Question 1

Which trees absorb the most CO2?

Accepted Answer

Studies have identified several optimal tree species for carbon storage. When choosing trees to plant, it is important to consider:
- Fast growing trees store the most carbon during their first decades, often a tree’s most productive period.
- Long-lived trees can keep carbon stored for generations without releasing it in decomposition.
- Large leaves and wide crowns enable maximum photosynthesis.
- Native species will thrive in your soil and best support local wildlife.
- Low-maintenance, disease-resistant species will do better without greenhouse-gas-producing fertilizers and equipment.
 
The “best trees” vary by region, so look around local parks to see what’s hardy in your climate zone.
 
1.   Tulip Tree - A beutiful specimin tree with vibrant autumn colour, works hard under rough conditions.
2.  Silver Maple can trap nearly 11,000kgs of CO2 in a 55 year period.
3.  Oak (English and Red Oak) has adapted to thrive in many climates, provides food and shelter to wildlife and is a long living species that over its life time aborbs great quantities of CO2.
4.  Horse Chestnut grows well in cities; its domed top provides exceptional shade which offers passive cooling benefits.
5. Mulberry provides the added benefit of delicious seasonal fruit. 
6.  London Plane is an excellent choice for urban planning, very tolerant of pollution and root-cramping, resistant to cold and disease.
7.  Sweetgum has brilliant autumn colors, is large and long-lived. 
8. Dogwood offers lovely seasonal flowers; this and other particularly dense trees like Black Walnut can store more carbon in a smaller tree.
9.  Blue Spruce, widely introduced as an ornamental, thrives in most northern regions.
10. Pines are the most carbon-effective conifer.

Question 2

When to plant garden trees?

Accepted Answer

Containerised trees can be planted all year round as the root systems are already actively growing within the container substrate. It is important, particulary in the summer to make sure after transplanting that the tree recieved additional water within the first 8 weeks until its own roots grow into the soil below. Additions such as mulches can help retain some moisture but a few moisture checks closely after planting are recommended.
 
Bareroot trees (trees lifted with no soil around roots) should only be planted between the months November to March when dormant. Make sure prior to planting that roots are kept moist and out of sunlight to maximise success.

Question 3

What are the oldest surviving trees globally and within the UK?

Accepted Answer

The oldest surviving singular tree in the world as far as we are aware is Old Tjikko, a 9,550-year-old Norway spruce located the in Fulufjället Mountains in Sweden. 
 
Pando, a colony of quaking aspen, is one of the oldest-known clonal trees. Estimates of its age range from up to 14,000 years old to 80,000.
 
Within the UK the following is a list of the 6 oldest documented trees:
 
- The Llangernyw Yew, Conwy  -   Up to 4,000 years old
- The Fortingall Yew, Perthshire  -   Up to 3,000 years old
- The Ankerwycke Yew, Berkshire  -   Up to 2,500 years old
- The Crowhurst Yew, Surrey  -   Up to 1,500 years old
- The Bowthorpe Oak, Lincolnshire  -   Over 1,000 years old
- Major Oak, Nottinghamshire  -   Up to 1,000 years old

Question 4

How to plant garden trees

Accepted Answer

Preparing the planting hole
Where possible, the planting hole should be at least 1.5 times the diameter and no deeper than the root ball. When digging the hole keep the topsoil and the sub soil separate so that they can be replaced accordingly. Remove any material from the hole such as large stones that may prevent root growth, and loosen the bottom and sides of the hole to make it easier for the roots to establish.
Preparing the tree for planting
Large trees should only be lifted by container to reduce damage to the plant. Remove any packaging, container or bag from the root ball before planting. Where trees are wrapped with hessian and wire mesh, but do not remove these as they help reduce root damage when planting. These materials are bio-degradable and will start to decompose quickly, while the roots grow through the hessian. 
Planting the tree
Place the root ball into the centre of the planting hole. Ideally, the top of the rootball should be raised at least 5cm above the level of the soil. Then backfill the hole and firm down the soil, but do not reuse compacted or poor quality soil in the hole. Instead replace it with a high quality plant substrate.
 
Watering
After planting, create a slightly raised border around the circumference of the hole to ensure water is held within this zone and not funneled away from the tree. In the first few years after planting, trees must be watered. Ensure that the root ball does not dry out and keep in mind that a tree may need to be watered regularly, even when the weather is damp. If there is a long dry spell, trees with roots that grow slowly may dry out, even in the third or fourth year after planting.
Anchoring
It is important to anchor a newly planted tree. The new roots have to be able to develop undisturbed and movement due to wind can damage new roots. 
Traditional anchoring systems like double staking have always been, and continue to be extremely successful. If you choose to stake the trees, it is important to use a broad binding that will not strangle the tree. Please remember that the tree stem will thicken in the second year and the binding will therefore have to expand with the stem.

Question 5

How and when to prune young trees?

Accepted Answer

Pruning of deciduous trees (those that lose their leaves in winter) is often best carried out in winter, as it is easier to see the branch structure. Pruning of evergreen trees is often carried out in April, as they come into growth.
 
Exceptions to these rules include tender deciduous trees, best pruned in spring, once the risk of frost has passed, and also stone fruit trees (cherries, flowering cherries, apricots, peaches, plums and nectarines). These can be pruned in winter while young, but are later best pruned in summer. They can be at risk of catching the diseases silver leaf and bacterial canker if large branches, those thicker than your wrist, are pruned in autumn or winter.
How to carry out formative pruning of trees
 
Most ornamental trees are trained in a central-leader standard, with a clear trunk and a head, or canopy, of branches.
 
Forming a central-leader standard tree
Young trees can be trained to grow as standards with a 1-2m (3¼-6½ft) trunk.
Where trees grow with a clear central-leading branch that grows upwards ahead of the other branches, it is important not to cut this central leader, as this could spoil the final shape of the tree.
 
Year one
Remove all side branches from the lower third of the main stem
Shorten by half all the sideshoots on the middle third of the main stem
Leave the sideshoots on the top third of the main stem unpruned, apart from the removal of dead, diseased or damaged growth.
Cut to outward facing buds, so that the resulting growth extends outwards rather than into the centre of the tree
Year two
Remove completely the sideshoots that were shortened by half in year one (which should be now be in the lower third of the tree)
Shorten by half the sideshoots on the middle third of the tree
Remove any crossing or misplaced branches in the upper third of the tree
Year three
Follow the same steps as for year two.
 
Years four and five
Clear the trunk of side branches to the height desired
Continue to remove any crossing, dead, diseased or misplaced branches from the canopy.
Growing a central-leader standard as a branched-head standard to control its size
Some trees, oaks for example, develop as central-leader standards while they are young, but then lose their leader naturally after a number of years, and develop as branched-head standards.
 
It is possible to reduce the final height of trees that would otherwise grow as central-leader standards by removing the leader and pruning as a branched-head standard.
It is advisable to check in a book first as to whether this technique is suitable for the tree in question, as some trees can be spoiled in shape by premature removal of the leader.
 
Years one to three
Follow the steps above as for a central-leader standard.
 
Year four
Remove the leading shoot, cutting to an uppermost strong sideshoot
Leave three or four sideshoots in the top third of the tree unpruned to form the branches of the branched-head canopy. Only remove any badly placed branches or those that are crossing or rubbing
Shorten the sideshoots on the middle third of the tree by two-thirds, leaving stubs that can form replacement branches if needed
Remove all sideshoots from the lower third of the tree, to start creating a clear trunk
Year five
Remove any strongly upward-growing branches that threaten to dominate the canopy
Remove any crossing or rubbing branches
Shorten the canopy branches and sideshoots a little to balance the shape. Cut to an outward facing bud to encourage open growth
Clear the desired height of trunk of any growth. If new growth is stimulated from the trunk by this pruning, rub off the shoots as soon as they emerge
Problems
Where upright shoots threaten to compete with the leader of a central-leader standard tree, then a single leading shoot will have to be selected, and the others removed. Choose one that is upright and in line with rest of the tree.
Where the leader is broken by wind, snow or accidental damage, then cut it back to a strong side shoot that is growing fairly vertically. Attach a cane to this side shoot and tie the shoot in to the cane as it extends, training it upwards as a new leader.
 
Ref: RHS, 2021

Question 6

Identifying Tree Diseases

Accepted Answer

What are the most common Tree Diseases?
Trees, like any other living thing, are susceptible to diseases.  Some of the diseases encountered in trees are merely unsightly whereas others can reduce productivity or even kill the tree. For a previously healthy growing tree, stress often is the compromising factor which reduces plant defences and enables infection.
Foliage Diseases in Trees
Most of the common foliar diseases are fungal. Treatment, or lack of it, must be based on the threat presented by the disease compared to the cost of treatment; therefore, careful attention must be paid to disease identification.  Be aware that chemical injury and insects can mimic some of these diseases. Prevalence of foliar disease often is influenced by weather, so in large scale plantations, little can be done to prevent or treat the disease. The most practical control for some of these diseases is to simply rake and destroy leaves, the source of next year's infection, in the autumn.
Pine Needle Diseases Needle Blights
Needle blights primarily grow inside the needle and cause part of it to die.
Treatment of these needle diseases must be based on the particular disease, the size of the tree involved, and the setting. Most of the needle diseases are merely unsightly and pose no long-term threat to the tree’s survival. In those cases, no treatment is necessary unless the disease reduces the trees immediate merchantability. Some trees are large enough that tree size alone limits treatment options. Ornamental trees and Christmas trees have a much greater value than forest trees and may warrant a greater investment in disease treatment.
Hardwood Leaf Diseases
There are many foliar diseases of hardwood trees, but chemical injury and insects can mimic some of these diseases. Foliar disease often is a function of weather and little can be done to prevent or treat the disease. The most practical control for some of these diseases is to simply rake and destroy leaves, the source of next year's infection, in the fall.
Anthracnose
Anthracnose is a fungal disease that affects primarily the leaves but also sometimes the stems of hardwood trees. Severe damage can occur but there is very little that can be done to minimize the damage. The most common symptom of these diseases is dead areas or blotches on the leaves. Because of the scorched appearance of the leaves, the diseases are sometimes called leaf blight. Sycamore, dogwood, maple, hickory, walnut, birch, oak, and ash are susceptible.
Rust
Rusts are fungal diseases that affect leaves of several hardwood species. Leaf rust is a common problem, but rarely is serious. It is characterized by yellow spots on the upper leaf surface. Close examination reveals small yellow-orange bumps filled with powdery spores on the leaves. As with leaf spot, rust infestations will become apparent in mid to late August. The biggest effect on trees is early defoliation that would affect growth. Poplars and cottonwoods are susceptible to Melampsora rust and improved varieties have been bred for resistance. Most rust fungi have alternative hosts during the life cycle. Rusts affect cottonwood, poplars, willows, oaks, ash, birch, maples, and plums.
Leaf Spots
Leaf spots on trees are generally not important in the scheme of things but can be unsightly. Several species of fungi may cause leaf spot. The most common are Septoria, Phyllosticta, Mycoshaerella, and Actinopelte. These spots are generally brown and often the fruiting bodies may be seen on the leaves. Some leaf spots are caused by a parasitic alga (Cephaleuros virescens).  Cool wet springs are conducive to the formation of leaf spots. Septoria can also infect the stems of hybrid poplars forming a canker.
Tar Spot
Tar spot on maple and sycamore is not actually "tar" on the leaves, but rather a fungal disease. These diseases seldom are detrimental to the overall health of infected trees. Tar spots may cause premature defoliation but are not known to kill trees. Tar spots on maples are caused by fungi in the genus Rhytisma. The most common species are Rhytisma acerinum and R. punctatum.
Symptoms first appear in late spring or early summer as infected leaves develop light green or yellow-green spots. During mid to late summer, black tar-like raised structures are formed on the upper surface of leaves within the yellow spots. The R. acerinum fungus causes spots that are 1/4 to 3/4 inch in diameter, R. punctatum causes spots that are smaller (about a 1/16 inch diameter). Spots caused by R. punctatum are sometimes called speckled tar spots. 
Powdery Mildew
Powdery mildew is one of the most common plant diseases and is easily recognized. White spots or patches with a talcum powder appearance characterize this disease. Powdery mildews are severe in warm, dry weather with succulent tissue being more susceptible to infection. Many plants have developed a resistance to powdery mildew, but chemical treatments are effective control when the disease crops up. Most powdery mildew fungi attacking trees belong to the genus Microsphaea. The fungus overwinters in the leaves and is moved to the host plants the following spring by insects, wind, or rain.
Leaf Blister
Oak leaf blister is caused by the fungus Taphrina caerulescens and occurs on most species of oaks. The spots on the leaves are ¼ to ½ inch diameter and turn a light green as the young leaves expand. The spots age and become covered with an off-white coating of fungal growth that later turns brown. Leaves will remain on the tree. Cool moist conditions during leaf development are required and the leaf can only be infected during leaf expansion. Dormant spores overwinter in the buds of susceptible trees. This disease is of little consequence to the tree.
Ref: Arkansas University 2020

Question 7

What is the tallest tree species?

Accepted Answer

The Giant Sequoia is the largest tree species recorded to date. 
 
Hyperion: 380.3 feet (115.92 meters) is the tallest of all trees. This remarkable coast redwood (Sequoia sempervirens) was discovered in 2006 and is so tall that its top cannot be seen. Living in a secret location in Redwood National Park, California, it lives among other notable specimens including Helios at 374.3 feet (114.1 meters), Icarus at 371.2 feet (113.1 meters) and Daedalus at 363.4 feet (110.8 meters).

Question 8

What are the best trees for avenue plantations?

Accepted Answer

Trees planted to line an avenue, traditionally a straight path or road with trees running along each side, is a customary way to emphasise the coming to or arrival at a landscape or architectural feature. Avenues of trees are some of the most strikingly important structural plantings to be found in designed landscapes. Some of the species listed below are good examples of avenue trees:
 
- Carpinus betulus - Hornbeam
- Fagus sylvatica - Beech
- Liquidambar styraciflua - Sweet Gum
- Platanus hispanica - London Plane
- Sorbus Aucuparia - Rowan
- Taxus baccata - English Yew
- Tilia - Lime

Question 9

What are the most common tree insect pests?

Accepted Answer

The insect pests you are likely to encounter depend largely on the species of the tree. Aphids are a common pest of 'sappy' trees such as birch and beech. Spider mites can affect species such as walnut causing distortions on leaves and leaf miners in horse chestnut is a regular sighting. If you have a particular issue you are unsure of, feel free to send an email with an attached photo for the nursery to have a look at.

Question 10

What causes stress in trees?

Accepted Answer

Many environmental factors can cause a tree to be stressed. 
Drought, overcrowding, and damage to stem or roots are the most common causes. 
Physical stem damage via animal grazing or human interference invites infection by creating points of entry for pathogens. 
Root damage creates points of entry for pathogens and reduces the trees ability to collect water which puts the tree under stress, thus making it more susceptible to infection. 
Drought, whether from lack of rainfall, from overcrowding, or from root damage; reduces the ability of a tree to isolate infections and prevent their spread through the tree. 
Good tree management reduces drought stress and mechanical damage and thus reduces the likelihood of disease problems with trees.

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