Black Pine Basics – Pinus species
Black pines are popular as bonsai but they are more complex to care for than junipers or deciduous trees, like maple or elm. Most pines only have a single “flush” of growth each year so pines take longer to recover from mistakes. If you’re new to bonsai we recommend waiting until you have more experience. Once you have had a couple of years experience pines can be very satisfying to work on.
Black and White Pines
The two most common types of pines used in bonsai are Black pine and White pine. It is easy to distinguish between the two varieties by looking at the number of needles within each sheath – the short, light gray wrapper at the base of the cluster of needles. Black pines have two needles per sheath vs. five needles for a white pine. Black pine needles are bright grass green in color vs. slightly blue-green for white pines. White pine needles are usually soft if you press against the tip of the needle. Black pine needles start off soft in spring and become very sharp in summer.
When grown as a landscape plant the needles of either tree may be 4 inches long. On a bonsai we usually want them to be 1 inch or less. We’ll describe techniques that will shorten branches and needles.
Other Two Needle Pines
These are less commonly used as bonsai, but occasionally you see one of these varieties. Here’s how to distinguish them:
- Red Pines – needles are the same color as black pines but are only 1/3-1/2 the thickness of a black pine needle. The needles are also softer and more flexible
- Cork Bark Black Pines – this variation has very thick bark that looks like “wings” running up and down the trunk. These pines are much weaker than regular black pines and must be handled more delicately
- Mugo or Swiss Mountain Pines – needles are the same color as black pines but aren’t as sharp or as long
- Monterey Pines – needles are the same color as black pines but are soft and springy all year round.
- Scotch Pines – needles are blue-green and trunks often have flaking orange bark.
- Bristle Cone Pines – identified by the specks of white pitch scattered all over the needles. The needles are often curved
- Shore Pine, Lodge Pole Pine and other native pines are occasionally used in bonsai and have their own peculiar maintenance requirements.
Single Flush Pines vs. Dual Flush Pines
Recently bonsai people have been categorizing pines as single flush or dual flush. What does that mean and how does it affect how you work on pines?
Basically single flush fines have one flush of growth every year. Double flush pines also produce one flush per year, but can be stimulated to produce a second annual flush of growth. Japanese Black and Red pines are the most common examples of dual flush pines. During the Refinement Phase, when we are growing more compact branches we can speed up the development process if the tree can produce a second set of candles (new growth) instead of just one. That second set of candles will be shorter – helping us meet our goal of compact growth. And rather than a single candle we usually get multiple meaning we have more branches to use.
This distinction between single and dual flush only matters during Spring while Controlling Growth.
Basic Pine Care
The tasks described below apply to all pines.
When to Repot
Pines that need to be repotted and are very healthy can be repotted before candles come out, generally mid-March to early-April. Repotting causes pines, and all plants, to restart their “clock” and will act as though it is the beginning of growing seasons.
How do you know that your pine needs to be repotted this year? Younger trees grow faster than older trees so you may need to repot every year or two initially, but only ever three to five years after the tree is mature. Here’s a couple of easy ways to tell if it’s time.
- Is it difficult to push a chopstick into the top of the soil?
- Is the plant pushing itself up out of the pot?
- Are roots coming out the bottom drain holes?
It’s important that you don’t do much pruning of green needles / branches while repotting. Because pines are evergreen they produce sugar year round and don’t store it in their roots during dormant season like a maple or other deciduous trees. If you prune away green growth at the same time you repot you are depriving your tree of the ability to recover as quickly. And if you remove too much you may even kill the tree.
Any significant pruning should take place in autumn. See Autumn section later.
Black pines use the conifer mix described in the Soil Basics page. We recommend adding 1-2 tablespoons bone meal to the soil when repotting. These spur root growth in newly potted trees. It is also important to collect some mycorrhiza from the old potting soil and include it to the new soil. See Mycorrhiza Basics for more information.
Fertilizing Black Pines
All trees need fertilizer all year round. It supplies nutrients not found in bonsai soil which is mostly inert. New growth needs nitrogen, so we recommend a high nitrogen fertilizer be applied beginning in late-February or early-March. The easiest to use is Osmocote 19-6-12 — timed release fertilizer pellets. Because these don’t release fertilizer from the resin coated pellets until the weather is warmer, we also recommend applying a liquid fertilizer like Miracid at quarter strength every week or two .
|Pot Size||How Much Osmocote to Use|
|Small (e.g. 4″ diameter)||2-3 teaspoons|
|Medium (e.g. 12″diameter)||2-4 tablespoons|
|Large (> 12″ diameter)||4-8 tablespoons|
Also, we’ve found the Osmocote releases at different rates depending on the temperature. When the weather is hot, e.g. more than 90-degrees, it releases very quickly we recommend removing half or more of the Osmocote from the top of your soil.
The Osmocote package says that it is good for about 6 months, but in reality it doesn’t last more than a couple of months when used on bonsai because we water so frequently. You’ll need to need to replenish it every couple of months.
In November remove all high nitrogen fertilizer pellets and replace with low nitrogen variety, 0-10-10.
Removing Cones and Pollen Sacs
Not long after the candles appear pine cones and pollen sacs may appear, growing at the base of the candle.
Pines don’t produce flowers but they produce seeds located inside the female pine cones and male pollen sacs that open to release pollen that will float with the wind to fertilize nearby cones. The female cones are generally located near the top of the tree but the pollen sacs are usually lower – reducing the chance of self-pollination. There may be just a few pollen sacs or more than a dozen. Producing cones or pollen takes energy and so we remove both. You may cut them off using sharp scissors, or gently twist them off.
Everyone knows what a full sized pine cone looks like, but not everyone knows what a young one looks like. Or what a pollen sac looks like.
Controlling New Growth
All bonsai begin in what we call Development Phase. During this phase the focus is on developing a good size trunk with good taper and the lower part of the trunk flaring out to meet the roots. This is also the time to develop good surface roots. To accomplish this the tree will be allowed to grow wild (a bit) and bulk up. Later in this phase the focus is on removing branches that are in the wrong place and fatting up the ones you want to use. Only then will you use the following techniques to refine branches.
For a more complete description of Development vs Refinement Phases see Bonsai Lifecycle.
Trees in Development Phase should be left alone – except for minor pruning to remove small branches you know you won’t use, like branches coming out of the bottom of a branch or growing within the crotch of two branches. Do not do the steps described in the next section – Breaking Candles to Control Growth.
Breaking Candles to Control Growth
These instructions only apply to trees that are in Refinement Phase.
Generally sometime in March to April pines grow new foliage. It begins with what we call a candle. This green stalk grows longer over a couple of weeks. It looks a bit like a skinny stalk of asparagus. After a few days later bumps appear on the surface and after a few more days those turn into needles. Needles take a couple more weeks to grow to their full length.
Our goal is to keep branches short enough that they look in scale to the tree’s height. We also want to shorten the needles so they fit the scale of the tree. Because each new candle becomes a branch next year we need to short candles this year. Most new candles will be longer than we wan but there are ways to shorten this year’s candle before it becomes next year’s branch. On any species of pine you can break the candle. This is done in spring before needles have emerged – just after Stage 1 of Candle Development shown above.
Candles can vary a lot in in length. Some may be 1 to 2-inches, some may be 6-inches+, and some will only be 1/4-inch. The shortest candles should be left alone. Longer candles should be broken so that they are similar in length to the 1 to 2-inch candles. To break a candle grasp with the tips of your fingers and pinch until the candle breaks. You may want to wear gloves because you will get sap on your fingers.
After a short time the sap on the top of the candle will dry out and Stages 2 and 3 of Candle Development will occur.
If you have a Black or Red Pine, both Dual Flush Pines, there is an alternative method that may be applied. It’s a bit complicated so not described here. See De-Candling Dual Flush Pines at end of article for details.
Warm weather, up to 90 degrees, is great for black and most pine trees. But over 90 degrees and there is a risk of drying out and sun burn. Move your trees where they’ll get full sun in the morning but filtered sun after noon. If this isn’t practical consider using shade cloth. Pines that are native to mountains, such as white pines, may do better with less heat.
Red spider mites are a problem for pines when the heat gets too high. Keeping trees well watered should minimize infestation. You may need to spray. See Pest and Fungus Control Basics for more details. There are also some Pine-specific Pest Control you may need to follow.
During Refinement Phase the focus is on removing branches that are in the wrong place and fatting up the ones you want to use.
Like other bonsai, pine branches should look like a diamond or arrow shape when viewed from above. Branches coming out of the trunk are primary branches. We want to develop these so that they taper from larger (at the trunk) to small (near the tip). To do this we develop larger secondary branches near the trunk and smaller ones near the tip. We may also substitute a secondary branch and make it become the end of the primary.
Secondary branches, aka lateral branches, should alternate from side-to-side and not be directly across from each other, aka bar-branches.
To achieve a shape like this we need to be able to control the number and size of each branchlet – both the diameter and length. For pine trees that means slowing down the growth on each branch when it is at the correct size. The basic way we do this is to control how long each new branch will be via pruning and removing unnecessary branches.
You should not be pruning your tree if the trunk is still being developed. Let the tree grow instead.
Previously we were recommending pruning around June, but we now know that pruning in June results in longer growth and fewer buds developing than if we prune later. We went more buds so now we recommend pruning in late autumn to early winter.
Remove Old Needles
Because buds are easy to break off we recommend any fine wiring be done after buds have emerged as candles. Remove wire before new buds appear in late-summer to early-autumn
After the weather has turned cool it is time to remove old needles – early-December is a good time. Pines can hold their needles for three or four years, but it is important to remove older ones for a couple of reasons.
- Old needles are more susceptible to attack by fungus. Rain and overhead watering can spread the fungus to new needles
- Excessive needles reduce sunlight and air flow inside the tree.
By removing needles we are promoting extra sunlight inside the tree. This can help buds which haven’t opened yet to do so next year. Also, extra airflow can help reduce fungus growth.
Begin by removing “old” needles – those from last year’s growth. These often are yellow in color. Next you’ll remove “extra” needles to help balance growth.
How Many Pairs of Needles To Keep
Because pines grow more vigorously at the top of the plant and on the ends of the branches, we balance the growth by leaving different numbers of needles on different parts of the tree. So, while thinning needles remove more needles at the top than the bottom.
Here’s a good rule of thumb — for very healthy trees.
After thinning, your tree should have –
- 8-10 needle pairs on the bottom of the tree
- 6-8 needle pairs in the middle of the tree
- 4-5 needle pairs at the top of the tree
- For branches that are closer to the trunk (and so get less sunlight) leave an additional 2-3 pairs of needles.
How to Remove Needles
For many years we’ve recommended pulling needles one-by-one, leaving the sheath – the gray covering that is found at the base of the needle pairs. The exception was on Cork Bark Black Pines which are more fragile. Pulling needles were more likely to pull the sheath off the branch and so we recommended cute just above the sheath. Now we’re changing our recommendation – cut needles on all types of pines. It’s easier, often faster – and seems to result in more buds later. Tweezers can be used to move adjacent needles out of the way so you can more easily cut the needles.
If you decide to pull needles, it is important to pull one needle at a time to minimize damage to the bark and any buds that may be hidden. This is easier if you use tweezers, especially deep inside a tree.
In January take a look at your plant again. You may want to remove a couple more pairs of needles on branches that look like they are growing more rapidly than the others.
Wiring & Pruning
The best time to do major pruning and wiring is between November and January. It will be easier to do if you have thinned needles first.
The wood in pine trees are very springy, so if you are making major bends the wire will need to remain on for 3 to 6 months. In that time the tree may grow substantially so it’s important not to wire too tightly. Check your wiring in March to see that it isn’t causing damage to the bark.
De-Candling Dual Flush Pines
The following technique may be used to get even shorter candles than by breaking them. However, this is only applicable to very healthy dual flush pines – black and red pines. Single flush pines don’t have the energy to grow two sets of candles in a year and you may kill the entire branch if you use this technique on those pines..
Cutting the candle will force new buds to form at the base of the old candle. These will turn into more than one candle – so more options for us to produce fine branching. And they will be shorter than the original candle.
When to Cut Candles
Cut this year’s new candles as soon as the candle is open and needles on the candle are fully pen and spread – Stage 3 of Candle Development in the figure above. In the Palo Alto area this is typically between mid-June to early-July depending on the weather that year. Once the candles are fully open you have about 3 weeks to complete your pruning. But there are a couple more things you should check first:
- Only cut candles if the needles are bright green and free of insects
- Candle must still be green. If it’s starting to turn light brown / gray, you’ve waited too late. You’ll have to wait until next year.
- Only if the tree is strong. Weak trees should only have candles cut every other year
We recommend cutting all candles at the same time – but to vary the length of the stub being left. Specifically, we want the stub length to vary according to the size of the candle and its location on the tree. Here’s how this works and why we care. Stubs that are different lengths die back at different rates. Longer stubs will take longer to die back which means that when new buds form at the base of the candle they will start growing (aka “pushing”) several days later than on shorter stubs. As a result, the new candles will be more nearly the same size.
How to Cut Candles
Your scissors should be extra sharp for a clean cut. Make sure that you make your cuts perpendicular — cutting a candle on a slant means dormant buds at the base will get an uneven start.
Pine trees grow more strongly at the top of the tree, so candles at the top will always be longer than the candles at the bottom of the tree. Candles on the tips of the branches receive more sun than candles closer to the trunk and be stronger than those that are partially shaded. By adjusting the size of the stub left after cutting we can slow down stronger candles and allow weaker ones to become stronger – resulting in more balanced growth.
Candles that are already very small (e.g. 1/4-inch long or hidden inside the tree) shouldn’t be cut. Leave them alone.
Cut candles on upper branches so that the stub remaining is between 1 to 1.5 times as long as the diameter of the candle.
Cut candles on middle branches so that the remaining stub is about the same as the diameter of the candle.
Lower Branches and “Inside” The Tree
Cut candles on Lower branches so that the remains stub is about 1/2 the diameter of the candle. Do the same for candles that are “inside” the tree (partially shaded).
Choosing Buds for Future Branches
Two weeks after you’ve cut candles you should see new buds growing at the base of the shortest stubs. Candles will begin growing a bit later at the base of longer stubs – that’s by design. This gives a head-start to new candles on parts of the tree that were weak.
The next phase of work is to identify which buds you want to develop into new candles. There may be several new buds, but you’ll remove all unneeded buds. Here’s how to choose which to keep and which to cut off.
Because you want two branches that are “opposite” each other you might choose to keep the buds shown to the right. But it’s a bit more complicated than that.
The goal is to have two horizontal branches, so if there are more than two buds you’d pick two and remove the rest. There are a few cases to consider. Look at the figure below. In this case the ones on the top left and right are the obvious choice to keep.
But, you want the new branches to be of equal strength. On this tree the two largest buds are on the bottom. The branch could be rotated by wiring it at this stage it is easy to break off buds. Better to wait a few months to let the buds turn into new candles and become stronger. If the strong buds were on opposite sides of the branch we’d use them, but in this case it makes sense to remove them.
Now look at what’s left. We’ve still have two buds that are opposite each other and similar size so we’ll use those and remove the remaining one. Each candle is different but hopefully these examples will help you decide how to choose the buds to use and the ones to remove.