Growth habit is all over the board. Literally.
Phals., for example, simply add leaf after leaf. They add to the tops side and occasionally lose on at the bottom. A lot of people tend to get worried when they see the lowest leaf on a Phal dead or dying. That is NOT a problem. All living material has a finite lifespan, including orchid leaves. They simply can’t live forever. Imagine a rose bush or any other plant that simply never shed its leaves. Even those with the LONGEST lasting leaves turn them over with some sort of appropriate timeframe. The lowest leaf on this Phal. died. I could cut them off when they are pretty well gone, but it’s not necessary until you find the dead leaf is attracting pests. As long as they are clean, I prefer to leave them in place until they literally come off in my hand as the one in this picture. As long as it’s the lowest leaf that is dying, and new healthy leaves are growing on top, and especially if the plant is throwing off new, fat healthy roots at the juncture of the lowest leaves, then everything is fine! Because of this growth habit, there is never anything to trim other than excessive roots when you repot. And you simply repot it a little lower each time to include some of those new lowest roots in the bark and to compensate for the loss of the lower leaf or two.
Cymbidiums, Oncidiums, and the like, grow from bulbs that form at the surface of the bark. These plants generally grow by sprouting new bulbs. Eventually the pot will become very crowded. So when this type of plant is repotted, you simply separate the bulbs into smaller groups and start new plants from the divisions. In this picture of a Cymbidium is a natural bundle of leaves at the surface level, and the beginning of a shoot that will become anew cluster. New clusters will continue to sprout from the surface of a healthy plant, and eventually crowd the pot to the point of needing to be separated into smaller clusters.
In this picture of of Oncidium Sharry Baby, there are actually distinct swollen bulbs at the surface of the bark. The bulb will grow and swell, leaves will grow out of the top of the bulb, and flower spikes will come out of the joint where the leaves join the bulb. Over time, leaves will die and leave a swollen bulb all alone. These bulbs are reservoirs for holding water for the plant, so as long as the bulbs are green and viable, I simply leave them in place. Occasionally one will dry and shrivel up completely, in which case I simply trim it away when I separate the plant into different clumps of bulbs and create new potted plants to give away.
Occasionally, you’ll find an orchid that sprouts new growth high up on a stem. These can appear to be miniature versions of the main plant, including roots that simply hang down in the air. Dendrobiums tend to do this frequently.
The bulb-type orchids ( called pseudobulbs for reasons I don’t understand – they are BULBS to me!) such as Oncidiums and the like, will have pseudobulbs lose their leaves as they age, with the bulb potentially staying viable for long periods of time (at times years), and then die. If you see a dead pseudobulb occasionally on an otherwise healthy plant, this is absolutely nothing to worry about. I don’t even both attempting to remove them until I repot, at which time they are simply trimmed away. I might repot sooner if I have a few, because they have a tendency to get “mushy” and its decomposing might attract pests or disease. I’ve never had a problem with them, and I don’t want to express any paranoia here.
I simply trim them away when the opportunity arrises, generally during repotting. Here is a picture of a dead pseudobulb on an otherwise VERY healthy Mtssa. C. M. Fitch ‘Izumi” and a picture of its extraordinary flower. These are very easy-keeping orchids. They thrive in my normal household temperature range, fit well in my twice-weekly watering regimen and appear to love the Hawaiian Bud & Bloom that I feed them regularly. (See “Resources.” I dilute to 1 TSP per gallon of water and pour the weak solution over bark after watering – from February 1 to November 30 each year.)