Answer: I think your peppers are way too crowded. You might allow about a foot of space in beteen each plant in the garden! Maybe you could squeeze three in a row in your 18 inch box if you are careful to feed and water them regularly all summer. They will need space to grow and mature, the roots need room to spread and they also need good air circulation to stay healthy. Maybe you could share the extras with some friends, you can transplant them easily.
Peppers, like tomatoes, usually start to grow well when nights are reliably above about 50 degrees. They should be in full sun all day long or for a minimum of six hours a day preferably including the hour of noon.
I hope you used a good quality soilless potting mix formulated for container plants. Your box should have drainage holes in the bottom to allow excess moisture to escape.
You need to water so that the soil stays evenly damp or moist but not sopping wet. To know if you need to water you can dig into the soil with your finger and see. If it is still damp do not water yet. When you do water, water thoroughly and make sure it soaks in to moisten all of the soil.
You will also need to fertilize your plants. Use a water soluble fertilizer with an analysis of 10-10-10 plus minors or similar proportions. Read and follow the label instructions.
Good luck with your peppers!
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