Black Pine Basics - Pinus species

Black pines often used as bonsai and our club have had a number of presentations about their care. The method of training and caring for black pines also applies for most other pines, so future articles on say white pine (aka five needle pine) will rely on this article for the basics and then discuss the differences.

Identifying Pines

White Pines have five needles per sheath and are usually softer than black or red pines. The needles often have a slightly blue color.

Black pines have two needles in a sheath as shown in figure 1. When grown as a landscape plant the needles may be 4 inches long. On a bonsai we usually want them to be 1 inch or less. New needles are bright green and somewhat springy to the touch. During the summer the needles will become harder and very sharp -- pressing your hand against the needles can be painful.

Other pines with two needles per sheath include:

Black Pine
Black Pine Needles

When to Repot

Pines should be repotted during late April or early May because you will create shorter needle growth.

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.

Black pines use the conifer mix described in the Soil Basics page. We also recommend adding 1/2-1 tablespoon of Super Phosphate and 1-2 tablespoons bone meal to the soil when repotting. These spur root growth.

Fertilizing Black Pines

Fertilizing is a topic of great discussion among bonsai people. There are those who say fertilizer cakes are best, or Osmocote, fish emulsion, Miracid, etc. Each has its advantages. The easiest for a beginner to use is Osmocote 19-6-12 -- timed release fertilizer pellets. You may also occasionally use Miracid at half strength.

We recommend fertilizing beginning in late-February or early-March. After candles are removed (see next section) additional fertilizer should be added.

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

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. So, you'll need to need to replenish it every couple of months.

Also, we've found the Osmocote releases at different rates depending on the temperature. When the weather is cool, e.g. less than 70-degrees, very little is released. And, when the weather is hot, e.g. more than 90-degrees, it releases very fast! So, when the temperatures get above 90-degrees we recommend removing half or more of the Osmocote from the top of your soil.

How to Produce Compact Growth

Our goal is to keep the distance between branches small and in scale to the tree and to shorten the needles so the tree looks more in scale.

Because the candle becomes the new branch and we want the length of branches to be short and compact, we need to make the candles short. Most new candles will be longer than we want. But, if we remove the first candle a new set of candles will grow. That means we will be replacing a single candle with multiple ones, and the new ones will be shorter.

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Figure 2 - New Buds

Cutting the candle will force new buds to form at the base of the old candle.

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 nearer to the trunk so they will also grow more strongly. Our goal is to have candles (and thus branches) that are nearly the same length, and the following technique helps us achieve that.

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 a two or 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 pine cone looks like, but not everyone knows what a pollen sac looks like.

Pollen sacs at base of candle
Figure 3 - Pollen sacs at base of candle - so many you can't really see the candle

When To Cut Candles

The time to cut back is as soon as the candle is open and needles on the candle are open and spread. In the Palo Alto area this is typically in late-June to early-July depending on the weather that year. See the figure below.

Stage 1 of Candle Development
Stage 1 of Candle Development
Stage 2 of Candle Development
Stage 2 of Candle Development
Stage 4 of Candle Development
Stage 3 of Candle Development
Figure 4 - Stages of Needle Growth

Once the needles are fully open, you will 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 for next year’s growth.
  • 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 the length of the stub being left will vary according to the size of the candle and according to its location on the tree. Here's why. Stubs that are different lengths die back at different rates. Longer stubs will take longer to die back, and so 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.

On top branches, or candles that are on the ends of the branch and receiving full sun, the stub should be 1 to 1.5 times as long as the diameter of the candle being cut.

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Figure 5 - Candles on Top Part of Tree

Candles located on branches in the middle of the tree would be cut so that the stubs are about the same as the diameter of the candle.

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Figure 6 - Candles on Mid-Tree

On bottom branches, or candles that are "inside" the tree (partially shaded) the stub should be 1/2 as long as the diameter of the candle being cut. (as on the right)

Candles that are already very small (e.g. hidden inside the tree) shouldn't be cut at all.

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Figure 7 - Candles on Lower Part of Tree

Your scissors should be extra sharp for a clean cut. Also, make sure that you make your cuts perpendicular -- cutting a candle on a slant means the dormant buds at the base will get an uneven start.

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Figure 8 - Keep Cuts Perpendicular

Choosing Buds for Future Branches

Two weeks after you've cut candles you should see new buds growing at the base of the candle. This photo shows three new buds

New Buds

New Bugs
Figure 9 - Identify new buds

There may be several new buds, but because you want to develop two horizontal branches you'll remove all unneeded buds.

Which buds should you remove? Because you want two branches that are "opposite" each other you might choose to keep the buds shown to the right. But its a bit more complicated than that.

Choose your buds
Figure 10 - Choose your buds

You will want the branches to be of equal strength. So, the first step is to remove the strongest or largest buds.

Remove the strongest buds
Figure 11 - Remove the strongest buds

Now you'll want to look at what's left.
If you have buds that are opposite each other and on a horizontal line you'll want to use those. You may need to twist the branch a bit with wire to make this work -- however putting wire on now is often tricky. Because you don't want to damage the new buds wait until fall.

Now, if there are buds on the bottom you'll remove those.
And, finally remove any extra buds.

Remove extra buds
Figure 12 - Remove "extra" buds

Thinning Needles

In December you should remove excess needles. Over the year your tree has probably gotten very full and as a result the inside of the tree is getting less sunlight than the outside. And growth on the top is getting more sunlight than the middle or bottom of the tree. Thus, we want to "thin" the needles.

We begin by removing "old" needles, those we may have missed from last year's growth. These will be yellow. On black pines we recommend using a pair of long tweezers to grasp each needle and pull gently. We want to leave the sheath - the gray covering that is found at the base of the needle pairs.

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.

How Many To Keep

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.
Thing needles according to their position on the tree
Figure 13 - Thin needles according to their position on the tree

When the needles are thick and tough to pull you you may want to cut them instead of pulling. Cutting is often easier and it reduces the chance that you will accidently remove any buds hidden inside the sheath. Simply cut the needles off just past the sheath.

Thing needles according to their position on the tree
Figure 14 - Cutting Needles
Thinning inside the tree
Figure 15 -Thinning inside the tree

Because Cork Bark Black Pines are more delicate and it is easier to damage the bud, we recommend cutting the needles off just above the sheath. Needles on white pines should also be cut. You can do this for all pines, but most people just pull the needles on black pines, red pines, etc. because it is faster. To minimize damage it is important to pull one needle at a time! This is easier if you use tweezers.

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.