Answer: The first two plants are very hardy and low maintenance plants. Siberian Iris can be cut back (or the foliage pulled away) after frost has killed the tops or this may be done in spring. Autumn Joy sedum can be cut back to about three or four inches once the blooms fade, or they may be left until spring and then gently removed -- many gardeners find that this plant is good for "winter interest" so they leave it until spring. Lavender should not be cut back until late spring. This plant may winter kill unless it is planted in a spot with perfect drainage; even so it may die back a bit and the stems help to protect it some. In late spring you will be able to tell how much has been lost (trim out truly dead portions) and trim it back by about a third overall. The new growth will quickly conceal the pruning. All three will benefit from a few inches of organic mulch such as shredded bark placed over the root zone, but do not touch or cover the stems or crowns of the plants with the mulch.
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