolly blue curls for signs of drought stress, and only watered them then. This happened typically twice during the heat of the summer. The plants stayed green, but they were a dull green and they did not grow. This year, I followed Mike Evans' recommendation to water them monthly with at least one inch of water (Tree of Life Nursery). I do this with an oscillating overhead sprinkler, and it seems to make no difference whether I water at night or in the heat of the day. This summer, the leaves stayed shiny green, the plants grew, and they kept adding their signature spikes of gorgeous blue flowers.
Woolly blue curls do not need supplemental irrigation during the rainy season, but when we have winter dry spells, they grow better and look better if you give them extra water. They need the soil to dry out between summer waterings, but it can stay wet during the cool winter and early spring growing season. The same is true for many of our native plants.
My woolly blue curls grow in clay soil, which is good for many native plants. It holds water well and it is relatively rich in nutrients. Woolly blue curls appear to grow in a variety of soil types. In most soils, they should grow well without any fertilizer. When I plant woolly blue curls, I give the site several inches of water to wet the soil deeply and to give the roots soil to grow into. I want wet soil beneath the hole to encourage roots to grow deeply. After that, they get watered once each month. If your soil drains quickly, you may need to water more often to get the plants established. In time, you should be able to keep them healthy with monthly watering. As you transition plants to longer intervals between watering, keep an eye on them for water stress.
Lee Gordon is a member of the CNPS San Diego Garden Committee with an interest in studying germination and propagation of local native plants. Lee's current research projects include studying methods to create meadows of native wildflowers, and methods to increase populations of the rare, endangered (and very cool) San Diego Willowy mint.