Yes you will need to clip the old dead leaves if you want to keep them tidy. Also lookout for 'reverted' leaves on some of the unstable cv. these are easily removed by pulling the entire leaf fan from the clump.

If they are happy you will need to divide them every 3 years or so (unless they stay dwarf)to keep them from becoming too large. They don't particularly enjoy being dug up so I just split them with a shovel or axe and remove a portion from the ground (which can be planted elsewhere).

Chad

Thanks Chad. Good advice. I am surprised that I got any advice at all since I didn't spell phormium correctly in the title and asked about an australian native in a new zealand native forum.

Actually it is a South African forum... You don't say where in southern California you are, but many of the more colorful foliage forms of Phormiums will sunburn in full sun if not near the coast, and they get exposed to 85/95F degree weather at mid-day. The forms with recurved foliage as opposed to upright are the most prone to sun burning, especially the yellow leafed forms. They usually do better in hot areas if they only get morning sun or dappled shade. I don't know why your contractor would have gone to all the trouble of french drains for these, as they are not that sensitive, but they do appreciate a moisture retentive yet well drained soil. They aren't sensitive to fertilizers in the same way as Protea family members.

If you are getting lots of dried out leaves and burnt tips, rather than sunburnt foliage, it is more likely a problem of too much or not enough water. If the watering regimen is correct, they shouldn't be showing signs of dead leaves and dead leaf tips on such relatively young plants, and should have settled in after 6 months of being planted out.

You'd probably have a better idea of what is wrong with how yours are being grown if you look around your neighborhood for Phormiums which are doing well of the same cultivars. I've seen them have problems with mealybug at the base of the leaves/root crown if they don't get good air circulation or are planted too deep or leaf bases are covered by mulch, and/or they can dry out too fast if the root crowns become exposed because they may have been planted too high.

They should be thriving if you are near the coast, and they get the right amount of watering, as these are nearly indestructible plants in the right spot. You will need to keep an eye on plants which have the foliage revert to more boring green, as these parts of the plants will overtake the more colorful foliage.