The short answer to this question is ‘NO’, but despite the toughness and resistance of this great evergreen, problems can very occasionally develop, some caused by growing conditions and some by specific pests or diseases. Don’t worry, these problems are rare, and most gardeners never see any problems at all with their plants. So that you can be equipped to deal with anything that may seem to be going wrong, it’s time for some advice. So here are some things you may see, and what to do about them.
My new plants look dull and the ends of some of the branches are turning brown
New plants of Thuja Green Giant need plenty of water. When they are first planted they only have roots in the root ball from the pot. Especially if the surrounding soil is a bit dry, those roots won’t be able to take up water and this will first show by the ends of the branches bending over and beginning to turn brown. If the weather is warm you may need to water your plants every second day for the first few weeks after planting. Otherwise water them at least once a week. New plants need plenty of water to establish in your garden, so don’t forget them – they need you!
My plants look yellowish, not bright green, and they aren’t growing
Especially when young, these fast-growing plants need lots of nutrients. They don’t have a big root system yet to get enough from the soil around them. So they can easily run low on essential food elements, grow more slowly and show a characteristic yellowing of the leaves. If you see this, it is time to start fertilizing your plants. For young plants choose a water-soluble fertilizer formulated for evergreen hedges and apply as directed. If your plants are older, then a granular fertilizer will be lower-cost and quicker to apply. Modern slow-release fertilizers cost a little more, but they only need to be applied once a year and they will continue to feed your hedge all season long.
There are strange-looking clusters of dry needles hanging in the tree
These could be bagworms. This is a common pest of some arborvitae trees, and it is occasionally found in Thuja Green Giant. Since this tree is so tough and hardy, they are only very rarely attacked by this insect. If you see what look a bit like hanging greenish or brown ‘cones’ one or two inches long on your plants, then you have bagworms. Inside there is a green caterpillar that will eat the leaves, and can make parts of the bush very bare. If you just have a few, or your plants are young, then simply pick them off and throw them into a bucket of hot, soapy water. The caterpillar makes the bag out of silk and pieces of the plant it has chewed off. Once you remove the bags your trees will quickly grow back. If you have larger bushes, or a lot of bags, then spraying with Bt (pronounced ‘bee-tee’) or Spinosad. Ask at your local garden center for specific brands of these safe, non-toxic sprays made from naturally occurring microbes. These products only kill caterpillars and they will not hurt other insects, animals or humans. Since bagworms usually don’t attack Thuja Green Giant at all, you will probably never see this pest on your hedge.
I have something sticky on my leaves, and black powder on them too
Again, this is a very rare problem, but it can happen. The stickiness comes from sap being taken from the plant by scale insects. The black (or occasionally white) growth is fungus growing on the sugary sap. Neither the sap or the fungus will hurt your plants, but the little scale insects, that look like brown pimples on the stems, do weaken the trees and can cause browning. Luckily Thuja Green Giant grows so fast and so vigorously that scale is rarely a problem. If you see areas like this, usually you can trim them away, clean up carefully, feed and water your trees and they will quickly recover. Only very rarely, perhaps if your trees are growing in poor, dry soil, will scale be bad enough to need spraying. Ask at your garden center for something suitable.
Poor growth, and branches are dying
Although your trees need water, they can have too much of a good thing. If the soil is constantly wet no air gets to the roots, and they die and rot. If your plants are not growing, well, and parts of them turn brown and die, or if a whole plant in your hedge dies, you may have root rot. Once the symptoms show it is hard to do anything, so first make sure you plant in an area with good drainage. If you need to plant in a badly-drained spot, then mound up the soil and plant on that mound. If the plants are a few inches above the soil the roots will get more air. If you have an irrigation system, check that you don’t have a leak, or reduce the watering time. Your plants should get plenty of water, but the soil should become a little dry in between each watering.
In the End
Thuja Green Giant is one the most pest and disease resistant plants you can grow, so if you give them a little basic care with water and fertilizer the chances are very good you will never see any problems at all. Now that you know what to look for, you can take some simple steps to deal with any rare problems that might come along.