Narrowleaf milkweed is the native host plant for the California Monarch. It's totally magical how planting this in your garden brings the Monarchs. Even when it's a teeny plant, they'll find it.
Over the years I've grown tons of this variety, and I'd be lying to you if I said it was easy. It's a bit fickle to grow. Germinates easily (especially with cold stratification, though I've found it unnecessary), but growing on and transplanting can be a challenge. It's a challenge that's worth the effort though. Of the 20 - 30 seedlings I get started each year, 2-3 make it to the next year. Some are lost to gardener error, others are lost to the monarch caterpillars, which is a great thing!