It may sulk for quite awhile :-) Not all perennials need or should be divided. Iberis sempervirens is considered a subshrub, in that it is both evergreen and develops a permanent woody framework. Typically, perennial subshrubs do not get divided or do not respond well to division, in the manner of most other woody, shrubby species. That's not to say it can't be done, only that it is not recommended and the plant may be at risk if you do so. "Lavender cotton (Santolina chamaecyparissus) and several other perennials are actually small woody shrubs and should not be divided. These include perennial candytuft (Iberis sempervirens), lavender, rosemary, southernwood (Artemesia abrotanum), and several other artemesias. These plants often have rooted layers (branches that have developed roots while touching the soil). The layers can be cut off the parent plant, dug up and replanted as though they were divisions." I'd also add heaths and heathers to this list as well.

Oregano can be divided anytime, but preferably spring as new growth emerges or fall as you are preparing your beds for the winter. Take a sharp spade and first dig out one half of the clump, then cut the remaining clump in half again...or not. The idea is to remove the old growth. Chives are best divided in spring, also as new growth emerges. One way to thin them out and rejuvenate at the same time is after they bloom and before the flowers go to seed pull out the flower stems from the crown removing the entire stem and roots. Then dig the clumps you want to remove. If lavender is to be rejuvenated it is best done early spring just as new growth emerges. But you can start the process as soon as it finishes blooming by first trimming back the flowers, then prune only old or dead growth by pruning out no more than 1/4 of the plants current size, shaping it into a mound. I've read where you can prune it back again in November but I prefer to wait until early spring. You may want to verify the mature size of the variety you have because some lavenders, like grosso, are large plants. After you have divided the oregano and chives you can pot up your excess and sell or donate the plants to any organization that may take them.

Heuchera can be divided in spring or fall, unlike some fussier perennials. I haven't tried it in early summer, and I imagine that it would not be too happy but that it would recover, given *shade* and water for a week or so. You might consider planting it "as is" and dividing it in September, unless you're planning an event where you need things to be "finished" (as if gardens are ever finished!). My own preference is to always buy the smallest plants I can find, so I shop at nurseries where I know they'll have everything in 3 inch pots. I'll take a tray of small divisions or seedlings over a gallon pot any day - within 2 weeks the small plants will be well on their way to looking as good, and there will be a heck of a lot more of them for the same price. Some plants also get established much more quickly at smaller sizes - less problems with that mis-matched soil type barrier problem.

I have a number of candidates in mind. My inground gardening area is so restrictive and some of the plants have grown so well (and so big) that division is a must or I am faced with the potential smothering of smaller, more demure species by these bigger thugs. On the top of my list is the massive Baptisia I discussed earlier. Also a very happy (and huge) clump of apricot colored Kniphofia, a clump of lavender daylilies and Aster divaricatus (now Eurybia divaricata), which has grown far better and larger than I imagined in a pretty intensely full sun position. Never was quite that prolific in its more preferred part shade location in my old woodland garden!