Grevillea
Exotic shrubs that bloom year round- Cold tolerant varieties
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 a very large hole, loosening the soil around the edge, this makes it easier for the shrub to root into the surrounding soil. Water well until you see good new growth then ease off. If your Grevillea is slow to kick into growth you may water it more- about once a week. Grevilleas are adapted to such poor conditions that water can almost be considered having the effect of fertilizer. So, remember that just water makes them GROW. Established 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 can kill them and fast. 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, and for upright varieties even without irrigation it is advisable to prune them regularly to make sure that underground root growth mass matches top growth. This is less important on lower growing varieties. 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. As with many plants the more established a Grevillea, the hardier it will be to cold. For instance a three year old Grevillea will be many times hardier to cold than a newly installed plant. As they become established and root out they gain hardiness to cold and resistance to frozen soil. Plant them earlier in the year and meet their requirements going into their first winter and all will be well.
The cold hardiest species and hybrid derivatives of those species make up the majority of species/ cultivars that we grow. The hardiest by species/ cultivar in this order are: Grevillea australis, australis prostrata, victorae ‘UBC Form’, Grevillea juniperina sp. and the cultivars ‘Neil Bell’ and ‘The Precious’. These species are recommended for the coldest gardens. Of course warm microclimates may allow you to grow even more species, but if you live in colder rural areas, I would stick with these and put them in a warm microclimate- such as a south facing wall or alcove, or at the top of a hill where cold air drains away. Overhead protection of evergreens is also useful. Grevilleas, once established will compete admirably with large tree roots and endure the dryness. As long as they receive at least 4-5 hours of direct sun or even very high overhead shade ( a very tall tree canopy) the added protection of an overstory adds quite a bit of cold hardiness. In this circumstance added irrigation may be needed to spur root development and establishment. Established shrubs are not only extremely drought tolerant they are also much hardier to cold.
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- Banksia, Embothrium, Hakea, Lomatia, and Telopea average, un-ammended soil with NO supplemental fertilizer and compost. Avoid watering during hot weather.
Climate Adapted Plants for Gardeners in the PNW
