MSU orchid fertilizer is a water soluble fertilizer formula developed at Michigan State University. It was built to solve a specific problem.
Most fertilizers assume tap water with no minerals in it. Real growers use rainwater, reverse osmosis water, well water, or hard tap water.
The formula came out of research on African violets. It later proved itself with orchids too. One documented Cymbidium collection fed with it earned repeated American Orchid Society awards.
Those awards came over six or seven years. Plants scored as high as 91 points, a strong result for the genus. That track record is why the formula still gets recommended decades later.
What MSU Orchid Fertilizer Actually Is
MSU orchid fertilizer is not one product with a single number. It is a nutrient program with two distinct formulas. Each one is built around a different water source.
Growers choose the version that matches what comes out of their tap. Both versions skip urea as a nitrogen source. Urea needs soil microbes to break it down first.
Soilless orchid mixes do not have that microbial activity. Instead, both versions rely on nitrate and ammonium nitrogen. Orchid roots can absorb these forms right away.
This design sets MSU orchid fertilizer apart from many all purpose plant foods on a typical orchid fertilizer ranking. Most of those products use whatever nitrogen source is cheapest. The MSU program was built around what orchid roots can actually use.
The Two MSU Orchid Fertilizer Formulas
The reverse osmosis and rainwater version is labeled 13-3-15. It carries added calcium and magnesium. Pure water supplies none of those minerals on its own.
The well water and tap water version is labeled 19-4-23. It still contains calcium and magnesium, but less of it. Typical tap or well water already carries some mineral hardness.
Confusing the two versions is a common mistake. The RO formula with hard tap water leaves plants short on nitrogen and potassium. The tap formula with pure water can undersupply calcium and magnesium instead.
Genus matters too. Phalaenopsis in bark tolerates either MSU version well, since bark itself holds few minerals. Cattleya and Dendrobium in bark behave the same way.
Vanda grown bare root in baskets often needs the stronger tap water version. Frequent watering washes nutrients out fast in that setup. That makes the extra nitrogen and potassium useful.
How to Mix MSU Orchid Fertilizer
The standard orchid rule is quarter to half label strength. MSU orchid fertilizer follows that same rule. The table below shows a common starting point for each water type.
| Water type | MSU version | Typical rate | Frequency |
|---|---|---|---|
| Distilled, reverse osmosis, or rainwater | 13-3-15 (RO/Rain) | 1/4 to 1/2 tsp per gallon | Weekly |
| Soft tap or well water, under 525 ppm TDS | 19-4-23 (Well/Tap) | 1/4 to 1/2 tsp per gallon | Weekly |
| Hard tap water, over 525 ppm TDS | Neither version alone | Test water first | Not applicable |
One documented mixing example used about 2 teaspoons per 5 gallons of water. That mix went on at every watering, not just weekly. It is a stronger, more frequent approach than the common quarter to half strength method.
Growers sometimes call the weekly version the weakly weekly method. A dilute dose goes on at nearly every watering instead of a strong monthly dose. This mimics how orchids absorb nutrients in the wild.
Either schedule can work well. Just keep the total monthly dose in a similar range either way. Do not run both approaches at full strength at once.
A cheap TDS meter makes this easier to track. Test your tap water once before choosing a version. It takes only a minute and removes most of the guesswork.
For the full mechanics of a feeding routine, see how to fertilize orchids. That page covers timing and seasonal changes in more depth than fits here.
Why It Includes Calcium and Magnesium
Nitrogen, phosphorus, and potassium are mobile nutrients. When an orchid runs short, older growth shows the problem first. The plant pulls those nutrients from old leaves to feed new ones.
Calcium behaves differently, since it cannot move within the plant. A calcium shortage shows up in new growth instead. It often appears as weak or distorted leaves and buds.
Calcium and magnesium also need to stay balanced with each other. Dolomitic lime is a reliable source of both. MSU orchid fertilizer builds that balance into the formula itself.
That is one reason it holds up well against products that only cover NPK. For more on how ratios compare across brands, see this NPK ratio breakdown. It lays out the tradeoffs in plain terms.
Who Sells MSU Orchid Fertilizer
Greencare Fertilizers manufactures the MSU formula under license from the university research. Specialty orchid suppliers repackage and sell it. rePotme and Bloomerang Orchids both carry it.
This page contains affiliate links. If you buy through them, Orchid Reference may earn a commission at no extra cost to you.
The MSU Orchid Fertilizer 13-3-15 RO/Rain/Tap Water Formula ships in the RO and rain water version. That is the one most home growers reach for. Check the bag label first if your water is hard tap water.
When MSU Orchid Fertilizer Is the Wrong Choice
Hard tap water paired with the tap water formula is the main failure case. Both are already contributing calcium, magnesium, and dissolved solids. Stacking them can push total dissolved solids too high.
Water under 525 ppm of dissolved solids is generally fine for most orchids. Water near 175 ppm is closer to ideal. Above that range, flush the pot with plain water every two weeks to a month.
For a full comparison of water sources, see this guide to orchid water quality. It explains what each water type changes about fertilizing.
Never use a water softener that adds sodium ahead of MSU orchid fertilizer. Softened sodium water kills orchids over time. That holds true even when the fertilizer itself is correct.
Signs of Fertilizer Burn
Fertilizer burn from overuse shows up as blackened or crispy root tips first. New leaves may also develop dark tips or edges. The damage tends to spread from there.
Cutting the dose back to quarter strength usually stops further damage. Flushing the pot with plain water helps too. Recovery in new growth typically takes several weeks.
Thin leaved genera like Oncidium show burn faster than thick leaved Cattleya. A monthly plain water flush prevents most burn cases before they start. Skipping fertilizer for a month rarely hurts an orchid, but overfeeding often does.
If you are seeing weak new growth on top of burn signs, a magnesium shortfall could be layered in. Epsom salt for orchids covers when a separate supplement helps. It also covers when it just adds unnecessary salts.
Sources
- American Orchid Society: Fertilizer, orchid care guidance. https://www.aos.org/orchid-care/fertilizer
- American Orchid Society: A New Fertilizer Without High Phosphorus Proves Itself with Orchids. https://www.aos.org/a-new-fertilizer-without-high-phosphorus-proves-itself-with-orchids
- Clemson Cooperative Extension, Home and Garden Information Center: Orchids factsheet. https://hgic.clemson.edu/factsheet/orchids/
Frequently asked questions
What is MSU orchid fertilizer?
MSU orchid fertilizer is a water soluble fertilizer developed at Michigan State University for growers using pure or hard water. It comes in two versions matched to different water types. Both include added calcium and magnesium.
Is MSU orchid fertilizer a bloom booster?
No, MSU orchid fertilizer is a balanced growth formula, not a bloom booster. It does not carry the high middle number that bloom boosters use. Bloom boosters are optional and have not been shown to be necessary.
How much MSU orchid fertilizer should I use per gallon?
Most growers mix 1/4 to 1/2 teaspoon per gallon of water, applied weekly. That follows the general orchid rule of quarter to half label strength. Always check your specific package label first.
Can I use the RO version of MSU orchid fertilizer with tap water?
You can, but it skips the extra calcium and magnesium the tap version adds for water that already carries some hardness. If your tap water tests hard, the RO version plus a magnesium supplement often works better. Testing your water first removes the guesswork.
Where can I buy MSU orchid fertilizer?
Greencare Fertilizers manufactures the formula, and it ships through orchid suppliers like rePotme and Bloomerang Orchids. It also shows up on Amazon in both powder sizes. Check the label to confirm which water version you are getting.