July and August are usually the two most stressful months for bonsai in our neck of the woods but this year has been different, so far. Keep an eye on the weather forecasts and be ready to change your habits. Going into July and August and usually later you will need to keep your bonsai as cool as possible. That means no sun on the pot and soil where the roots are. Without going into a lot of detail some considerations you will be looking at are:
- Shade cloth.40% for pines, junipers, tridents. 50% for less tough plants. 60% on the west side.
- Water schedule. At 2pm to cool the soil, at sundown to cool soil and refresh overnight, morning as necessary. This is optimum. You must adjust that schedule and soil mix to work with your schedule.
- Soil covering. Chopped long fiber sphagnum to retain moisture also helps keep soil cooler.
- Protect from late afternoon sun. Low humidity lets the full force of the heat come through.
- Consider foliage misting especially on junipers. Many species in the wild open stoma at night to take in dew. Some broadleaf plants do foliage feeding, usually for localized needs in the area of the leaf.
- Keep insects under control especially the sucking ones-mites and scale.
- Pot protection. Shade sides of pot. Use old cloth, shop towels, make boxes to fit. Some air circulation around the pot should be allowed.
We usually do not fertilize our bonsai enough. However during these hot days you need to exercise care. Slow release organics are best. Chemical fertilizers may burn roots if the soil temperature (remember the sun factor) gets too warm, probably like upper 90s or more, be sure to read the label for guidance. Most recommendations are to feed the trees with organic fertilizer balls. Many are available commercially or you can make your own, depends on how many bonsai you have. Even with the fertilizer balls I like to give a feeding with a liquid fertilizer every other week also.
Also watch for signs of insect problems. The spider mite will always be near. Others to look for are scale of various forms, aphids, bagworms, and mealy bugs. Preventative medicine is best, spray on a regular schedule. By the time you see signs of bugs, the damage is already done, especially from spider mites. I use the organic foliar feed (1 Tablespoon each of fish emulsion, liquid kelp, molasses and 5% apple cider vinegar per gallon water) applied weekly to control all these. You can use some of the other organic controls or a chemical according to label directions. Read the label directions carefully. Do not apply oil based chemicals to buttonwoods. A hose end sprayer does not work very well, its droplets are too large and you have little control over where it goes. Use a pump sprayer with a fine spray and cover both top and bottom of leaves, trunks and all twigs. Most controls, whether chemical or organic, must be done on a regular schedule for good control. If you wait until you see damage it is usually too late.
When checking the results on your plants after spraying remember that the spray usually will not remove the 'evidence' of problems. The webs will still be there after the mites are killed, the shells of the scale will be attached to the leaf or stem. These will have to be removed by hand, by a jet of water, or some other way. A soft toothbrush works well on the scale shells. There is no damage from this leftover evidence but it prevents you from seeing any new infestation that may occur.
Be careful when pruning the spring flowering species. They will set buds for next year's flowers in the fall. The Kurume azaleas set their buds in July and the Satsuki a little later in August. You need to find out if your particular flowering tree blooms on new or old wood and when it sets buds so you can keep it in shape and yet will not prune next year's flowers off.
Tropicals, buttonwoods, fukien tea, serissa, fig, etc., should be repotted during the summer while they are growing strong.
When the humidity is low, I mist my junipers in the evening. I believe the story that in the wild junipers open their stomata in the cool of the evening absorbing any dew that may occur and close in the heat of the day to conserve moisture. The other species may get a foliage spray in the morning.
The humidity in summer varies quite a bit but when it sticks around for a few days look for fungal problems to appear, mildew being the most prevalent. Black spot will show up if the foliage stays wet very long. Foliage watering in the morning will usually not be a problem because it dries pretty quickly. Treat with potassium carbonate which you can find at any nursery with a decent organic section. There are several chemical sprays available too.
If you use the Boon technique for growing pines, now is the time for removing the candles, earlier on bigger trees later on smaller ones.
By John Miller - Reprinted From 2015