How to Crochet Clusters
Crochet cluster stitch is very similar to bobble stitch in that you will crochet a series of stitches, one after the other, leaving the last loop of each unfinished until the very end, when you will secure it all closed to create a single stitch. The difference is that bobble stitches are all worked into the same stitch whereas cluster stitches are worked into individual, usually subsequent stitches. Be sure to read the instructions carefully to see how and where the hook should be inserted for each "leg" of the cluster. The "legs" can be worked over adjacent stitches, or stitches can be skipped in between the "legs".
Here is how to work a 5-dc cluster stitch:
Double crochet into the stitch where you are going to start your cluster BUT leave the final loop on the hook. The steps to do this are: Yarn over, insert hook into stitch, yarn over and pull through (three loops on hook), yarn over and pull through 2 of the loops. Note that to complete the double crochet you would yarn over again and pull through the last two loops, but you are skipping that step here.
Repeat the sequence into each of the next four stitches.
Yarn over and pull through all five stitches.
In many of the other stitch variations, there is now the option to chain one to further secure the stitch closed. This is almost never used in cluster stitch but check your pattern instructions to be sure.
Once you work a cluster stitch, you may notice that it seems familiar. That's because clusters are used for decreasing. A 2 dc cluster is the exact same thing as a standard double crochet decrease, also called double crochet 2 together or dc2tog. A cluster may, therefore, sometimes be abbreviated as "cluster stitch" but may be abbreviated "dc5tog" (or however many stitches you are working together). Cluster stitches are used for the decreasing in Chevron Crochet.
Cluster made of 5 sc
Cluster made of 5 dtr
Double Woven Throw uses a 2 hdc cluster
Cluster Stitch Wrap is a great example of how a designer might have different names for the stitch than you're used to. This pattern uses dc2tog and dc3tog, which are clusters. It also has what is called a cluster, but all the stitches are worked in the same space so it's really a bobble!
Any combination of stitches may be joined into a cluster by leaving the last loop of each stitch on the hook until they are worked off together at the end. Working stitches together in this way can also be a method of decreasing.
Three Double Crochet Cluster
(Work over adjacent number of stitches specified in instruction.)
Work a double crochet into each of the next three stitches, holding the last loop of each double crochet on the hook.
Yarn over and pull the yarn through all four loops on the hook.