Answer: It doesn't sound as though you were very successful with your first garden, and that's a shame considering how much work you put into it. All soil can benefit from the addition of organic matter, so tilling in peat, manure and additional top soil should make your garden bed brimming with moisture-retaining, nutrient-bearing material that is loose and perfect for the plants you placed in the garden. If your plants did not thrive, it might be because they all grow best in full sunshine (part shade for the astilbe if your summers are hot), or it might be because they didn't receive the water they require throughout the growing season. If frost nipped the tops of the plants back, the roots will survive the winter and produce new foliage in the spring. If the plants died before your first frost, they probably won't come back next year. Based upon the above, you should probably leave things alone to see what sprouts next spring. If nothing shows up, dig the bed up, remove the dead roots and try again. Be sure to water your new plants well, supplying one-inch of water per week to the bed (more if the weather is hot and the plants seem to be wilting). A 2-3 inch layer of mulch around the plants will help retain moisture and suppress weeds, so unless you piled the mulch over the plants, or it's so thick that water can't penetrate, I don't think excess mulch material caused the death of your plants. Follow the above guidelines and you're sure to have healthy, attractive plants next year.
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