Summer Care

By Marty Mann

Editor’s Note: This article appeared in our July 2005 newsletter, quoted from the GSBF-Bonsai website about that time. The original title was -
A Simmering Summer - Time for Special Care

The months of July and August, bring a period of slow growth and relative inactive changes in bonsai. However, it should be remembered that the trunk and branches continue to swell and develop. Watch the wires applied in spring in order to prevent unsightly and destructive cuts. 

It’s also time to be attentive to the watering and feeding requirements of the trees to maintain good health during this stressful period. Watering should not be neglected. Foliar spraying is best done early in the morning or in late afternoon. A fresh spray each morning removes impurities that have settled during the night. Excess moisture in the crotch of leaf clusters or on their undersides creates environments ideal for the formation of fungus and related health threatening damage. 

Potted trees build up considerable heat and a lack of moisture allows fine roots to dry. During this period it’s a good practice to water less but more often to replace the expiration of moisture by drying winds on leaf surfaces. Resist the tendency to over water when you see the signs of distress in the form of wilt or needle drop. Test the soil regularly to be sure it is actually drying out before you arbitrarily soak it again. For balanced plant health, moisture must be consistently renewed. Daytime water adhering to leaves can literally cook them and cause severe leaf burn. If overhead watering is unavoidable, do so early in the morning to give time for surface evaporation. 

Summer vacationing puts an additional burden on your 'bonsai sitters. Try forming a mutual watering pact with fellow bonsaiists. You do for them when you can and they will do for you. It’s a great working arrangement and considerably safer than trusting your “babies” to strangers.

A suggestion would be to let them water your trees for you for a few days before you leave to be sure they are following your instructions. Trees requiring special care should be grouped together to simplify attention. Don’t trust your automatic watering system without the backup of someone who can check from time to time to audit its functions. 

Azaleas require special care and attention in July. They have just experienced a flush period of spring renewal, spurts of new growth and an extended period of colorful, showy blooms. After the flowers begin to fade and lose vigor the current year’s crop of new shoots may be cut short. General constructive trimming may be done at this time. Remove all shoots that have grown upward or downward.

Cut back to only two shoots on each branch. Trim back to at least two or four leaf sets on each shoot to allow new buds to form and new branch divisions to occur. Don’t cut back to bare wood at this time of year. Azaleas generally bud back on bare branches in spring; however, summer cutting in this manner risks branch die back. Branches may be carefully wired to establish form and style. If trimming azaleas is done after July, you risk losing the plant’s ability to form new flower buds for a show of color next spring. 

A regular feeding program is important. A change of your usual food is timely during the summer months when the general growth is slower but the need for nutrients continues. Feed with a product that has less nitrogen but more potassium and phosphorus to harden the woody parts and induce the development of the fruit and flower buds formed during the past few months. If your plants appear to be stressed due to the heat, then reduce your feeding formula to half strength. Particular care must be given to pomegranates, olives and other the warm climate tropical material that continues to grow during this period. 

Watch your sunshine exposure. Move leafy deciduous trees out of full sun and into shaded or partially shaded areas to protect the leaf surfaces and fine rootage. Rotate all material on a regular basis for even light exposure. Keep the humidity high and the air moving around the trees. Check the general shape of everything. Pinch excessive new growth to balance the trees and allow more light to penetrate the interior. Remove extraordinary large leaves that tend to appear on healthy trees from time to time. Continuous pinching encourages 'bushiness and twiggyness'. Keeping the trees out of the hot sun tends to improve the maturing fall colors.

Summer is the time to monitor the shari and jin portions of the styled trees. Apply a second application of lime sulphur (i.e., Orthorix Dormant Spray) to the dampened dead wood areas to protect against wood rot. Avoid seepage of this chemical into the soil and root area. Avoid live wood surfaces. 

Leaf pruning begins in late June or early July. Healthy deciduous trees that have recently been well fed may by defoliated now. This timing gives trees an opportunity to recover and begin the formation of a secondary set of leaves. Most deciduous varieties benefit from this activity if it is not done too often. Biannually is best. Be sure to protect the new growth by keeping trees in a cool shaded area until they have hardened and regained size and strength. Continue regular pinching of new growing tips to prevent excessively long internodes.

With the beginning of summer, most transplanting must be curtailed. Some material such as pomegranates, tropical trees including ficus, cotoneaster, bamboo, palms, wisteria, olives, and pyracantha can be re-potted during the warmer months; however, don’t allow the fine feeding roots to be exposed to drying air. A good technique is to mist the roots and dust them with a fine soil mix as a coating. This protects them during the repotting process. Warm sunny weather stimulates root growth and helps to re-establish the tree. 

July and August is the time to appreciate the fullness of bonsai in their most mature condition. Don’t treat them as frail or tender plants. Keep them rotated and cared for at all times but don’t neglect or overindulge.