Last year my container plants started to go downhill about the end of July. How can I keep them attractive until the end of summer?
Your experience is very common. We give our containers fertilizer when we plant them and are very attentive in watering to get them started. As the weather warms in July and we are busy with other summer activities, we sometimes forget to water container plants.
By this time most of the fertilizer is either used up or washed out of the soil in containers. Even if you used slow-release fertilizer it is probably mostly gone by now. Slow-release coated fertilizer such as Osmocote is the best to use now. One application will probably last for the rest of the summer.
One of the earliest signs that tell us plants need fertilizer is lower or older leaves start to turn yellow and then fall off. When plants are short of nitrogen they transfer it from old growth to new growth. Supplying fertilizer keeps the older foliage active longer.