There are many suitable formulas suitable for orchids. Orchid Focus Grow and Orchid Focus Bloom are recommended for those with a small collection, the DynaGrow range is suitable for larger collections as it is highly concentrated. These and more available from the Retailers listed on the links page.
Alternatively you might like to "mix your owm" using the formula suggested by Mike Armstrong of Mikandra Orchids:
Many years ago, I became frustrated with the lack of information on what to feed orchids. After finding the information I wanted, which came from tests on orchids over a long period, I adopted the following regime. In the tests, it was found that orchids need very little Phosphate (Phosphate is the middle element in the N P K on a packet of feed)! Excess Phosphate locks off the nutrients to the plant in the compost and accelerates compost break down. It must be stressed at this stage that the use of conductivity meter is essential. The regime run on a monthly cycle is as follows:
All the above feeds can be obtained from Chempak's mail order division Garden Direct, (some also from Garden Direct Online) Dept MO, Hillgrove Business Park, Nazeing Rd Nazeing Essex EN9 2BB Tel: 01992 890550 or as individually packed chemicals at most garden centres (see details below). The strengths of the feed controlled by a conductivity meter are as follows:
The whole idea of the above regime is a little and often. The
above strengths are only a guide and can be altered to suite each
growers needs, and have only been used with rain and reverse osmosis
water, not tap water!
Mike Armstrong, Mikandra Orchids
N.B. For the benefit of those not at the meeting when Mike talked about this regime, here are a few notes to expand on the theme. We have found all the individual chemicals mentioned, in dry form, at our local (English) garden centre. J Arthur Bowers Sulphate of Ammonia (Nitrogen), Sulphate of Potash and Super Phosphate in 1kg size, also Chempak Calcium Nitrate and Epsom Salts (Magnesium Sulphate) both in 750g size. As the Calcium Nitrate is in fairly large granules we found it useful to grind them to a smaller size in a pestle and mortar to facilitate a more even mix.
The no-phosphate mix is dead simple i.e. using a 15ml tablespoon, mix one tablespoon of Nitrogen with three tablespoons of Potash to give a total of 60ml then add one tablespoon of Epsom Salts and one tablespoon of Calcium Nitrate (six times 2.5ml rather handily equalling 15ml!). Then comes the tricky bit, disolving it in water. We found that in the rainwater we have collected 1-eighth of a teaspoon/0.6ml of the mixture dissolved in 2 gallons/9ltr of water gave a reading of 400 microsiemens, the maximum recommended for March/April. We actually mixed it in one litre of water at first and kept adding water and re-measuring until we reached 400 microsiemens, which happened to be with 9 litres of water.
Mike did say that this could be used as a foliar feed, so that is what I
intend to do with plants grown in sphagnum moss. I have no idea yet
whether this regime will be any better or worse than any other, only time