Thuja Green Giant – Still Number One Evergreen

It took almost 60 years for today’s most popular hedging plant to attract serious attention. It began as a seedling in a nursery in Denmark in 1937, but it was only after plants were grown at the National Arboretum in Washington DC that its remarkable properties were noticed. Success followed quickly after that, and very soon new plants were being created in their millions and snapped up by gardeners all across the country, eager to replace old hedges with something new that wouldn’t take a decade to look good.

Fastest Evergreen There Is

Thuja Green Giant certainly satisfied that need for speed, and it remains the fastest-growing evergreen around. Such claims are made for many plants, but this one has research to back it up. In trials at the University of Arkansas, tiny plants grew to 10 feet tall and were 5 feet wide after only 7 years. In the early years growth rates of over 3 feet a year were shown by the young plants.

These were plants growing in an open field, with just a little irrigation in summer. In a garden, with well-prepared soil, a solid fertilizer program, and plenty of water, growth in excess of 3 feet can be realistically expected in the first 3 years, falling to about 2 feet a year after that, and slowing to about 1 foot a year when the plants are mature. That is ideal, because once you reach the height you want, having to trim off 1 foot a year is fine, but trimming much more could become a real chore.

The reason for this rapid growth lies in the origin of the plant. DNA analysis has shown that it is definitely a hybrid, between the Western Redcedar, Thuja plicata, and the Japanese Arborvitae, Thuja standishii.  One grows in Oregon and Washington state, and the other grows in Japan, and they must both have been growing near each other in that Danish nursery. Such hybrid plants show something botanists call ‘hybrid vigor’. The weaknesses of each plant are masked by the strengths of the other, so the child of this meeting is stronger, faster-growing, and healthier than either parent. It is the same thing we see in many food crops, which are also hybrids.

Winter Hardiness

That hybrid vigor also helps make Thuja Green Giant really tough and resistant to cold. It stays green, unlike many other evergreens, that turn brown or bronze in winter, looking less than attractive. Rich green all winter – that what the Green Giant brings. It is completely hardy right through zone 5, and also in warm areas through zone 8 and even into zone 9. Almost wherever you live you can grow this plant easily.

If you do live in a colder area, you would be better choosing an improved form of the native white cedar, such as Emerald Green Arborvitae, which is hardy all the way into zone 2. Wow, minus 50 degrees! Although the white cedar or arborvitae turns bronze in winter, Emerald Green doesn’t, so it is worth using it, rather than cheaper ‘wild’ plants that are often offered locally.

If you live in a very dry area, like Arizona or New Mexico, or in zone 9, consider growing the Italian Cypress. This plant is not as fast growing as Thuja Green Giant, but it needs much less water, and it is renowned for its drought resistance. Its color is very dark green, and it makes a cooling background in a hot, sunny garden.

Rarely Bothered by Pests

Because of that hybrid vigor we mentioned, Thuja Green Giant is only very rarely seen with any serious pest or disease problems. Almost every grower reports that the just don’t see more than the odd patch of pests, which quickly disappear, and diseases are usually the result of very poor growing conditions, for example planting in soil that is always wet and boggy. Although it likes a regular supply of water, good drainage is important, so that air gets to the roots and keeps them healthy. If you do plant in a low-lying, always wet area, dig a raised mound or ridge, a good 6 inches above the level of the surrounding soil. Dig out soil and throw it up to make the mound – the resulting low area then acts as a drain. On this mound the soil will be drier, and your plants will thrive, while still having access to the water from below.

Deer Resistant Too

In many areas, deer are a real problem, and although we have to be careful to say ‘resistant’ and not ‘deer-proof’, many people do report that Thuja Green Giant is not bothered by deer. This is very different from many other evergreens, which are breakfast, lunch and dinner for local deer. There are lots of horror stories of gardeners spending years growing a nice Thuja hedge, only to see it one morning in winter stripped of all the lower branches and made completely useless. That seems not to have happened with Thuja Green Giant, so you can use it with confidence.

Deer are very unpredictable, and if hungry enough they will tackle anything, so if you do have regular deer in winter, spraying with a repellant makes sense. To turn your hedge or screen into a deer-proof barrier for your whole garden, add a chain-link fence, 2 or 3 feet behind the plants. Let the hedge just grow through it, and deer with never get through. You can never be too careful when it comes to those adorable but pesky critters.

Worth a Little Care

With a plant that is so easy to grow, neglect is still not the best approach. Spend some time and effort digging the area you are going to plant into. Add some rich organic material, such as garden compost or rotted manure if you can find some. Even peat moss is worthwhile if nothing else is available. When planting, allow 3 to 5 feet between plants, depending on how quickly you want them to fill in, and how wide you can let your hedge or screen become. For an untrimmed screen, 5 feet or even more is best. For a hedge you plan to clip regularly, 3 or 4 feet apart is about right. In the first year water deeply once a week, getting the water at the base of each plant, but also on the surrounding soil, to encourage the roots to grow outwards. In later years water during hot, dry spells. Have a simple fertilizer program, especially for the first few years. It really pays off. Slow-release fertilizer will last a whole season from just one spring application. It is more expensive, but the time saved is often worth it. Finally, clip right from the get-go, so that you build a dense structure. Waiting until you reach the final height is a common mistake. Just a light trim is all you need as your hedge develops – it really pays off in the future.