There is lots of anecdotal evidence that seems to indicate that one feed brand is better than another. I for one don't believe there is much difference, if any, in growth rates, but look for a complete fertilizer, one with all 7 minor or trace elements. What is FAR MORE IMPORTANT is to feed correctly. Little and often, weakly, weekly are good watchwords. Note that a 20-20-20 feed compared to a 5-5-5 feed is 4x as concentrated, all other things being equal. This usually means it is 4x better value! I do find that most beginners are told to feed at low rates and this is a great way to start. I would recommend that you feed weakly, weekly for at least the first year of orchid growing. This will usually mean 1/4 tsp per gallon for most feed brands at every other watering, and every fourth watering in winter.
However, it has to be said that most commercial vendors and more proficient growers feed much more heavily than that. However, it also has to be said that these growers have state of the art facilities, with optimum temperature and light levels for each genera and loads of air movement and Reverse Osmosis (i.e. pure) water so they can feed at higher rates without burning the roots. The further away you are from this ideal environment, and the less experienced you are, the less you can push the plants with feed safely. There comes a point where the growth won't be any faster because you've burnt the roots and then the plant may die.
A great deal depends on the water quality. For example, in Seattle the water had a very low salt content (Total Dissolved Salts or TDS). Typically 40 parts per million (ppm) out the tap - this is lower than most bottled spring water! Back in the UK and further south in the US you may well find TDS levels of up to 500 ppm. Typically a maximum feed rate would be 1000 ppm alternating with plain water. What this all meant is that one could feed at 2x the feed rates of someone with poor water quality without burning the roots, i.e. you could add 960ppm of feed to this water to make a total TDS of 1000ppm, whereas a poor water quality grower may only be able to add 500ppm of feed. Half as much. Also, when you flush the pots every so often with pure water you'd get almost exactly that, pure water going through the pot. The poor water quality grower will have their tap water with lots of salts in it, so won't be able to achieve the same flushing effect with their 500ppm water. Water quality is very important but if you start feeding with a weak concentration of feed and flush well, you should be fine. Here in the UK now I feed relatively low amounts since my water quality is only around 500ppm TDS. Local utility companies usually give data on the web - look them up, it will give you an indication of what is possible, although the fine details are complicated and not discussed here. Several other orchid websites give more details of water quality issues.
I do also believe in using a couple of different feed formulations on a rotation basis just to make sure the plants get all the trace elements they require (and a balanced diet just in case). Current thinking is that bloom boosters (BB) do not actually increase flower size when applied to plants in spike - these BBs will increase the production of roots which might lead to better blooms later. I use BB to encourage roots in the spring, and to avoid the plants getting too lush and soft growth during the year. Note however that my opinion is that if you don't feed with enough nitrogen when plants are in spike, the spikes will be short. However, excessive nitrogen is known to wash out colours on Vandas. Many people claim that using high nitrogen feeds on Vandas will prevent them from spiking initially. I feel there is probably some truth in this, based on my experience.
Vitamin B1 additives do seem to encourage rooting and I do use them occasionally. Do not use too frequently, several people have reported these causing flower distortion if applied too often or in big doses and I have seen this on my plants when I've overdosed the water. The result was some flower crippling and strange features in the flowers. These were not present in subsequent flowerings.
Some people also report vast differences when switching from one feed brand to another, this probably means that they weren't feeding at the correct dose with their previous feeds, although some feeds may be somewhat more suited to certain potting mixes and water qualities and pH than others. For example it has been noted that with pure bark mixes and urea feeds, growth is poor but adding 20% peat to the mix corrects this problem. Alternatively use a feed with low urea (actually you want more nitrate and ammoniacal nitrogen) with pure bark potting mix.
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