Bonsai care (Caucasian spruce)

Placement

Caucasian spruce is not a houseplant, so it should spend most of the year outdoors. It loves light but also grows well in partial shade. Put it in a bright spot and, in summer, protect it from the scorching midday sun.  
From June through August you can keep it indoors in a well-lit place. From September, though, be sure to move it back outside.

Watering

A bonsai needs regular, careful watering.  
In nature, a tree's roots grow deep into the ground. If it happens not to rain for a while, the tree can still get the water and nutrients it needs through those deep roots.

Confined to a pot, a bonsai has no way to send its roots wherever they need to go. There is very little soil in a pot, so a bonsai depends on watering far more than a tree growing in nature.

It is also worth noting that on hot summer days the movement of water through the tree, and its evaporation from the leaves, regulates the plant’s temperature and protects it from overheating. As long as the soil is moist, the plant can keep developing normally even at very high temperatures. When water runs short, however, “scorch” spots appear on the leaves and shoots, and in the end this causes the tree to dry out and die.

How much and how often to water

How often a bonsai needs water depends on the conditions it is kept in, the soil in the pot and the species itself. A bonsai should be watered not on a strict schedule, but according to need. In late spring and summer, for example, watering once a day may not be enough. There is another common misconception: that watering while direct sunlight is falling on the plant is harmful to it. In summer it is sometimes actually essential to water a bonsai during the sunny part of the day. So don’t draw up a timetable along the lines of: “The bonsai must be watered once a day, in the evening.”

Some species need soil that is constantly moist, others need less moisture, but letting the soil dry out completely for a day or two very often kills the tree. Be sure to check the condition of the soil every day and water whenever it is needed.

There are a few simple signs that tell you the soil is drying out: as the soil begins to dry, its surface changes color; the surface of dry soil is noticeably harder. If your bonsai has been in its pot for several months, you can also tell whether it needs water by lifting it. The difference in weight is quite noticeable — dry soil is considerably lighter. Late watering is hard to spot on conifers. On a deciduous tree a delay of even a few hours can make the leaves droop, whereas on a conifer as much as a week may pass before you realize you have been underwatering it. The first sign is that the newly emerged needles weaken and droop.

Use ordinary tap water for watering. The drawback of tap water is its chlorine and high salt content. After regular watering with such water, the surface roots and the rim of the pot become covered with a white crust, which you will need to remove from time to time.

Make sure that after watering, water runs out of the drainage holes; otherwise only the surface may get wet while the soil deeper down stays dry. Quite often a bonsai is planted in its pot in such a way that much of the water you pour runs off the surface and out over the rim. In that case, pour slowly, only as much as the surface can hold without overflowing, wait for it to soak in, and add more — keep going until you are sure the soil in the pot is wet all the way through. Water flowing out of the drainage hole is the sign that the soil is thoroughly soaked.

Suppose the soil in the pot has dried out completely. If you look closely at the pot, you will see a gap has formed between the pot and the soil. If we water in this state, most of the water will run through the gap and straight out of the drainage hole.

In this case it is best to set the tree in a vessel larger than its pot, fill it with water up to the rim of the pot, and lift the tree out once the soil surface is wet. The excess water will drain out through the drainage holes. In spring and summer a tree needs much more water than in late autumn or winter. In winter you may find that you water the tree only once a month for the whole season (do not water a bonsai during frosts).

The time of day you water also matters. In late spring and summer, when temperatures are high, try to water so that the soil in the pot stays moist overnight. Water in the evening, after sunset. If you water only in the morning or at midday, the soil will soon dry out and the tree will spend practically the whole night in dry soil. In autumn, when the sun is no longer so fierce, you can water your bonsai at any time of day, though morning is best.

Now, about overwatering. When the soil around the roots is constantly wet, the amount of oxygen in the soil drops. This leads to the fine roots deteriorating. The damaged roots start to rot, and if the process is not stopped, a large part of the root system gradually rots away. As a result the tree first weakens and, if the situation is not corrected, dies. So once you have watered your bonsai thoroughly, let the soil dry out gradually, and only then water again.

Persistent rain can also make the soil in a pot too wet. But even a week of nonstop rain will not harm the tree. The danger is when the soil in the pot stays waterlogged constantly, for an entire season.

Bonsai care in winter

In winter trees are dormant, and their active growth is suspended until spring. The dormant period is just as essential to a tree’s vitality as the period of active growth. That is why bringing a bonsai into the warmth in winter simply because it “might get cold” is fatal to the tree. Of course, bringing it indoors for a day or two to decorate the room will do no harm. But if it spends the whole winter in the warmth, it will certainly die.

In temperate regions, where winters are not too harsh, a bonsai needs no special conditions to overwinter. But in regions where winter temperatures regularly fall low (-5°C and below), the tree must be protected from frost. This applies above all to the roots. A bonsai’s roots are not buried deep in the ground, so they can freeze easily. In Tbilisi’s climate the risk of freezing is lower. But if hard frosts go on for a long time, take a vessel much larger than the pot and bury the tree, pot and all, in sand or sawdust. In these conditions the roots are relatively well protected from frost.

Protecting bonsai in summer

At temperatures above 30°C, unless we take special measures to protect a bonsai, the tree can be damaged or even die. How well a tree withstands abnormally high heat depends on its own heat tolerance and on how many hours of the day the high temperature lasts.

The effect of heat is easy to see on a deciduous tree. A tree cools itself through its leaves, by evaporating water. At high temperatures it loses moisture quickly. When a bonsai gets too little water in the heat, the leaf temperature can reach a critical point. Wilting leaves are the first symptom of water shortage. In extreme heat a tree may go dormant prematurely (as it does in autumn). The leaves change color and drop — first the inner and lower leaves of the canopy, then the rest. When direct sunlight falls on a bonsai, the soil in the pot also heats up considerably. High temperatures can damage the roots too. Under these conditions the tree becomes less resistant to diseases and pests. On a conifer, however, these processes are hard to notice, because its needles don’t give such a “signal.” That is exactly why conifers need special attention in summer.

A tree can cope quite well with very high temperatures if you give it normal conditions to function. There are a few simple ways to protect a bonsai from extreme heat. Keep it out of direct midday sun, or rig up some kind of shade. Don’t stand a bonsai on a surface that gets very hot in the sun — stone, concrete, metal. Try to raise the humidity around the bonsai: mist it more often and water the area around it. Make sure the soil in the pot never dries out completely. Watering at midday is another way to cool the roots.

Fertilizer

For normal growth and development, besides the carbon (C), hydrogen (H) and oxygen (O) that a plant takes from air and water, a plant needs to obtain macro- and micronutrients from the soil. The macronutrients are nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg). Various micronutrients are also needed in very small amounts: iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), boron (B), manganese (Mn), sodium (Na) and other elements. All of these elements are vital to the plant’s existence, the macronutrients above all. An excess or deficiency of any one of them has a marked effect on the plant’s development. For example: nitrogen is needed to regulate growth, for the leaves and for fruiting. A nitrogen deficiency soon shows up as slowed growth. An excess prolongs the growth of new shoots. Nitrogen-rich fertilizer is not applied in the second half of the growing season. Phosphorus promotes the plant’s development and root growth, and strengthens its tolerance of drought and frost. Potassium gives the plant resistance to stress (very high or low temperatures, too much or too little moisture). An optimal amount of potassium improves the buds’ ability to overwinter and the plant’s resistance to fungal and bacterial diseases. Calcium is essential for normal metabolism in the plant. Because there is so little soil in a pot, the nutrients are used up quickly. That is why regularly applying a fertilizer that contains all these elements is as essential as watering. Without supplementary feeding a tree develops poorly, its leaves and needles lose color, and it falls prey to disease more easily.

For bonsai you can use either organic or mineral fertilizer, but you must not mix them together and apply them that way. There is fertilizer made specifically for bonsai that contains all the necessary elements. It can be either liquid or solid, in the form of granules. Liquid fertilizer is dissolved in water at a set dose, and the tree is watered with the resulting solution as usual. Plants absorb liquid fertilizer fairly quickly, so on conifers it is applied once every 3 weeks. Granular fertilizer acts over a longer period. It is either mixed into the soil or placed on top of the soil in special little baskets. With every watering a certain amount dissolves and gradually feeds the bonsai. You can order special bonsai fertilizer online.

If you can’t find such fertilizer, you can use a compound fertilizer sold in garden or flower shops. As a rule, these contain all the elements plants need. For bonsai it is best to use one that dissolves well in water; this kind is more convenient to use. The packet always states the composition in percentages (NPK) and how much water to dissolve it in. Be very careful when feeding and work out the correct dose, because too much can kill the tree. Ideally it should be NPK 10-10-10 and contain micronutrients.

Feeding usually begins in early spring, in March, and ends in autumn, at the end of September.

At Samto Kimia you can buy “Kristalon 20-20-20” fertilizer. Dissolve 1 teaspoon in 1.5 liters of water.

Misting

Misting is essential for both deciduous and coniferous trees. Start misting when the warm weather sets in, in spring, and continue until leaf fall begins. In summer it is best to mist daily — though of course there is no need to do so in rainy weather. Mist your bonsai when you water it.

Some water-soluble fertilizers are also meant for foliar spraying. This encourages lush, healthy leaves that are less prone to disease. There are also water-soluble liquid foliar feeds that give quite good results when sprayed. If necessary, mist with dissolved fertilizer or foliar feed once a week, or as often as you feed the soil.

Diseases and pests

Like all plants, bonsai get diseases and are attacked by pests. So it is best to spray preventively once a month from spring to autumn. Dissolve Ridomil Gold, Strobi Star and Actellic together in water at the recommended doses and spray. Never spray a bonsai in an enclosed space.