Yucca filamentosa 'Colour Guard'
The exotic and tropical appearance of this sport of Yucca filamentosa belies it UK hardiness credentials. Officially the RHS rating is H5 which means it can tolerate temperatures down to the -10°c to -15°c. Unofficially reports of temperatures as low as -30°c in the states have been recorded with this Yucca surviving. One caveat being that it like free draining soil so planting in a rain shadow or on raised ground is sensible.
The official name is spelt the American way Yucca filamentosa 'Color Guard' but if you are looking to buy the Color Guard Yucca (aka Adams Needle or Variegated Needle Palm) then most UK sources showing it for sale list it with the British spelling.
The strappy leaves are softer than Yucca gloriosa making it safer to plant out where people are likely to get up close to it. As with all sports of filamentosa you get the filament like threads which appear from the edge of the sword like leaves.
From a distance its appearance resembles that of a type of grass but with wider more colorful blades. It seems to do better with more sun compared to being overshadowed or shaded by other plants so not ideal for shady spots.
As you can see from the picture the variegation of the foliage is not uniform and the ratios and patterning of the greens and yellows makes it look less formal and more tropical.
The outer edges of the leaves are predominantly a mid green colour with yellow to butter yellow centres. It makes for a bold and bright plant.
Other Variegated Yucca filamentosa
The other variegated alternative is Yucca filamentosa 'Bright Edge' which in my opinion is not as good visually as the yellow is on the outer edge of the leaves rather than the centre making it less visual.
It is also not as hardy being only H4 which is -5°c to -10°c which is not bad but 'Color Guard' just seems more superior overall.
Although not filamentosa there is also Yucca flaccida 'Golden Sword' which look like the twin of 'Color Guard' however it it not as hardy also being rated at H4 (-5°c to -10°c) for winter hardiness although Burncoose lists it as half hardy and only suitable down to -5°c.
There are two types of Yucca seen growing, the more commonly seen trunk forming varieties such as Yucca Gloriosa with the large upright flower spikes in summer. The second type which covers Y. filamentosa are the clump forming types that do not form trunks.
I originally got into clump forming Yuccas as a hardier alternative to the smaller more colourful Phormiums. In my experience in cold winter winds Phormiums tend to suffer wind burn on the leaves which tends not to happen to Yucca.
Colour Guard Care and Pruning
In a cold tolerant tropical looking evergreen garden you want plants that good all year round. Even if it's too cold to go into the garden you still want to be able to look outside onto a lush colourful garden and not an area or brown sticks.
Yucca does not require much in the way of ongoing care or maintenance. After the flower spike has finished you can cut the flowering spike off. As the lower leaves die off you can tidy the plant up by removing them.
You shouldn't need to water this plant which makes it ideal for the longer drier spells we seem to be experiencing in the UK, especially in the summer.
What to Expect from 'Color Guard'
As this plant is evergreen it remains in leaf all year round and doesn't lose its leaves in winter. In winter you may notice the yellow part of the leaf turn a pinkish red colour which adds to its appearance. As the days lengthen and the temperatures rise the yellow returns.
The variegated Yucca such as this Yucca gloriosa variegata (pictured) can turn pinkish red in winter which is similar to the colouring of 'Color Guard' during winter. An added bonus of the variegated or coloured versions in the Yucca family.
In the summer it may produce a white flower spike which can be as tall as 2 metres but generally shorter. Unlike some other types of Yucca the plant may die back after flowering but it would have been replaced by younger suckers from around the main plant. Eventually over time this will build up to a clump of rosettes.