Exotic shrubs that bloom year round
We are fascinated with this genus of plants native to Australia. The vast majority of the nearly 400 species are shrubs which are what we grow. Australia is a big country but the areas that receive truly cold weather are restricted to the highest mountains and alpine valleys. Not surprisingly species from the highest elevations of the Australian alps have proven to be fantastic garden plants in our climate- and there are many more species and cultivars waiting to be tested here.
Grevilleas are members of the Proteaceae. That family which is ancient is almost exclusively from the southern hemisphere. Proteaceaous plants have several peculiarities that are important to understand to succeed with them. The soils they are adapted to are universally old and poor and to thrive in those conditions they even form what are called Proteoid roots. These are fine, fine, clusters of roots that can extract the most microscopic nutrients from depleted soils. This has made them very sensitive to overly enriched soils and the substance phosphorus is particularly toxic. Avoid all fertilizers.
So, what they require to thrive- and we’ve grown them in this climate for more than 20 years- is just a whole lot of neglect. Do not enrich the soil, even with compost. Our native unimproved soils are exactly what they require. The best way to approach planting a Grevillea (or any Proteaceaous plant) is simply to dig the hole, plant, and water the plant if it gets dry until you see good new growth. Then cease. Grevilleas are supremely drought adapted and are best left to subsist on only what falls from the sky. Its important to avoid watering them in hot weather. The combination of wet/hot soil will kill them- almost immediately. Neglect. It works.
We love them for their varied textures as well as propensity in our climate to bloom continuously- including all through winter. Give them a slightly protected location such as a south or west facing aspect in as much sun as possible. During the winter I have a permanent “flock” of Hummingbirds who harass my shrubs- one of the few nectar sources in winter- and they know it. If you want hummingbirds this is the number one shrub to plant.
Nearly all grow very very fast, even without irrigation and it is advisable to prune them regularly to make sure that underground root growth mass matches top growth. If above ground growth is too rank it can rock the whole plant in gusty weather. Up to 1/3 of the mass of the plant can be removed annually on well established plants.
The flowers on cold hardy Grevilleas are uniquely adapted. The flower buds are clad densely in fine hairs which actually insulates them from extreme cold. Open flowers are cold hardy to about 24ºF but masses of protected buds hardier to much lower than that always wait in the wings to be replaced those damaged by frost. So, the floral display is briefly interrupted but quickly resumes with a thaw. Also, if your plant is shy to flower at first, we have found that light tip pruning- just 1/2″ off of each tip will spur them into bloom, increasing blooming wood as well as plant density. This may be done at any time of the year.
The same cultural requirements can be found for other plants in the Proteaceae- Embothrium, Hakea, Lomatia, and Telopea average, un-ammended soil with NO supplemental fertilizer and compost.
Climate Adapted Plants for Gardeners in the PNW