Left:Phormium 'Sundowner"; Right:Hebe 'Amy'Many gardeners in the Seattle area have noticed considerable damage to landscape plants such as phormiums (New Zealand Flax) and hebes due to our recent December snowstorm. The extent of this damage is the worst that I have witnessed since the winter of 1990. Among my own plants, Phormium 'Yellow Wave' and a variegated form of Pittosporum tenuifolium appear to have been affected as well. The combination of snow, moisture and several days of subfreezing temperatures created the perfect conditions to either severely damage or even kill a large number of marginally hardy plants in our region.
It is likely that most marginally hardy plants that had been sited in wet or poorly drained areas would have perished in this most recent event. Others at risk are those that were planted last fall and were not well-rooted. The plants that have the greatest chance of survival are those that were established and had good drainage to begin with. Nevertheless, before jumping to any immediate conclusions, I would perform a thorough examination of any plants in question. Once you see how severe the damage is, you can make a decision based on whether the plant can recover within a reasonable time period or if the cost of its replacement is acceptable. Since many of these plants are in very prominent locations, you may not want to wait until summer to fill certain voids left by any dieback.
When inspecting a phormium, even if all of the large grass-like leaves may be brown and/or dead, pull firmly on the leaves near the base of the plant. If they are firmly attached and do not pull away like limp muck, there is a good chance that the roots are in good shape and the plant should regrow from the base by summer. I would go ahead now and cut the leaves back to roughly 6" from the base. If another cold snap is expected later this winter, I would plan on covering the crown with pine boughs, burlap, or other protective covering.
To properly inspect a woody ornamental such as a hebe or Spanish lavender, I would try to wait until late March when temperatures can begin to encourage signs of growth such as budding on the stems below any branch dieback. At this time, you would be safe to prune or shear them back until you can see that the stem tissue is alive. If you scrape the outer bark on the stem with your thumbnail, you can see if the wood is alive if you detect a thin later of green tissue (cambium) just underneath. In the event that the plant is still alive, you must also check to make sure that the base(stem) of the plant is not buried by soil or mulch. If the plant needs protection from the cold in the coming weeks, wrap it in burlap or a sheet.
If your plant appears to have some hope of recovery based on what I've mentioned above, continue to monitor your plants weekly through the spring for signs of life and consider applying a generous layer of compost mulch with a bit of steer manure and all-purpose fertilizer worked in (don't bury the stems!!!). This should encourage growth later this spring when the temperatures outside begin to warm up the soil. For those who wish to resort to water-soluble synthetics (ie. Miracle-Gro), wait until at least early April. I hope that this can offer a glimmer of hope to some but only time will tell. Best of luck to all. I'll try to make my next post more pleasant. Cheers, Tim
