I have quite a lot of trouble with whatever the bug is that drills holes in the leaf, and some of them fail to bulk up properly (which may be down to intermittent watering? They grow very fast, so are probably in need of a good supply of water. Perhaps I should put a drip irrigation supply in for the, this year?
I'm guessing you mean Leaf beetle?
Leaf beetles seem to adore all the oriental leaves- they made short work of my Komatsuna.
Intercrop with radish, Jamie- you'll distract the leaf beetles away from your orientals. It worked for me last year after the Komatsuna disaster. Leaf beetles LOVE radish and it doesnt really matter if your radish leaves get peppered with holes.
I sowed chinese cabbage Pe tsai in cell trays last year in June and July, and popped the strong ones into the soil as soon as they had a couple of true leaves.
The slugs were less interested in them than the lettuce and kale, but would still protect them.
They're a cool weather crop as everyone has mentioned, but you shouldnt have any probs with bolting if you sow them late (maybe pop them in after the spuds come out?)
You can also succession sow them- they do well under a bit of fleece well into November, going by mine last year. They actually hardied through the first frosts we got in Oct without any protection, but i may have been lucky!