Evergreens are as the name suggest - Evergreen. This means they slowly shed and replace their leaves throughout the year and remain evergreen. They are the opposite of Deciduous trees which shed all of their leaves before the start of the cold season and remain leafless until it warms up. In the UK there are only five native Evergreens. They are: 
  • ​Box (Buxus sempervirens) - this is typically a bush and is found mostly in the Southern parts of the UK
  • Holly (Ilex aquifolium) - A common tree or shrub throughout the UK
  • Juniper (Juniperus communis) - Typically a large shrub. On the decline
  • Scots Pine (Pinus sylvestris) - As the name suggests this is native to Scotland. A tall tree that can live up to 700 years
  • Yew (Taxus baccata) - Often found in Churchyards. All parts of the tree are toxic
Holly is probably one of the most well know evergreens. There are over 600 types of Holly, 
Nearly all conifers are evergreen. The leaves of Lawson cypress are soft and grow in flat sprays.
Although we only have five native Evergreens and over fifty native Deciduous trees in the UK, there are many non-native trees. In fact there are well over a hundred non-native trees in the UK. Some of these were brought over by the Romans but quite a few were shipped over during the Victorian times. Sadly quite a few people perished in their efforts to get these new and exciting plants back onto our shores. We owe a lot to these brave explorers in getting these seeds and specimens back for future generations to enjoy. There are many firs, pines and spruces scattered across our parks and gardens - most of these being non-native. If we only had our five native Evergreens (Box, Holly, Juniper Scots Pine and Yew) it would be a little boring wouldn't it?
All pine trees are evergreen. The leaves are needles. The Monterey ​pine needles are in clusters of three.
The leaves of the Giant redwood are ​small, scale-like and arranged in spirals. They are quite sharp.
So why do we have Evergreens and not just Deciduous trees? There are quite a few reasons but it's mostly down to the climate. Most Evergreens are found in the cooler Northern climates and most of the Deciduous trees in the warmer Southern climates. Basically there is less sunshine in the North than the South. Also, the winter tends to be more harsh in the Northern climates. When it gets really cold our Deciduous trees go into a dormant state, whilst our Evergreen trees are still very much active.
A snow covered Atlas cedar with mature female cones. All evergreens have to deal with harsh weather conditions such as snow and ice.
Frosts, ice and snow are frequent during the winter and can quickly change the state of water from liquid to solid - which can be lethal for trees. All of our trees have many tiny pipes that get water from the ground (roots) to the rest of the tree (leaves mostly). If these pipes get blocked it can soon lead to the death of the tree. Ice crystals are what cause the blockage and can very quickly destroy the cell membranes in the living parts of the tree.
The famous Monkey puzzle tree with its unique stiff and pointy leaves. It is the national tree of Chile.
This is where our Evergreens come out on top (typically). The tiny needle like leaved are actually very tightly rolled up leaves and use a lot less water for Photosynthesis. Also, the needles are covered in a waxy substance called Cutin which helps reduce water loss as well as making it harder for water to freeze within the needles. There are also AFP (antifreeze proteins) which are used in both Deciduous and Evergreen trees. Plants can also use their stored starch and convert it into sugar which acts as a natural anti-freeze. Although Evergreens do not shed their leaves annually like our Deciduous trees, they do still shed their leaves, but in controlled amounts all year around. A good way of looking at our Evergreens and Deciduous trees is to compare them to as power companies (just bear with me for a minute!). So we have Evergreen Energy and Deciduous Diesels:
"We at Evergreen Energy run all year around - even during the winter! Our amazing Cutin technology helps us against water loss and ice damage making sure our leaves stay healthy. As we don't renew all of our leaves every year we can collect energy any time. We prefer to run our power plants at similar times all year around. Due to our amazing water saving systems we can operate in the cooler regions as well."
"We at Deciduous Diesels collect more energy during the summer than the winter. We shut down our power plants during the winter to save water and energy. By getting rid of our leaves each year we ensure they don't get damaged during the winter. The old leaves fall to the ground and we re-use the energy via our root system. We typically collect energy from the sun throughout the year at different levels as per below:
Spring - 25%
Summer - 50%
Autumn - 25%
Winter - 0%
FACTS & INFO
  • Evergreen trees thrive on every continent, with the exception of the Antarctica
  • The tips on the young branches of some evergreens provide vitamin C
  • Some people have used evergreen pitch for sunburn prevention
  • Norway spruce is the most common Christmas tree in the UK
  • Bay leaves are often used in cooking (tasty curry) and are Evergreen
  • Other edible Evergreens include Artichokes, Sorrel and Rosemary
  • Pine pollen is harvested and used as a food source and also has medicinal purposes
  • Evergreens are used for softwood (timber and paper mostly)
  • Yew leaves are used in the treatment process for chemotherapy
  • Yew leaves are highly toxic and can easily be confused with other evergreens. Beware!
  • Evergreens are conifers. But not all conifers are Evergreen! Larches are an example
  • Resin is produced by Pine trees and has many uses including glue and varnish
  • Evergreens make their own type of antifreeze. These are Jasmonic acid, Ethylene and Glucose
SCIENCE STUFF
  • AFP - antifreeze proteins. Turns out it's not just plants that have them! Wikipedia covers this well
  • Anthocyanin -a red pigment in the leaves
  • ​Carotene - a yellow / orange pigment in the leaves
  • Chlorophyll - the green pigment in the leaves
  • Conifers - a group of trees that are mostly Evergreen. They are gymnosperms (cone-bearing seed plants)
  • Cutin - a waxy water-repellent substance in the cuticle of plants. An insoluble mixture containing waxes, fatty acids, soaps, and resinous material
  • Deciduous - a tree or shrub that sheds it leaves annually, typically in the winter
  • Evergreen - a plant that retains green leaves throughout the year
  • Photosynthesis - typically done within the leaves. A clever process of using light energy from the sun and changing it into chemical energy which is used by the plant. It requires carbon dioxide and water to make this work. Oxygen is released as a waste product
  • Sugar - this is made during Photosynthesis (amongst other things). It is very important and converted into other useful components such as starch or cellulose. Sugar acts a natural anti-freeze