Bonsai Gardening Secrets

Bonsai Tree Care

by Erik A. Olsen Copyright 2004

For Bonsai, every season brings a new type of care, as you will see from the following information. Keep in mind by maintaining up your bonsai tree care regimen regularly, your bonsai will continue (or start!) to flourish.


If you live in a region that experiences hard freezes during the winter, then some species of Bonsai will require extra protection from the elements. This would include Bougainvillea, Elephant’s Food, Ficus, Lantana, and Natal Plum and so on. The best option would be to move the Bonsai close to the house or under a deck or porch prior to the sun setting.

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Place each of them on a table, bench, blocks, or something else, as a way of elevating it. Next, take a piece of newspaper and cover the pots. To make sure the newspaper does not blow off, use clothespins or some other type of anchor. This way, you will eliminate damaging, vertical drafts. Keep in mind that you do not want to use plastic for the insulation.

If you have a garage, crawl space, or some other place that is not heated, that too would work. In this case, you would still place the newspaper on top of each pot. If your Bonsai does experience damage from frost, wait to trim it until you begin to see new frost.

Additionally, you want to reduce the amount of watering you give the Bonsai during the colder months. Typically, you would coordinate your watering with the current dew point so if you generally water your Bonsai once every two weeks in the winter but the dew point is exceptionally low for several days, then you might want to water more often, just during that time.

It is important for your Bonsai Tree Care that it not be fertilized in the winter. Instead, you want to wait until you see the beginning of buds.

Freeze Damage

When roots and stems freeze, there is both chemical and physical change. First, it is important to understand the three phases of freezing:

1. Water freezing in the Bonsai’s soil
2. Inter-cellular water freezing in the Bonsai’s tissue
3. Intra-cellular water freezing in the Bonsai’s tissue

Frozen Water in the Soil

Typically, this occurs when the water in the soil when the temperature of the three phases is the highest. In nature, water rarely freezes at a temperature of 32 degrees. However, in soil when ice forms, small particles are left that solute. In other words, the soil is not actually frozen, but the ice crystals in the soil.

While some people will tell you that freezing does tremendous damage to Bonsai, the truth is that the cells of the plant or tree are quite rigid and used to this type of pressure. Considering that the plants and trees generally used for Bonsai have been around for more than 1,000 years, it should provide you with some reassurance that your Bonsai will not die.

Now, if the roots are frozen for long periods and at extremely low temperatures, it is possible that some damage could occur. If you were worried about this, remember that plants to have built in mechanisms that keep them from freezing completely.

Freezing Inter-Cellular

Plants have another natural mechanism in which they expulse water from the cell protoplasm, which is located in the inter-cellular spaces. What happens is that changes in the cell membranes allow water to leave the cell, and instead, go into the spaces. Therefore, the water that does freeze is within the space and not the actual cell.

Freezing Intra-Cellular

Finally, when freezing occurs in the intra-cellular portion of the plant, the cells will die since they freeze. You would typically see few branches the following spring from this happening. The plants and trees however do have a built in mechanism referred to as, “Supercooling.” With this, the sap will stay at liquid temperature so it does not freeze.

Temperature Ranges

Each of the three stages has its own freezing point, as shown below:

1. 32 to 23 degrees F
2. 23 to 14 degrees F
3. -4 to -40 degrees F

Keep in mind that the root systems of plants do not necessarily go through the same level of hardening. For this reason, you will see that some trees have their roots underground where they are not subjected to rigid temperatures and other trees have their roots above ground.

When a tree is taken from the ground and then placed in a pot to be trained as a Bonsai, you need to remember that depending on the type of plant or tree, you could be subjecting the root system to temperatures and an environment that it has never experienced. When this happens, the tree could die.

For this reason, it is crucial for proper bonsai tree care that it be protected during the in wintertime, especially in the first few years of change. The best way to provide protection is to place the Bonsai in the ground outdoors during the winter so that it is in its natural protected state, or if you do put it in a pot, add mulch. As long as the roots are not exposed to killing temperatures, it should thrive. However, if the plant or tree does die, do not be overly surprised.

Tissue Dehydration

Another problem relating to frozen soil is that while typically this is not a problem for the Bonsai, there are exceptions. First, if the temperature of the above ground tissues should rise dramatically where the soil water stays frozen, then transpiration of the water might occur from the shoots.

As the Bonsai grower, you can help avoid the problem by creating some type of windbreak for the tree. Excellent options include using a greenhouse or coldframe. Even if you have an area in the garage or on a porch or deck, that too would work. If the Bonsai is outdoors, again, make sure it has plenty of mulch built up around the base.


To keep this all straight, you can refer to this guide any time you need.

If the Bonsai will be created from a temperate plant, it will go dormant in the fall. At that time, shorter days and falling temperatures will be a consideration. When exposed to shorter days and lower temperatures, any frost will encourage the plant to begin cold hardening, as a way of sustaining itself through the cold months.

Bonsai from temperate plants will need to have a time of “chilling”. This will help break the dormant time, thus starting re-growth. Typically, this time is considered anywhere from250 to 1,000 hours with temperatures ranging from 34 to 50 degrees F.

Any buds, leaves, or shoots above ground from temperate plants that have gone through the cold hardening phase can generally handle very low temperatures.

The Bonsai roots from most temperate plants will not cold harden, which you would find in above ground plants. Therefore, they are very susceptible to low temperatures, becoming damaged quite easily.

Freezing soil it not always a threat to your Bonsai. However, if the Bonsai has frozen soil and then exposed to long periods of shoots being in the cold or drying winds, you could have damage or dying shoots.

Always allow your Bonsai to go into its dormant state and cold harden properly. For instance, exposure to the first fall frosts is important.

Keep your Bonsai in an enclosure or pot that is well watered and where temperatures can be controlled all winter long.

Any plants that are removed from the protected area during cold temperatures could cause the plant/tree to die


Spring is a busy time for Bonsai in that you will be working with re-growth, new growth, potting, and styling. In addition to this, you may have some potted Bonsai that have been in their pot for two years, meaning these too need to be pruned, shaped, and repotted.

However, to change the appearance of your Bonsai, this is the time to consider something different, which could be done by repositioning the tree in its current pot. If you prefer, you can completely change the style, whichever you prefer. When you begin to see new leaf buds, you want to pot or repot the Bonsai to ensure they have adequate internal reserves to keep growing while the feeder roots are absorbing nutrients. However, if you do not provide the Bonsai with root pruning, then these feeder roots will become active quicker.

When working on your Bonsai during the spring, you should find a shady place out of the wind, and preferably with a 30-degree dew point. To ensure the root balls stays moist, you also want to keep a spray bottle on hand. During the spring, you will be cutting various parts of the tree so you want to make sure you produce clean cuts by having sharp tools.

If the plant is young, then it will require more pruning of the roots. To accomplish this, the tap should be removed along with the larger roots, using concave cutters. Take care not to cut anything except the roots. Spring is the time of the year when you will fertilize the Bonsai, using components of Nitrogen/Phosphorus/Potassium. The Nitrogen will benefit the leaves and stems, the Phosphorus the roots, and the potassium, the flowers.

While you could use non-organic fertilizer, your Bonsai will actually do much better with organic matter. For your repotting soil, the tree would do well with a little application of slow-release, solid fertilizer that contains micronutrients. Now is the time to examine the growth of the roots. If they have not grown as much as you would like, then change the soil to one that is coarser and that drains better.

Additionally, reduce the amount of nitrogen, while increasing the level of phosphate. Finally, the roots should be left alone for a minimum of two years. Make sure the tree is out of direct sun and wind, for at least one week. Then very slowly, you will introduce it to these elements so it can adjust naturally.

Although you will still water on a regular basis, initially reduce the amount you give the tree. This transitional time will help your Bonsai look better. Then after two to three weeks, you will add organic fertilizer. If you have a Pine or Juniper, you would also want to add fish emulsion once a week. Then any flowers should be cut off at the end of their blooming period so the Bonsai will look stunning the next year.

In most cases, you would not want the trunk or branches to become too bulky. To make sure this does not happen, any new side buds and branches should be maintained at a shorter length. The best guideline is that active buds should be limited to pairs, keeping no more than two buds per branch. Going back to Pines and Junipers, these may require weekly trims to help ramifying growth.


Summertime always presents unique challenges for Bonsai but with the proper information and tools, you can maintain your plant’s health.

As an example, the following tips will help your Bonsai not just survive but thrive during the summer months:

Make sure you are using fresh, healthy soil

Every week, rotate your Bonsai about one-quarter turn so that the entire plant receives an equal amount of sun and fresh air

Keep the Bonsai well trimmed, specifically species that tend to get out of control such as elms and junipers

Pay attention to the water levels along with the retention for the type of soil you are using

After noon, make sure your Bonsai has an overhead shade cloth

Place your Bonsai on slatted workbenches on the lawn or gravel and then in the morning, soak the ground. Then, occasionally, provide the Bonsai a good misting.

While setting your Bonsai near a pond or swimming pool is fine, be very careful about placing them in pans of water in that the sun can reflect and cause problems

Set your Bonsai in groupings but make sure none of them are touching

Protect your Bonsai from the western or hot afternoon sun

Grow your Bonsai in a growing bed as opposed to pots

For maples and other thin-edged leaf bearing Bonsai, water them with reverse osmosis or distilled water

Fertilize the Bonsai regularly using half the normal strength

If you notice any wilted leaves, reduce the amount of water and place the Bonsai in the sun

Remember that only your larger Bonsai should be placed in full sun. For instance, plants such as elephant food, bougainvillea, Texas ebony, junipers, and dwarf myrtle would do fine in full sun but any Bonsai that are root-pruned or ones you have recently repotted.

During the late summer and early fall months, be sure you use fertilizer that is high in phosphate. A great blend would be 10-60-10, which helps the buds build a reserve for the following spring.


For the fall, you need to be careful with your Bonsai, not allowing them to get out of control. Many times, species such as elms, junipers, and pomegranates grow very fast in the fall so you will need to keep new growth pinched back.

One of the most important things to remember during the fall is that you need to monitor your water retention for the soil mix very carefully. If you are not cautious with this, you will easily over water, killing or severely damaging the plant.

Giving your Bonsai a fertilizer high in phosphate, using a blend of 10-60-10 is beneficial. What happens is that this type of blend will help the buds maintain a reserve so that in the spring, they can flourish. Additionally, for your juniper and pine Bonsai, you probably want to wire them during the fall, constantly checking them for fast growth that could cause scarring.


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