So, you're starting to get serious about orchids. You've figured out the basics of light, heat, watering, humidity, and repotting. But with all of the orchid fertilizers and amendments out there, how do you keep it all straight?
In my beginner days, I messed around with all kinds of fertilizers. They were often found on sale, promised as an "all-in-one" fix, or otherwise from big-box stores and simply labeled "orchid fertilizer." I knew about NPK ratios from my Master Gardener training and reading orchid guides, but I didn't know what was current best practice for orchids. One winter, after noticing that some of the oldest and most reliable orchids in my collection had mottled and yellowing leaves, I researched the symptoms and found out that it was due to Calcium and Magnesium deficiency. I ran through all of my assorted fertilizers, only to find out that indeed NONE of them had these essential micronutrients. So I read further. Through the assistance of many books and American Orchid Society articles about orchid fertilizers (Sue Bottom has several wonderful essays on the subject), I began to make smarter choices for my orchids.
The first step was to drop all fertilizers that didn't contain micronutrients. For my water quality, MSU Orchid Fertilizer (RO/Rain/Tap) was the best choice. (If you haven't checked the pH and TDS of the water you use for your orchids--and adjusted your fertilizer to suit--you probably should. Otherwise, look for knowledgable orchid growers' publications on the subject. Googling "orchid water quality" is a good start.)
Many orchid books and websites advise that we fertilize our orchids "weekly, weakly." I find that MSU is better used for most orchid species by following the directions on the package: 1 tsp/gallon during active growth, 3/4 tsp in rest season. Its 13-3-15-8-2 formula is safe to use at the recommended strength, especially when balanced with regular flushes of pure water.
After years of experimentation, I've come down to using only the fertilizers and amendments listed below. To wit, Quantum Orchid and MaxSea have both shown beneficial effects across many orchid genera. I do utilize a bit of extra CalMag in periods of rapid growth, because I noticed my largest and fastest-growing phalaenopsis orchids this year needed a bit more than MSU was able to provide. SuperThrive's efficacy is widely debated, but many orchidists still utilize it on faith. (If this is you, keep using it! It's just not proven its mettle for me.) I use Mosquito Bits to make sure fungus gnats stay at bay. (Several places online say that fungus gnats do not harm orchid roots, but I am aggressive about fungus gnat larvae control.)
What follows is my general guide for orchid fertilization and amendments. The picture below was my first attempt to map it out; lower down I list a month-by-month guide.
Orchid Fertilizer/Amendment Schedule
These guidelines assume that you water once per week. First, water your orchids with pure water, then fertilize them. Every fourth watering, do not fertilize.
MSU= MSU fertilizer; MB = MosquitoBits;
QO = QuantumOrchid; CM = CalMag; MaxSea=MaxSea
January
Week 1: MSU 3/4 t/gal, refresh MB
Week 2: MSU 3/4 t/gal
Week 3: MSU 3/4 t/gal, QO
Week 4: flush pots with water only
February
Week 1: MSU 3/4 t/gal, refresh MB
Week 2: MSU 3/4 t/gal
Week 3: MSU 3/4 t/gal, QO
Week 4: flush pots with water only
March
Week 1: MSU 1 t/gal, refresh MB
Week 2: MaxSea 2 t/gal
Week 3: MSU 1 t/gal, QO
Week 4: flush pots with water only
April
Week 1: MSU 1 t/gal, refresh MB
Week 2: MaxSea 2 t/gal
Week 3: MSU 1 t/gal, QO
Week 4: flush pots with water only
May
Week 1: MSU 1 t/gal, CM 1 t, refresh MB
Week 2: MaxSea 2 t/gal, CM 1 t
Week 3: MSU 1 t/gal, CM 1 t, QO
Week 4: flush pots with water only
June
Week 1: MSU 1 t/gal, CM 1 t, refresh MB
Week 2: MaxSea 2 t/gal, CM 1 t
Week 3: MSU 1 t/gal, CM 1 t, QO
Week 4: flush pots with water only
July
Week 1: MSU 1 t/gal, CM 1 t, refresh MB
Week 2: MaxSea 2 t/gal, CM 1 t
Week 3: MSU 1 t/gal, CM 1 t, QO
Week 4: flush pots with water only
August
Week 1: MSU 1 t/gal, CM 1 t, refresh MB
Week 2: MaxSea 2 t/gal, CM 1 t
Week 3: MSU 1 t/gal, CM 1 t, QO
Week 4: flush pots with water only
September
Week 1: MSU 1 t/gal, CM 1 t, refresh MB
Week 2: MaxSea 2 t/gal, CM 1 t
Week 3: MSU 1 t/gal, CM 1 t, QO
Week 4: flush pots with water only
October
Week 1: MSU 1 t/gal, CM 1 t, refresh MB
Week 2: MaxSea 2 t/gal, CM 1 t
Week 3: MSU 1 t/gal, CM 1 t, QO
Week 4: flush pots with water only
November
Week 1: MSU 3/4 t/gal, refresh MB
Week 2: MSU 3/4 t/gal
Week 3: MSU 3/4 t/gal, QO
Week 4: flush pots with water only
December
Week 1: MSU 3/4 t/gal, refresh MB
Week 2: MSU 3/4 t/gal
Week 3: MSU 3/4 t/gal, QO
Week 4: flush pots with water only
As a shorthand:
January, February, November and December (winter/resting months) have the same regimen.
March and April (slow growth months) have the same regimen.
May, June, July, August, September and October (robust growth months) have the same regimen.
I use this schedule for phalaenopsis, aerangis, angraecum, brassavola, bulbophyllm, cattleya, coelogyne, dendrobium, encyclia, epidendrum, laelia, leptotes, masdevallia, maxillaria, neofinetia, paphiopedilum, psychopsis, vanda, and a few other orchid genera. Of course, some demand longer, non-fertilized winter rest than others. I mark those pots with a colored tag to remind me not to fertilize them, and always use pure water sparingly in the cold.
I finally feel as though I've begun to crack the Rubik's Cube of orchid fertilizers and amendments. I remain open to new things, but for now, I like being able to trace my orchids' health through records of thoughtful care.
Happy growing!