When the sun gets too hot…
There are various ways of helping our bonsai cope with sun and not literally cooking them on our benches in the summertime. They are in pots, but it doesn’t mean we want to fry a special root dish, in a soil sauce…
Because bonsai are in pots, they are very unlike trees in the ground. We want to reduce any similarities to a dog in a car on a hot day.
There are two situations… A cooler climate with rare spikes in temperature to 100 F / 38 C or higher that might last a few days, and then there are the hot summer areas that are always that high:
Sudden, rare spikes in cooler climates: Simply relocate your trees temporarily. Don’t bring them inside, but on the ground is a good start, under benches maybe, in light shade. Try to avoid full shade. Place them close together, but still retaining ease of watering. Plants near other plants cool one another with transpiration. Placing bonsai on grass is going to be a lot cooler than on a sidewalk.
Hot weather areas: These areas need site modification. Shadecloth over your growing area is a great option, reducing the ambient and radiant heat. Try 30% shadecloth for general use. Plant more vegetation around your benches, and reduce gravel or concrete areas. Put up fogger/misters that use very little water for cooling down during the heat of the day. Another, less attractive but very effective option is protecting individual pots with either towels or aluminum foil. Yet another is the same as cold weather protection, sinking your pots in bark or gravel. Gravel holds heat, though, so bark or something similar is better protection and is less likely to damage pots. Simply turning your trees so that the lowest branches shield the pot in the late afternoon can be significant. Be aware that entire site modification is much more effective than shielding individual pots.
In general terms (very general!), conifers will be more resistant to the effects of heat. Most conifer bonsai are happy up to 90 F. Most deciduous will do fine up to 80 F. If you’re consistently much higher than that, then you need site modification.
The advantages to any sort of heat reduction are:
- Moisture needs of the bonsai greatly decrease
- Foliage remains in better condition
- Less damage to roots
- Bonsai show less stress
Most importantly, do not ignore hot spells! Wing into action… They can seriously put your tree back, as badly as if they’d been hosting a very successful pest or disease.
Especially those who live in areas that are currently seeing water restrictions, reducing your water needs might be really significant if you’ve a lot of plants to take care of. Protecting bonsai from intense sun can make a huge difference to health and the ability of the tree to avoid other stresses. Trees can generally handle one stress, but multiple stresses get dicey. Bonsai already have one…they’re in a pot.