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Douglas Fir Bonsai Fundamentals
Douglas fir (Pseudotsuga menziesii) is a tree species native to North America. It has fantastic features for bonsai and very old specimens can be found in the wild as yamadori. There are some timings and techniques that are unique to Douglas Fir bonsai, so in this guide, we'll take you through everything you need to know.
- Pseudotsuga menziesii
- Pests and disease
- Position in the garden
Pseudotsuga menziesii is a very interesting species of evergreen conifer that possesses many characteristics suited to bonsai cultivation.
Mature trees have very rugged, flaking bark that gives a strong appearance of age, and their small, compact foliage can add to the sense of scale in a bonsai composition.
Douglas fir have a very long lifespan and commonly live for hundreds of years. They gain their rugged appearance with age, but you will find that younger plants have a thin bark that is smooth and grey. This will change as the tree ages.
Pseudotsuga menziesii grow their branches in response to sun exposure. If you travel to see them in their natural forests you'll notice their lower branches have been shed and growth is focused at the top of the tree where it has grown clear of surrounding trees. This is important to take note of if you want your tree to reflect the natural environment, but equally, if you want lower branches on your tree they will grow just fine if given enough sunlight.
When pruning a Douglas Fir, timing is very important. Not only do they go into dormancy earlier than other conifers, but there are particular considerations around buds that are produced on new growth.
Pruning earlier in the growing season triggers these buds to mature, which allows them to produce new growth the following season. If pruning occurs too late, new buds won't mature and you will need to wait an extra year for these to produce growth.
Initial styling and branch selection
The best time to do major structural pruning on a Douglas Fir bonsai is in early spring before new growth has appeared. This is the best time to remove primary branches and create deadwood, as well as to perform secondary pruning.
The tree will have an abundance of stored energy from the last growing season that it will invest in new growth, so pruning now helps the tree to allocate resources to the remaining branches and start the healing process on new wounds.
Secondary pruning and refinement pruning
As with setting primary structure, secondary and refinement pruning should start in early spring before growth has started. The secondary structure of your bonsai should be pruned and wired to set the tree up for the growing season. The shape of the bonsai should be maintained and branches should be pruned back to the desired silhouette of the tree.
Branches should be pruned and wired in such a way to allow good light penetration to each branch.
After the first spring pruning, the tree should be left to grow. Once new growth has hardened off, it is time to prune again. You can tell that growth has hardened off when leaves turn a deeper green color and develop a waxy coating.
During post-hardening pruning, you should trim back growth to maintain the shape of your bonsai. As with other species such as Larch, Douglas Fir need to be pruned back to a bud.
Pruning back to juvenile buds over late spring and early summer triggers a response in the tree that causes these buds to mature. If you wait until late summer or early autumn to prune, these buds are unlikely to mature until the next growing season.
Wiring a Douglas Fir bonsai is best done in early spring, as part of an overall styling before new growth has started to push out. This allows the tree the best opportunity to batch any damage caused by wire application or bending.
Late summer or early autumn can also be an ok time to wire Douglas Fir, but be aware that if you are also pruning as part of an overall styling you will probably miss out on triggering juvenile buds to become mature.
Copper wire is generally the best choice with Douglas Fir as it gives a stronger hold than aluminum and generally will be better disguised against the branches as it weathers. Copper wire 'work hardens', meaning it hardens more as you bend it. This is what gives it such a good holding capacity for bonsai.
Aluminum wire can also be used when styling a Douglas Fir bonsai, but you will need a bigger gauge of wire to achieve the same bends you would with copper. Aluminum does have the advantage of being softer, which means it is easier to apply if you are a beginner or do not have the hand strength to use thick copper wire.
Wire should be applied at a 45°-60° as you wrap it around the branches. It should be wrapped in the same direction you want to bend the branch. This will mean the wire stretches as you bend the branch which will support the bend and give a better hold.
Douglas Fir has a very rugged bark, which means wire should be left in place until it has started showing signs of biting into the branch. This means the branch has produced enough new growth in the new position to hold it there, and the branch will not suffer any long-term scarring as the bark will quickly grow over and disguise wire marks within a season or two.
Watering your bonsai well is essential for maintaining good root health and the overall well-being of the tree. Douglas Fir can be somewhat challenging when watering, but in general they benefit from being allowed to dry out slightly.
Your bonsai should be watered when it needs it, not on a schedule. Generally this means when the top quarter to half inch of soil dries out, but it depends on the tree, your environment and when you'll next be able to water the tree.
Douglas Fir can sometimes be quite sensitive with their roots, so repotting and root care, in general, is very important for this species.
When to repot Douglas Fir bonsai
Douglas fir bonsai should be repotted in late winter or early spring. The best time to repot is just as buds are swelling for spring growth. Summer repotting should be avoided, as it risks the health of the tree.
When deciding whether your bonsai needs to be repotted, think about the following:
- It needs a style change, such as a change of angle, a change of front, or a different container
- Water can't percolate through the soil, making watering challenging
- Soil has started to decompose or rot, leaving the root system too wet
If your tree meets any of the above criteria, then you should repot it at the next repotting window.
Due to the shallow nature of most bonsai pots, a modern soil substrate is essential to create the best environment for your tree to thrive. Modern bonsai substrates have components that are aggregate and allow water to drain freely through the soil.
There are many popular components and mixes, and the ideal substrate will depend on both your environment and your ability to water throughout the day. A specialist bonsai nursery should be able to advise you on good options for your area.
If you like to make your soil mixes, akadama, pumice, and lava are 3 very popular choices. I use these in a 1:1:1 ratio for my Douglas Fir bonsai and most of my other conifers.
Akadama has a small amount of organic matter that will hold nutrients for your tree to use after fertilization. It also has a special internal structure that makes it ideal for creating a finely ramified root system.
The pumice and lava are both great for maintaining aeration in the soil system to encourage root growth. Pumice is also particularly good at holding water in a way that makes it available for roots.
As an evergreen conifer, Douglas Firs are usually potted in unglazed ceramic containers. The shape will depend on the style of the bonsai, but a shallow oval is a good choice for most styles.
If you are using a circular pot it's a good idea to pair it with a tree that has a lot of movement, ideally one where the apex breaks the lateral boundary of the pot. This adds to the interest of the composition.
With their rugged appearance, Douglas Fir can also look great on rocks or slabs.
How to repot Douglas Fir bonsai
The key to success when repotting a bonsai tree is to be methodical and precise. You must always leave a portion of the root ball untouched so it can start to rebuild the rest of the root system, so make sure the roots you are removing are ones you don't need.
Here are the steps I go through when repotting my Doug Firs:
- Using a root sickle, free up 50% (at least) of the root ball from the sides of the pot. Even though it has a serrated blade, this tool is designed to be used in a scraping motion, not a sawing motion. Scrape the soil and roots away from the sides of the pot to help you get the root ball out.
- Cut the tie-down wires that are holding your tree in place and remove the bonsai from the pot. When pulling the bonsai out the tree and the root ball must move together. You don't want to tear roots and rip the tree out of the root ball. If the tree isn't coming, go back to the root sickle to free up more of the root ball.
- Remove the moss from the top of the soil mass. You can peel this off with your hands, use a paint scraper to bring it off in chunks, or use a chopstick. This moss should be kept aside to be dried and ground up for use as top dressing.
- Start scraping away soil from the top of the root ball. You have two aims here. First, expose the nebari and improve the base of your tree. Secondly, remove compacted soil to find intact soil particles underneath. This is vital to improve air and water flow in the root ball.
- Turn the bonsai on its side to reveal the bottom of the root ball. You may want to use a prop if the tree is heavy. You should now be able to remove the matted roots on the underside of the bonsai using a paint scraper.
- Reduce the height of the root mass using a chopstick to scrape away the soil. Try to identify any areas of decomposed soil. These can be a source of health issues in your Douglas Fir and need to be replaced with an aggregate soil mix. Decomposed soil is black and wet and can sometimes have a sour smell.
- The sides of the root ball can now be addressed. Cut away the matted roots that encircle the root ball and reduce the sides of the root ball as required. Doing this can make the root ball very unstable in a bonsai with a weakened root system, so the tree should be moved around as little as possible after this step.
- Start preparing the bonsai container. Firstly, add some screens to the drainage holes to prevent soil from escaping. Next work out where your tie-down wires need to be and put them into position. Tying the tree securely in the pot is an extremely important part of the repotting process and one of the biggest factors in the long-term success of your bonsai. Roots will not grow if the tree is mobile in the pot, so use 2 or three wires to tie the bonsai into place and keep it rock solid.
- Add soil to the pot with a light layer across the bottom of the pot and a larger mound of soil in the center. Place your bonsai on top of the soil mound and gently rock it from side to side and forwards and backwards to work the soil into gaps in the root ball. Once the tree is settled into place, make sure you are happy with the front and planting angle, then secure it in place with your tie-down wires. Finally, fill the rest of the pot with soil.
- Using a chopstick, introduce soil into any holes in the root ball you may have created by removing old soil. You should aim to fill all gaps in the root ball. It helps to take note of where these gaps are before securing the tree in the pot. Sometimes it can also help to mark them with wire or sticks.
- Prepare a topdressing for your bonsai by grinding up a 1:1 mix of some dried sphagnum moss and locally collected green moss. Apply a thin layer over the root mass, then mist it with water using a spray bottle. When wet the topdressing will hold in place for proper watering (trust me, it's crazy how this works but it does). This topdressing will grow into a proper layer of moss over the next few months, which helps to promote root growth, better maintain water balance, and protect the soil from passive decomposition from watering.
- As your final step, give your bonsai a very thorough watering. There will be some small particles of broken soil from chopsticking in the pot, so we need to wash those out. Keep watering until it is clear when running out of the pot.
The aftercare following a repot of a bonsai tree is vital for the health of the plant. Douglas Fir is particularly fussy when it comes to watering, so aftercare of this species is very important.
When we repot a bonsai, we have to prune roots. The wounds on these severed roots can do two things based on their environment. They can callus and heal, or they can die back and rot. We want roots to heal and be the source of new root growth, so we need to provide the right conditions for roots to do that.
The best way to get wounded roots to heal is by giving them an oxygen-rich environment. High amounts of oxygen will also stimulate new root growth, which will help to build your bonsai. On the other hand, if you water your bonsai too much after a repot roots will not heal well.
In real-world terms, this means you need to make sure your tree is drying out a little between each watering. For day-to-day watering, I'd recommend letting the first half inch of soil dry out as a sign you need to water again, but after a repot you should let the pot dry out a little bit more following the first watering. I'd let the first inch of soil dry out before you water again, to give the roots the best opportunity to heal and trigger new root growth.
Another consideration with aftercare is where you place the tree in your garden. By removing roots you reduce the tree's capacity to move water, so it will need protection from elements that require lots of water movement, namely wind, and sun.
Your bonsai should be placed somewhere to allow it morning sun and afternoon shade for the first few weeks after a repot. Make sure it is sheltered from the wind, keeping it off the bench and on the ground if you need to.
Ideally, your bonsai should also be sheltered from the rain after a repot to control water, but if that isn't possible consider propping the pot on an angle to improve water removal from the pot.
Fertilizer is a key ingredient in a healthy bonsai. It provides valuable nutrients and stimulates growth. How and when you fertilize depends on the stage of development and health of your bonsai.
Plants in early development should be fertilized heavily. This will help them to grow strong roots, build foliage, thicken the trunk and branches and heal major wounds.
Trees in secondary development should be fertilized moderately. The aim should be to stimulate growth to grow out branches where they are needed and hold back growth by pinching or pruning where the structure has already matured.
Douglas Fir bonsai in refinement do not need fertilization to stimulate growth, but they do need a good balance of micronutrients to keep them happy and healthy. This is where a very light application of balanced fertilizer across the growing season can be helpful.
Pests and disease
Douglas Fir trees can suffer from a disease-specific to their species named Swiss needle cast (SNC). This is caused by an organism named Nothophaeocryptopus gaeumannii and causes the loss of two and three-year-old needles. This reduces the photosynthetic area of the tree, which can significantly reduce its vigor. Unfortunately, infected needles can't be cured, but the use of an antifungal treatment can help to prevent further spread.
Doug Fir bonsai are also susceptible to common pests such as spider mites. These feed on the chlorophyll in the needles of the bonsai, which can cause greying of the foliage. As the disease progresses you will be able to see stippled yellowing and potentially fine webbing.
Spider mites can be treated with daily hosing of the foliage mass for 2 weeks, or failing that a miticide.
Position in the garden
Established Douglas Fir bonsai grow very well in full sun and can be grown outdoors all year round. Large and healthy trees can tolerate very high temperatures, although weaker bonsai may benefit from some protection from extreme heat.
As they are native to temperate zones, Douglas Fir can be overwintered outdoors. Weak or sick trees may need more protection, such as placing them in a cold frame or a greenhouse.