We have discussed in my previous blogs, the benefits of proper tree fertilization and how it aids trees in stressful conditions. What can also help is the addition of organic matter through soil injection. This process by itself or in conjunction with fertilization increases the retention of soil moisture, improving soil structure by adding and cementing soil particles. Other additives such as surfactants are available to aid in penetration and absorption and will remain in the soil for long periods of time. Surface application by physically adding mulch also aids in the retention, reduces soil evaporation and ads to increase soil moisture capacity. This needs to be replenished at times seasonally and I prefer native non processed mulch that decomposes quickly. Mulch should be 4-6″ thick keeping in mind to stay off the root flares.
For smaller trees there are irrigation vehicles such as bags with drip emitters which can irrigate small trees successfully for periods up to 3 weeks.
Finally, there is monitoring. Nothing can beat this. Use a soil probe and begin to work up a relationship with your soils.
Remember! For every diameter inch at breast height, a tree requires 10-15 gallons of water per watering.