I am frequently asked about how the seasons can affect bonsai trees, so I put together this post for you. Please remember, that the advice is centered on the USA and may vary depending on your location around the world.
Spring is a good time for starting new bonsai tree projects and it is also the time for any pruning and training of last season’s bonsai trees. The plants then have a whole growing season to readjust to these changes.
Bonsai trees are usually very sensitive and thrive best in localities that offer cool nights, sunny days, and mist or rain almost daily.
Most of the United States does not have this climate, so special provisions must be made to compensate for this lack of ideal climatic conditions.
Extremes in light, rain, and wind are to be avoided.
Place your bonsai trees on a platform or table in your garden where the plants can receive 3 to 5 hours of direct sunlight a day. The site should be shaded, preferably in the afternoon.
If the area is subject to drying winds, put up screening around the plants to protect them. Screening also serves to provide the plants with shade.
Water the entire bonsai – both the plant and the soil – daily. If you skip even 1 day you can permanently damage the plant.
Make sure your plants are located where rain can fall on them, however plants should not remain wet or waterlogged for long periods of time.
During this period bonsai trees should be prepared in order to endure the approaching cold. Plant growth must be slowed down, so start to water plants less frequently to help slow growth, and reduce applications of fertilizers.
Do not use artificial night lighting (incandescent filament lamps) on plants after August 1st and do not prune or cut any branches after mid-August.
A major consideration in the winter months is the protection of bonsai from low temperatures and strong winds. Bonsai can only be left outdoors in climates where temperatures drop no lower than 28 F degrees. This is not the case throughout most of the United States, so a greenhouse, pit, or coldframe is necessary.
Winter frosts will seldom bother bonsai that are sheltered under the foliage of a spreading tree. Watch out for frosty periods, however.
It is easy to construct a simple coldframe for bonsai trees.
Before the ground is frozen, dig a hole at least 12 to18 inches deep in the soil. Make the hole as long and as wide as you need to for all your plants. Line the sides of this hole with exterior grade plywood, which extends 6 inches above the surface. Put 4 to 6 inches of gravel in the bottom of the hole, set your plant containers on this gravel, and spread straw around and over them.
Put a loose-fitting cover made of polyethylene sheeting or any similar material onto the frame and be sure the top of your coldframe is strong enough to withstand a heavy load of snow.
Ventilate on days when the air temperature is above 40 F degrees to keep the plants cool and dormant.
To purchase a coldframe kit, check your local nurseries or see catalogs of mail-order garden supply houses or check on amazon.com.
In the summer, during especially hot weather when the temperature is over 90 F degrees, water the bonsai plants once or twice a day. If the plants are in an unusually sandy soil that allows for easy drainage, they may require watering three or more times a day. Please be aware of this so as to avoid irreversible damage to your trees.
In early autumn, follow the watering directions for late spring. In late autumn, follow the watering directions for early spring.
In winter, keep the trees in a coldframe and ventilate the plants on one or more sides to keep them dormant.
Check for dryness every two weeks and only water the plants every second day, or less, as required. Just keep in mind that overwatering, rather than a lack of watering, kills many more bonsai trees.
To maintain optimal plant health and growth use fertilizer to supply nutrients.
Maintain the nutrient level in the soil mix throughout active growth with monthly applications of a diluted liquid fertilizer, but only apply fertilizer before and during active growth periods.
No special fertilizer is required for bonsai trees. You can simply use a typical liquid houseplant fertilizer (20-20-20 or its equivalent) diluted to one-quarter strength on the label.
The numbers 20-20-20 are the percentage, by weight, of the N-P-K (nitrogen, phosphorus, and potassium) contained in the fertilizer. These elements will enhance the growth of your bonsai tree.
What Does N-P-K Stand For & What Does It Do?
For the geeks out there!
N – Nitrogen is responsible for the size and amount of new growth and, to some extent, the green color of the leaves. Nitrogen is required for cell division and, also, protein manufacturing.
P – Phosphorus is necessary for cell division and is associated with good root growth and flowering.
K – Potassium activates cell enzymes and is directly related to overall healthy cell activity.
So there you have it, in a nutshell!