The juniper bonsai or Japanese juniper makes for a beautiful evergreen coniferous tree, that when cared for properly, can be grown outdoors as well as indoors. While the Juniper Bonsai is known to live beyond 100 years old, knowing how to care for your Juniper Bonsai tree will help ensure that you’ll have your beautiful plant for decades to come.
How to care for a Juniper bonsai tree indoors? To care for a Juniper bonsai tree indoors, maintain moist soil, use well-draining bonsai soil, provide bright sunlight, keep temps between 10 and 86°F, and provide high humidity.
This guide to indoor juniper bonsai tree care will go over everything you need to know, from good watering habits to the type of soil the plant prefers as well as lighting, temperature, and humidity. I’ll even tell you how to train a juniper bonsai and when to prune it, so make sure you keep reading!
Juniper Bonsai Tree Care – All You Need to Know
The juniper bonsai is regarded as a hardy plant genus, of which there are upwards of 70 unique species.
Whether yours has scale-like or needle-like foliage, establishing a good care routine will allow your indoor tree to thrive.
Here’s what you need to know.
How Often to Water a Juniper Bonsai?
Juniper bonsai species appreciate moist soil that doesn’t cross the line into waterlogged territory.
Moist soil feels slightly wet. If you put your finger in it–which I recommend you do–your fingertip will come out feeling moist but without beads of water on it.
If the soil feels slushy, soggy, or soaked, then you’re watering the juniper bonsai too much.
Beginner indoor gardeners are especially susceptible to overwatering, which is the term for watering your plants too frequently.
The trouble with overwatering is that you could create the right conditions for fungal diseases such as root rot to develop. I’ll talk later about root rot, but it’s a very deadly plant disease.
Despite the moisture requirements of this plant genus, many juniper bonsai species need their soil to dry before you water them again.
Does the soil need to dry out between waterings? Yes, but not completely.
When you put your finger in the juniper bonsai’s soil and you don’t feel moisture, then it’s time to water your bonsai plant again.
You should never allow the juniper bonsai’s soil to dry out entirely. Your plant can become dehydrated.
The roots–if any were visible before–will now noticeably point out. The trunk can develop creases, but these can be small and thus easy to miss.
What’s more difficult to miss is the hard soil around the perimeter of your indoor tree. If the soil has no give when you put your finger into it, then you need to water the juniper bonsai more often.
How you water this plant matters. You’re supposed to water the juniper bonsai deeply to soak through to the root system.
You can water with a gardening can or even by using a garden hose on a light setting.
Water the juniper bonsai until the water exits through the drainage holes.
What Soil Does the Juniper Bonsai Need?
The best type of soil for the juniper bonsai is unsurprisingly bonsai soil.
If you’re unfamiliar with bonsai soil or what makes up bonsai soil, allow me to explain.
Bonsai soil is a type of substrate with ingredients like fine grit or gravel, organic potting compost, lava rock, pumice, and Akadama.
Let’s go over these ingredients one by one and talk about what they do.
The grit or gravel allows for the aerated, well-draining soil conditions that any healthy indoor juniper bonsai species needs.
That said, you can safely forego grit or gravel and use other amendments instead and still have a good, well-draining bonsai soil.
If you do opt to add grit or gravel to your bonsai pot, moderation is key. Overdoing it on either ingredient dries out the pot too much, necessitating more frequent watering that the juniper bonsai doesn’t really like.
Organic potting compost includes ingredients such as sand, perlite, and peat moss. Now you can see even more why using grit and gravel in moderation is so important, right?
The purpose of the organic potting compost is to improve water retention so the soil stays nice and moist for your juniper bonsai.
Lava rock is another water-retaining ingredient in bonsai soil. The chunks of rock also provide great soil aeration.
Pumice is a rock-based soil amendment that enhances water retention. It’s also a good medium for the roots to establish themselves, the same which cannot be said for lava rock.
Finally, there’s Akadama, a type of hard-baked clay from Japan that you’ll often see used as a soil amendment for bonsai tree species.
Sift Akadama before adding it to the soil mix.
Juniper Bonsai Indoor Lighting – What This Plant Needs
A happy juniper bonsai receives at least four or five hours of bright, direct sunlight per day.
That’s right, I said bright, direct sunlight.
This is a contrast to the lighting requirements of most indoor plant species, which is bright, indirect light.
Juniper bonsai species are not traditionally grown indoors, so they’re capable of handling more sunlight than your average indoor plant.
What do you do on those dark days of winter when the sun only comes through for an hour or two?
Or what about in the spring or summer where you have stretches of rain and the sun never appears?
Not to fear. You can always use an artificial grow light to provide the bright lighting requirements a healthy juniper bonsai needs.
Plants require light for photosynthesis, but they can’t tell sunlight apart from artificial light sources. To them, light is light and benefits them equally no matter its source.
Now, I mentioned that an indoor juniper bonsai tree needs bright sunlight (or artificial light) for only four or five hours per day. What about the other hours that the sun is up?
This plant appreciates periods of shade, especially when the sun gets strongest (which is in the afternoon).
If your juniper bonsai is getting too much shade, it will tell you, although it can take a while to notice.
The bonsai’s growth will slow down and can even stop if the conditions are that dark. Your plant can also grow leggy.
Legginess can be hard to distinguish between regular growth for some beginner indoor gardeners.
You can tell the two apart because leggy growth is long, barren of leaves, and usually stands out for its rather unnatural look.
What if you go too far in the other direction and leave your juniper bonsai out in direct sun for too long?
The plant can develop white spots across its needle-like foliage that look like they’re bleached.
Those spots turn brown and crispy, and the foliage can fall right off the tree!
What Temperature and Humidity Requirements Does the Juniper Bonsai Like?
The juniper bonsai has much a more generous temperature tolerance than your average indoor plant. Remember, this plant is traditionally grown outdoors, so that’s why.
Yes, that’s quite a range!
The hardy plant genus is frost-tolerant. Please don’t take that to mean that the juniper bonsai cannot be damaged by cold temperatures, as that isn’t true.
Once the temperatures approach single-digit territory, and especially if the temps are below freezing, nothing good will happen to a juniper bonsai.
Its cells could freeze and rupture, creating permanent damage that will force you to prune the dead spots.
Of course, since you’re growing your juniper bonsai tree indoors, I don’t think you’ll ever have to worry about the temps reaching 10 degrees, let alone single digits or negative temperatures.
Even still, it’s good to know what could happen to the juniper bonsai if it was ever exposed to temps that cold.
The heat tolerance of the juniper bonsai is generous, but if temps in your home or office reached 90 degrees, the tree could no longer handle it.
If the temperatures stayed over 100 degrees, the juniper bonsai could die.
Again, those conditions are very unlikely to occur indoors, but it’s still good info to know.
I want to talk for a moment about the humidity requirements of the juniper bonsai.
This tree genus needs humidity well over 50 percent. You’ll have to buy a humidifier for your juniper bonsai.
Juniper Bonsai Fertilizer – What Type and How Often to Apply
The growing season for juniper bonsai varieties begins in spring and lasts until autumn. On a three-week basis over the growing season, you should fertilize this tree to keep it healthy and strong.
You won’t use just one type of fertilizer for the juniper bonsai over its growing season, but two.
As spring gets underway and growth begins, use a nitrogen-heavy fertilizer.
At this point in the season, the extra boost of nitrogen will encourage the juniper bonsai to flower.
Then, as summertime rolls, switch to a fertilizer blend that contains a balanced mix of all three macronutrients, including phosphorus and potassium as well as nitrogen.
The inclusion of more potassium will maintain the bonsai’s health while the phosphorous will keep any flowers and fruits healthy, not to mention the root system as well.
The fertilizer you choose for an indoor bonsai tree should contain a rich variety of micronutrients as well, from copper to zinc, molybdenum, boron, manganese, and iron.
How to Train a Juniper Bonsai Tree
Juniper bonsai trees naturally develop their unique branch shapes, which some liken to a cascade.
That said, sometimes the bonsai branches can grow in undesirable shapes or at unwanted angles.
The best course of action at that point is to train the juniper bonsai to take on a more appealing shape.
A pruned bonsai tree is a lot easier to train. I’ll tell you everything you need to know about pruning this plant genus momentarily, so be sure to check that out.
Many indoor gardeners opt to use wires to train their juniper bonsai trees.
You can either single-wire or double-wire the branches. The most popular type of wire for these techniques is anodized aluminum, but you can use annealed copper as well.
If yours is a pine or conifer bonsai, then use annealed copper wire.
For deciduous juniper bonsai species, the anodized aluminum wire is the better option. It’s also more flexible.
To single-wire a juniper bonsai, you need wire that can encircle the tree’s trunk two times over.
Then take that wire and wrap it around the bonsai’s branch, beginning at the base and going to the tip. The wire should be wrapped at an approximate angle of 45 degrees.
To double-wire a juniper bonsai, pick two branches. The branches should be close to one another, but they don’t have to be adjacent. They should also be equally thick.
Take your wire and rotate it around the juniper bonsai tree’s trunk one to two times. Then wrap the wire around your first branch.
Like you would do when single-wiring, you should wrap the wire starting at the base of the branch and then work your way to the tip.
Then repeat that for the other branch, maintaining a 45-degree angle as you go along. This angle will help the tree develop thicker branches.
After single-wiring or double-wiring your juniper bonsai tree, you can gently adjust the wire-wrapped branches into your preferable shape.
Take the branch on the outside. Bend on the inside of the branch using your thumbs. If you try to bend the outside of the branch, it’s likelier to split.
You shouldn’t have to keep bending a branch into shape. Once the branch achieves the shape you want, leave it be.
Juniper Bonsai Pruning – How Often?
If you wish to prune your juniper bonsai, the best time to do it is as the active growing season gets underway.
You have two methods for pruning this bonsai genus, structural or maintenance pruning.
Structural pruning changes the bonsai’s architecture whereas maintenance pruning is all about cleanup.
Removing too many tips can weaken your bonsai, so you have to prune carefully whether you’re doing structural or maintenance pruning.
Look for bonsai tips that extend too far beyond the rest of the plant and interrupt the architectural balance of your indoor tree. Remove these tips selectively.
What tool do I recommend for the job? None other than bonsai shears or bonsai scissors.
These specialist tools will remove bonsai foliar tips cleanly, so please invest in a pair if you don’t already own one.
The goal when pruning the juniper bonsai is to allow lateral branches to develop. These branches will allow enough sunlight so the bonsai tree is healthy.
From the trunk, you’ll see some primary branches. Growing off the primary branch will be a series of secondary branches.
If the branches are very young, then they might not have hardened yet, but they will with time. Those branches are lignified.
Secondary branches that grow straight up or down are the ones you want to target first when pruning the juniper bonsai tree.
Don’t remove the branches entirely, but thin them.
Be sure to disinfect your bonsai shears or scissors using bleach or isopropyl alcohol when you’re finished.
Juniper Bonsai Pests and Diseases
To wrap up, I want to discuss the diseases and pests that can afflict the juniper bonsai. I’ll provide treatment options as appropriate.
Let’s start by talking about juniper bonsai diseases.
- Root rot: Root rot is a fungal disease that’s usually caused by overwatering. Compacted soil can entrap water around the roots as well. The roots die when they’re deprived of oxygen and have too much water. The foliage of the juniper bonsai will look sickly. Removing dead roots and reducing overwatering is the way to save your plant.
- Cedar apple rust: Affecting many juniper species, cedar apple rust can cause yellow foliar spots that develop spores. The spores can travel two miles to infect adjacent plants. Quarantine the affected plant, remove the yellowed leaves, and use a fungicide if necessary.
- Twig blight: Juniper bonsai tree species can develop either Kabatina twig blight from the Kabatina juniperi fungus or Cercospora twig blight from the Cercospora sequoiae fungus. The symptoms appear first in older needles, causing browning even though the tips are okay. Use a fungicide for treatment.
Many insects will try to make the juniper bonsai tree their home as well. Here’s an overview.
- Ants: The ants that invade juniper bonsai trees are not dangerous to humans, but they can damage your plant. They’ll pass along fungus and can sometimes deposit aphid eggs too. Applying food-grade diatomaceous earth where you spot ant nests ought to get rid of them.
- Caterpillars: Caterpillars may seem like harmless insects, but they can get inside the still-growing shoots of your juniper bonsai. They also eat the tips and weaken the plant. Use water and soap to rid the bonsai of caterpillars. Manual removal is another option if you don’t mind touching insects.
- Scale insects: The microscopic scale insects can invade the juniper bonsai tree in large numbers, creating a serious problem. Scale bugs will drink plant sap. To remove them, dilute rubbing alcohol with water and spray the foliage of your juniper bonsai.
- Vine weevils: The larval vine weevil can cause a plant collapse if these creepy-crawly bugs consume too much of the juniper bonsai tree. Diatomaceous earth is an effective treatment, as is manual removal if you can stomach it.
- Mealybugs: If your juniper bonsai is stressed or sick, mealybugs are a much likelier target. It might not be a bad time to transition the tree outdoors for a spell. You can also mix water and rubbing alcohol (70 percent) and apply it directly to the bugs with a cotton swab.
- Spider mites: Do you notice whiteish areas on the juniper bonsai? Is the tree showing yellow spots across its needle-like foliage? Then a spider mite infestation is likely. You can take care of these web-weaving insects by using water and rubbing alcohol.
- Aphids: Remember, ants and aphids are a two-part problem, so if you can eliminate one, you can usually eliminate the other. I’d recommend essential oils, neem oil, or even water and dish soap.