Answer: A few different things may be at play here. The problem may lie with a soil mix that is too acidic for healthy plant growth, due to the high amount of peat moss in the mix. If soil pH is too far off, nutrients get locked up in a form unavailable to plants. It's also important to avoid moisture extremes. If you're "soaking" the soil once per week, you may be creating a situation where plants really have an adequate moisture/drainage balance only a few days out of the week - the rest of the time may be too wet/dry for plants to grow well. Daily watering is better than weekly watering.
You'll find a great free bulletin on the Gardener's Supply Company website (www.gardeners.com) that gives a good rundown on the basics, and offers some recipies for soil mixes that work well for containers. Best of luck to you!
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