Monthly Archives: June 2019

As the full force of summer arrives, and high temperatures are already being recorded across the country, it is time to think about protecting our plants from drought. With unlimited water and time, or automatic irrigation, it is of course no problem, but many people are making the decision to reduce their garden water usage, either by choice, because of rising water costs, or because more and more cities are placing restrictions on watering your garden, either permanently, or seasonally, which usually means exactly when your plants need it most.

While Thuja Green Giant is not a true ‘xeric’ plant, it does have considerable ability to resist seasonal drought, at least, when it is well established. So the first order of business in making your screens, hedges and specimens of this fabulous evergreen drought-proof is to establish it well. After that we need to conserve the moisture already in the soil, and when we do need to water, make sure we use as little as possible, and get it where it can do the best job of keeping your plants alive. Let’s look at those things in turn.

Establishing Thuja Green Giant for Drought Resistance

Moisture levels in soil increase as we go down, until very often we reach a level where ground water is permanent, and there is abundant water available. In practice that is usually too far down for tree roots to reach, but every few inches deeper means more water, so the first step in making your plants drought-proof is to make their roots spread as deeply as possible. As well, a larger volume of soil from the surface down will make it easier for your plants to find enough water.

Deep Soil Preparation

This is the key, and it means a little extra work when preparing your planting site. Although you may be spacing your plants 5, 6, 7, or 8 feet apart, digging small individual holes is not ideal. A much better approach is to create a broad strip of prepared soil the whole length of your planting, as this exposes a much greater soil volume for your plants to penetrate. Run a string along the route of your hedge or screen, making sure it is 4 to 6 feet inside your property line, and then mark it a minimum of 3 feet wide. If you can, wider is even better. That whole strip should be deeply dug, either by hand to the full depth of a full-sized spade, or by rototiller.

If you use a rototiller, one quick run along the area is not enough (sorry!). It might look great, but that beauty is only ‘skin deep’, and almost certainly you have only tilled a few inches down – stick a spade in if you don’t believe it. Ideally you should pass along the area two or three times, as slowly as possible, and holding the machine back so that it digs deep. By the time you are finished the digging tines should be invisible, and deep in the ground.

Add Organic Material

Besides its nutrient properties, organic material (garden compost, animal manure, rotted leaves, etc.) is a great water-retainer. By adding it to your soil you increase the water-holding capacity greatly, without reducing air penetration, so the roots remain healthy. Remarkably, this is true of both sandy soils, where it seems obvious, and heavy clay soils, which we (wrongly) figure have lots of water in them. [Because they are so fine, clay soils don’t release a lot of the water in them – it remains trapped and unavailable to plants.] So spread a layer several inches thick across the planting area and till it in – it will really make a difference in every soil.

Water to Encourage Deep Rooting

Once planted, your new Thuja Green Giant plants need to spread their roots wide and deep, so they can access as much water as possible in future dry periods. This means watering the right way, to encourage that. At first, for perhaps the first month, the water needs of your new plants must be supplied from the roots in the root ball that was inside the pot – that is all it has. This means watering close to the stem of the plant is essential, and if the weather is hot this might be needed every 3 days. In ordinary spring and fall weather, do it weekly.

As well, we want to encourage those roots to move out from that small volume, and to spread into the surrounding soil you have carefully prepared. They won’t do that if the soil is dry, so you also need to water over a larger area than just where the root ball is. After that first month, avoid watering close to the stem, and focus on deep, weekly watering of a wide band of soil around each plant, or ideally, along the whole row. Get those roots moving out!

Maintaining Established Thuja Green Giant during Drought

Once your plants have spent that first season getting established, we now want to keep those roots spreading, but as we said earlier, getting water to them can be tricky, so we want to encourage independence and conserve what is already there.

Conserve Moisture

The classic way to conserve moisture in soil is with mulch. Any material, from plastic to paper, bark or gravel, that we lay over the soil will conserve moisture by reducing its loss from the surface. Yes, if you don’t mind the look, spreading out the local paper, or the Sunday New York Times, over the ground, and holding it down with a few rocks or some scattered earth, is a great short-term mulch. Even better is a 2-inch layer of that rich organic material you used to prepare the ground. That really is a better choice than bark, shredded wood, or stones, although cost is a significant consideration too. Rich material will rot down in two or three years and need replacing, but it will also fertilize your plants and maintain the water-holding capacity of your soil, so it is a much better choice.

If you don’t want to, or can’t mulch, then keeping the soil cultivated actually conserve moisture. The surface dries, but the broken up soil doesn’t draw much water from deeper down, and acts as a ‘soil mulch’ – it’s a useful tip, as well as keeping your planting looking great and weed-free.

Keep All the Water You Apply

If you have done things right, watering should be a last resort, and only needed during extended dry periods. Even if your plants look sad, if they are well-established, they will stay alive and come back when you can water again. If water restrictions are not in place, the simplest and most obvious way to water your plants is to grab the hose and start squirting, right? In fact, that is the worst way to do it. Large amounts of water evaporate before it reaches the ground – and the finer the spray the more you lose. So you pay for water your plants never even see. As well, you damage the soil surface, compacting the ground and drawing water more rapidly to the surface where it evaporates. (Mulch will of course prevent that compaction, another plus for doing it.)

Much better is to let water trickle gently into the soil from a slow-running hose. It will spread sideways too as the soil becomes wet, although not so much on very sandy soil. Even better is to weave a soaker hose (shown above) in and out through your hedge, as it will gently spread water over a large area, and this method uses a lot less water that standing there with a hosepipe!

The Botany of Thuja Green Giant – Part Two

Most gardening blogs are about how to grow plants, and here on Thuja Green Giant we certainly write lots of helpful and accurate information about that. But there is more to plants than growing them, and as we explained in the first part of this blog, garden plants are also a great door into the world of botanical science. In this and the previous blog we are looking at Thuja Green Giant with a botanist’s eye, rather than a gardener’s. In the first part we looked at the place of Thuja Green Giant is the bigger scheme of things – its position as a conifer, and what makes them special, and where in conifers it belongs.

In this part we will focus on the place of Thuja Green Giant in its genus, and on a botanical description of the plant itself, and its origins. Hopefully this will be of interest to horticulture students, professionals in landscaping and horticulture, and to interested gardeners who want to know more about the plants they grow.

A genus is the smallest grouping botanists use in their classification of plants. We can think of this as like a human family, with each member of the family being an individual species closely related to the other members. Don’t confuse this with the botanical concept of Family, which is a larger grouping of related genera – perhaps closer to our idea of nationality. Thuja is in the family Cupressaceae, which also contains cypress trees, juniper trees and redwood trees. In all there are close to 30 genera in that family, totally about 140 individual species.

Thuja itself is a small genus of currently five species, with two found in North America and three in Asia. These plants are commonly referred to as Thujas, Arborvitae, or Cedars. The last name is confusing, as there is a whole group of other conifers that are Cedars, in the genus Cedrus, and they are very different. Arborvitae is a much better common name, but its use is patchy. All the Arborvitae have stringy bark, which is reddish-brown in color, and grow into tall forest trees with a single trunk, although the Eastern Arborvitae (Thuja occidentalis) is often multi-stem, and it is also not especially tall. The branches end in sprays of small ‘branchlets’ which spread out in a flattened fan shape.

Thuja (and some other conifers) has two types of leaves. Young seedling plants have short, triangular, pointed leaves growing all along the stems. These juvenile leaves continue for at least a year, and we think they are like this to make the seedlings less attractive to grazing animals, so increasing their chances of survival during that difficult period.

As the plants grow taller, they develop adult leaves. These are decurrent – that is, their bases grow down along, and are attached to, the stems. The adult leaves are of two kinds. On larger branchlets they have a sharp tip 2mm (about one-eight of an inch) long, and that is turned up away from the stem. On the flattened branchlets the leaves the leaves are pressed tightly onto the younger stems, like scales, which is why it looks green and ‘leaf-like’. There are four vertical rows of leaves that cover the younger stems completely. So there are two rows of leaves facing outwards, called ‘facial’ leaves, and two rows facing sideways, called ‘lateral’ leaves. The facial leaves are flat, but the lateral ones have a ridge along them, like the keel of a boat.

Botanists use detailed differences between the relative lengths and forms of the leaves to distinguish one species of Thuja from another, while experienced gardeners can often tell by the overall ‘look’ of the tree which species it probably is. Only a botanist can give a definitive answer!

Because Thuja are conifers, they produce cones, although these are not much like the pinecones most of us know. There are separate male and female cones. The male cones are small, at the ends of branches, and consist of just a few thick scales, making a tiny ‘cone’. Pollen is produced in spring from between these scales, and they are carried by the wind to female cones on other trees. The female cones are lower down on the sides of the branchlets, and they are larger, 9 – 14 mm (about ½ an inch). The female cone has 8 to 12 scales, arranged in pairs rotating around a central axis. When young they are greenish and the scales are closed, making a pea-like object. As they mature – which they do in a single year – they become brown and the open, releasing one to three seeds from the inner surface of each scale. Remember? These Gymnosperms produce ‘naked’ seeds, right on the surface of the seed-producing organ, not inside an ovary, as flowering plants do. This means that we see the seeds right there, sitting on the scale. The seeds have a wing of thin, papery tissue on either side, to help them blown away in the wind and spread to new places.

There are two species of Thuja growing wild in North America. In the east we find Thuja occidentalis, a tree of wet areas, and very winter hardy. It grows up into Canada, as well as all through the eastern states, especially around the Great Lakes and in the Appalachians. Trees are typically about 50 feet tall when mature, but there are exceptional trees that reach 125 feet in height. It can be a long-lived tree, where deer and fire do not reach it, and specimens over 1,500 years old have been found growing on rocky cliffs in Southern Ontario. This makes them the oldest trees in eastern north America. This tree is called northern white cedar, or eastern arborvitae. The name ‘arborvitae’ means ‘tree of life’, because a tea made from the foliage is rich in Vitamin C, and Native Americans taught early European explorers and settlers to use it in winter. It prevents scurvy.

In the west we find Thuja plicata, a larger forest tree, usually called western red cedar or western arborvitae. This tree is much taller than its eastern brother, and it often grows over 200 feet tall, in time, with a massive trunk that can be 10 to 13 feet in diameter just above the base. This tree also grows old, well over 1,000 years, with the oldest specimen known being 1,450 years old. This tree is one of the parents of Thuja Green Giant.

The second parent is one of the three Asian species, Thuja standishii. This tree is called Japanese Thuja, and it grows in southern Japan, on the islands of Honshū and Shikoku. It is a forest tree that can grow over 100 feet tall. We have described in other blogs the fascinating story of the origin of Thuja Green Giant as a hybrid between western arborvitae and the Japanese thuja. The other two Asian species are Thuja koraiensis, a species found in Korea and part of northeastern China. It is a small, shrubby tree growing no more than 30 feet tall. The final species in this genus is Thuja sutchuenensis, the Sichuan cedar, from western China. It is a small tree, that may reach 60 feet, although no trees alive today are that tall. This tree was thought to have become extinct, because it was harvested for its fragrant wood. Then a small group was discovered in 1999, and the area is now protected.

These are the trees of the genus Thuja, and we hope this helps you understand more that hedge or screen you have of Thuja Green Giant.

The Botany of Thuja Green Giant – Part One

One of the great things about gardening is its natural interface with the science of botany. There, in your garden, is a whole display of the breadth of the Plant Kingdom. (Or at least the more advanced parts of it, since algae don’t figure much in most gardens.) Mostly on this blog we think and write about the practical side of gardening, the “How Too” stuff, but looking more closely at your plants is an easy way to open the door into the science of nature and understand more about the plants on which we depend. Since Thuja Green Giant is found in many, many gardens, why not start with it? After all, the entrance to science has many doors. With that in mind, for gardeners who want to know more, and for students of horticulture and botany, young and old, here is a botanist’s look at this popular evergreen.

Evergreen or Conifer?

Let’s start right there. In the garden we usually refer to all plants that stay green all year as ‘evergreens. But it doesn’t take much observation to notice that really there are two distinct types of plants in this group. First there are the plants that have similar leaves to deciduous trees and bushes – flat, green leaves that are broad and thin. These are often called ‘broadleaf evergreens’ to distinguish them from the other kind, those with needles, like pine trees, or with green stems that don’t really have what look like leaves at all, but that are green. The first group are just plants that live in warmer areas, and they see no particular need to drop their leaves for winter, so they don’t. Their leaves may live two or three years, and often drop in spring, when new growth comes, rather than in fall. Often they are closely related to plants that do lose their leaves for the winter.

Thuja Green Giant belongs in that other group, which is more correctly called conifers. These plants are very different. To begin with, they don’t have flowers, which botanists define as a structure with enclosed seeds. Instead, these trees are Gymnosperms, and they have their seeds sitting open on a leaf like structure. It is this fundamental difference that put them into their own group.

The History of Conifers

The first Gymnosperms appeared around 350 million years ago, during the Carboniferous age, when the great coal and oil deposits we use today for energy were being formed. Their exact origin is not clear, but they may be evolved from earlier plants that were fern-like, but that produced seeds on their leaves. If you have seen Cycads, those strange plants that look half-fern and half palm tree, you have seen the earliest forms of these plants. Despite their appearance, these ancient plants have large cones that look very like those on pine trees!

Shortly afterwards two other groups formed. Of one, all we have left is the beautiful maidenhair tree, Gingko biloba. Although we might think this was a flowering tree, the structure of the wood and of the ‘fruit’ shows it to be part of the Gymnosperms.

The Different Conifer Groups

The other group formed by that division is today the most widespread and common – the conifers. There are about 1,000 species still with us, and many more extinct ones, since the rise of flowering trees pushed these plants to areas like the far north, where they could compete successfully. Within the Conifers (called Pinidae), are three large groups, called ‘orders’. These are, firstly, the pines and their relatives, like firs, spruce and true cedars – all tree with needle-like leaves. Then the South American tree called Monkey Puzzle, Araucaria, and the Asian Buddhist Pine, Podocarpus, are grouped together with several other conifers not normally seen in gardens. Third we come to the group containing many of our garden conifers, including redwood, bald cypress, hinoki and sawara cypress, and arborvitae. Yew is also included in this last group, which is called the Cupressales. Within it are three ‘families’, and it is in the one called Cupressaceae that we find Thuja Green Giant.

The ability to test the DNA of plants has led to many changes in our picture of their relationships. It is usually not the DNA of the plant itself that is studied, but the DNA of the chloroplasts – those green parts in the cells that carry out photosynthesis. These structures have their own DNA, and since they reproduce inside the cell by simple division, their DNA changes much more slowly than that of the plants they live in. So they are the perfect guide to long-term relationships between different plant groups. Carefully analysis has allowed us to create clusters of plant groups, and to see exactly how they are related. The resulting changes have bothered many gardeners and nursery growers, but they give us a much better picture of the plants around us.

The Genus Thuja

As a result of all this work and analysis, we now know that Thuja, the ‘genus’ of Thuja Green Giant, is most closely related to a whole cluster of genera of popular garden conifers. In that cluster are Chamaecyparis, which has the important and very varied Japanese cypress trees. As well, in that same group, we find Cupressus, the true cypress trees, from both Europe and North America, as well as the Junipers (Juniperus), which are found all across the Northern half of the world. This family is called Cupressaceae, the cypress family.

We can think of a genus as being like a human family which contains, instead of individuals, groups of individuals very similar to each other, called species. Some genera (the plural of genus) are large, while others are small, sometimes containing just one species. The closest relative of all to Thuja is a single Japanese tree called Thujopsis dolobrata, the asunaro tree, which is very similar in appearance to the Hinoki Cypress. Remember that these divisions are in the end arbitrary, and it depends on how big a difference botanists think is necessary to create a new genus, especially when it contains just one species, as Thujopsis does. For the moment at least botanists are keeping it separate, but that could change in the future. The organization of plants into groups is a human activity, which plants are ignorant of. As gardeners we are best to remember that, so that we see the regular changes that occur as man-made, while nature itself remains just what it is.

In the next part of this blog we will look more closely at Thuja and explore its structure and relationships. Who would have thought that Thuja Green Giant could open so many doors into the science of botany!

Thuja Green Giant for Screening and Shelter

A top priority for many people is privacy. No-one likes to be on their property and being viewed by passing cars, nearby homes, or from apartment buildings. The value of a home reflects this – if you lack privacy your home will be harder to re-sell. So adding shelter and privacy is often the first piece of gardening done, and sometimes the only major part – a garden with screening, a lawn area and perhaps a couple of trees is fine for many people.

Our minds tend to jump to hedges when looking for that privacy, but hedges can be a lot of work, especially tall ones, which can be needed if your privacy issue is being overlooked from nearby buildings. So instead of thinking ‘trimmed hedge’, why not think ‘screening trees’ instead? With no trimming needed, a well-planned screen will take care of itself for many years, and once established ask absolutely nothing of you – surely a great thing in these days of us always being busy.

Choosing the Right Plant

Suitable plants for this will be fast-growing – because who wants to wait a decade or more while your screen grows? – and evergreen. While deciduous trees can often be grown quickly into a screen, all through the winter months they are pretty transparent, so the privacy is limited to summer, which is often not enough. The plants also need to be self-supporting without trimming, and they must give cover all the way to the ground. To do that you need plants that are relatively narrow and upright, because plants with broad crowns will always become bare at the bottom, there simply isn’t enough light penetrating to keep the lower branches alive for too many years.

A plant that really satisfies those criteria is Thuja Green Giant. This arborvitae is a relative of the white cedar known to many people in the north-east. A hybrid plant, it combines an Asian and an American tree, and hybrid plants are well-known for vigor, rapid growth and resistance to pests and diseases – this one is no exception, and incredible tough and reliable. Thuja Green Giant is certainly fast growing. Independent trials have shown it to be the fastest of all the evergreen trees. They usually take a growing season to become established, adding a foot or two in height during that time. Then this tree really takes off. For the next several years it will add 3 or even 4 feet a year, so that your trees will easily be 10 to 15 feet tall within 5 years. After that the growth does slow down a little, but by then you have a substantial screen.

Planning the Planting

Often, when putting in a screen, trees are planted too close together. The idea is that this will give a solid screen sooner, but it’s a mistake. Plant too close and each tree will fight with its neighbors, growing tall, yes, but not thickening up. A spindly, narrow planting is the result, which is easily damaged by wind and snow, and which remains open lower down. In fact, the bottom branches will often die in a few years, completely defeating the purpose of the planting.

The goal should instead be to develop sturdy, bushy plants, which Thuja Green Giant will do naturally, and well, if given a little room. For a screen that won’t be trimmed, it’s especially important to give each plant enough room, because they need to stay bushy, without shooting out all over the place, which crowding will cause.

Within seven years even a small plant of Thuja Green Giant will have grown to be 10 feet tall and 5 feet wide, so that 5 feet is a good planting distance apart for a screen. The young plants won’t crowd each other, and they will each develop into sturdy individuals, able to stand up alone, with dense growth to the ground, and no need to trim. You could easily extend that spacing to 8 feet, and still have solid coverage within ten years. Remember too that you don’t need a solid wall to reduce wind-flow and give privacy everywhere except at 90 degrees to the line of your screening. Not only do you reduce the cost of your investment in this screen, you get a result that requires no maintenance. Even when the plants do start to grow together, they are sturdy enough to do that without weakening and being easy for storms to break.

Usually a single row is planted, but if you have more room a double row will give you better screening sooner, and a more solid barrier to noise and wind. Space the two rows 5 feet apart, and stagger the plants, so that each one sits in the gap of the other row. They can be 8 feet apart in the rows, or even more, up to 12 feet, and you will soon have a fabulous, dense screen that needs no work at all.

Initial Care Makes a Big Difference

Thuja Green Giant will certainly grow fast, and well. But some care in preparing the planting area, and in looking after your plants during the first year or two, will still make a big difference.

Soil Preparation – even the best soils benefit from adding some good-quality organic material before planting. Garden compost or rotted manures are best, but almost anything, from rotted leaves to peat moss, is beneficial. Dig good-sized planting holes, three times the width of the pots your trees are in and mix 2 or 3 buckets of organic material into the soil.
Fertilizer – because it takes time for the root system to spread outwards, and for your trees to enjoy that rich soil you have prepared, applying liquid evergreen fertilizer during the first season, and even in the second one. Liquid fertilizers are much more effective on young plants than granular ones, but they are more work, so by the third season you can switch to a slow-release granular formulation that only needs one quick application a year, in spring.
Watering – after planting your trees are still almost completely reliant on the soil from the pot that is around their roots. So for the first few months you should water close into the stem at least once a week, or more frequently during the hottest and driest part of the summer. Keep the surrounding soil damp too, otherwise your trees will have no reason to spread outwards. By the next season the roots will have spread out considerably into the surrounding soil, and you should only need to water during dry periods.