Adjusting the pH of your water is a way to improve your orchid culture and squeeze the last 10% out of your plant’s potential. From phalaenopsis and oncidiums, to phragmipediums and paphiopedilums, pH might not be something you have to mess with, but in this post I’ll cover the many reasons why you might consider it.
Before I get into the details, the below graphic that really sets the stage for why pH adjustment is valuable to orchids. It illustrates nutrient and mineral solubility and the relevance to orchids. I’d like to instill this caveat: not all orchids need the exact same pH. Depending on the species of orchid you’re growing, it will have adaptations to habitats that may have different pH. However, the majority of orchids we keep are epiphytes and have adapted to rain water which has an acidic pH of 5.5 due to carbonic acid (from CO2), and those orchids will fall into the range noted in the graphic.
Orchids are beloved for their exotic, delicate blooms that add elegance to any space. But cultivating these captivating plants requires meeting their particular needs. One key factor is pH – the relative acidity or alkalinity of the potting environment. This raises the question: are orchids uniformly “acid loving” plants? Or do they have diverse pH requirements?
The answer is nuanced. While many orchids thrive in acidic conditions, others originate from more alkaline habitats. There is no single optimal pH for all 25,000+ orchid species and hybrids. Understanding your particular orchids’ native conditions provides clues about their ideal pH range. This allows you to tailor care accordingly.
Examining pH in an Orchid’s Native Habitat
To determine whether an orchid naturally grows in acidic or alkaline environments. consider
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Where it grows – epiphytic on trees, lithophytic on rocks, or terrestrial in soil?
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The native geology – sandstone. limestone. basalt?
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Its proximity to water sources – soft rainwater or mineral-rich runoff?
The habitat provides hints about suitable pH levels. Mimicking those natural conditions often benefits orchids.
Major Orchid Types and Their Preferred pH Levels
Epiphytic Orchids
Epiphytes like phalaenopsis, cattleya, and oncidium grow perched on trees. Their native pH is influenced by:
- Rainwater (naturally pH 5.5-6)
- Decaying organic matter (releases acids)
They thrive best in a mildly acidic pH around 5.5-6.5.
Lithophytic Orchids
Lithophytes like phragmipedium, paphiopedilum, and vanda cling to limestone outcrops. Here, the pH trends neutral to alkaline (7-8) due to:
- Buffering from calcium carbonate in the rocks
- Hard water runoff
Terrestrial Orchids
Terrestrials like cymbidium and calanthe grow in soil. Their ideal pH varies based on the native location:
- Sandy, acidic soils – low pH below 5.5
- Limestone terrain – alkaline pH around 7-8
- Tropical forest floors – acidic humus pH around 5.5-6.5
Signs of Improper pH
Orchids will show signs of distress if their pH needs aren’t met:
Symptoms of High pH
- Smaller leaves
- Leaf tip burn
- Reduced flowering
- Nutrient deficiencies
Symptoms of Low pH
- Yellow lower leaves
- Slow growth
- Root loss
- Iron toxicity
Monitor plants and adjust pH accordingly if any issues arise.
Best Practices for Watering Based on pH
Tailor watering practices to match your orchids’ preferences:
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Use rainwater for orchids preferring low pH.
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Use hard tap water for orchids wanting neutral/alkaline conditions.
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Acidify tap water for acid-lovers.
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Add limestone to increase pH as needed.
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Flush pots regularly to prevent buildup.
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Ensure excellent drainage.
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Test pH routinely to optimize conditions.
Adjusting pH
To lower pH:
- Use diluted citric acid or phosphoric acid
- Add sulfur or acidic peat moss
To raise pH:
- Add dolomitic lime or crushed oyster shell
- Use hard tap water
Go slowly and check pH frequently to prevent overshooting the target range.
The Takeaway
Rather than assuming all orchids require highly acidic conditions, consider their native habitat. This provides clues to tailor pH and cultivation practices to support healthy, vibrant plants. Paying attention to individual needs allows you to unlock every orchid’s full potential.
There ARE Orchids that do Better With a Higher pH
This isn’t a question–it’s fact. That’s why people add limestone to many orchids to improve growth.
Orchids that do better with higher pH are lithophytic and terrestrial species native to the Malaysian Limestone Region (Malaya, Sumatra, Java, Sulawesi and Borneo), as well as orchids from the mountain base of South America (Peru, Ecuador, etc), and any other orchids that grow in, on or around mountainous areas with exposed limestone, basalt or marble (often areas that are close to waterfalls and rivers). Areas where the water is buffered up by the presence of calcium carbonate in the rocks and subsequently in the water table as well.
Which Orchid Species Do Better with a Higher pH?
Orchids from the above-mentioned regions of course! And likely hybrids of those species.
Examples of High-pH Growing Orchid include:
- Phragmipediums (besseae, fischeri, kovachii, schlimii, caudatum, caricinum, boissierianum, longifolium, warscewiczianum (syn wallisii), and pearcei),
- Phalaenopsis (maculata, modesta, fimbriata, sumatrana, lowii, corningiana, pulcherrima, braceana, viridis, and cochlearis),
- Paphiopedilums (armeniacum, bellatulum, stonei, sanderianum, lowii, esquirole…and many other Chinese paph species),
- Rupicolous Laelias (bradei, briegeri, lucasiana, esalqueana, milleri, etc)
- Vanda suavis tricolor
- Ludisia discolor and other “jewel orchids” from the above mentioned regions.
There are likely many other species (and don’t forget to include hybrids of those species) that will prefer higher pH, but at this point I’m still researching and exploring those specific orchids from those regions (which are of course not exclusively epiphytes). I will append this document as I find other species that prefer high-pH.
How To Feed Your Acid Loving Plants
FAQ
What does Epsom salt do for orchids?
What houseplants are acid loving plants?
Common acid-loving plants
Ceanothus, Japanese anemones and Pieris japonica are also great choices for acidic soil. All can even be grown in containers, so if you don’t have acidic soil but love these plants, you can still grow them in the right compost.
Do orchids like coffee grounds for fertilizer?
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Potential Benefits:Coffee grounds contain nitrogen, which is a crucial nutrient for plant growth, and some suggest they can be a source of other beneficial nutrients for orchids.
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Potential Risks:
- Molding and Rot: Coffee grounds can decompose quickly, leading to mold and rot in the orchid’s growth medium, which can damage the roots and lead to disease.
- Nutrient Imbalance: It’s difficult to control the exact amount of nitrogen and other nutrients provided by coffee grounds, potentially leading to imbalances that can harm the orchid.
- Acidic pH: Coffee grounds can lower the pH of the growth medium, which may not be ideal for all orchid species, according to HGTV.
- Molding and Rot: Coffee grounds can decompose quickly, leading to mold and rot in the orchid’s growth medium, which can damage the roots and lead to disease.
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Better Alternatives:Using specifically formulated orchid fertilizers is generally recommended, as they provide balanced nutrients and are less likely to cause harm.
Do orchids like acidic soil?
Yes, orchids typically prefer acidic soil with a pH of 5.0 to 6.5. In general, they grow best in soils that are slightly acidic or neutral. To maintain the ideal soil pH for orchids, you can add peat moss or bark to your potting mix.
Do plants like acidic soil?
Sharing is caring! Acid loving plants are all around us. From fruit to flowers, shrubs to trees, lots of garden and landscape favorites thrive in acidic soil. Plants that like acidic soil tend to do well with acid fertilizers and other soil additives that help to bring down the pH to the acidic range.
Do orchids have a different pH?
Depending on the species of orchid you’re growing, it will have adaptations to habitats that may have different pH. However, the majority of orchids we keep are epiphytes and have adapted to rain water which has an acidic pH of 5.5 due to carbonic acid (from CO2), and those orchids will fall into the range noted in the graphic.
What soil do Orchids need?
When it comes to orchids, there is a wide variety of plants and their soil requirements can vary greatly. Generally, orchids prefer to be planted in soil that is slightly acidic, with a pH of 5.5 to 6.5. However, some varieties of orchids, such as Phalaenopsis, prefer a more acidic soil, with a pH of 4.5 to 5.5.
What pH do Orchids need?
This is a hotly-debated topic online with hobby orchid growers assuming, 5.8 pH is the magic pH, where you get optimum nutrient availability and uptake in orchids; however, I call bluff on the necessity of that exact pH for all orchids.
Are blueberry bushes acid loving plants?
Blueberry Bushes are Acid Loving Plants! What Soil pH Do Acid Loving Plants Need? Acidic plants tend to need a soil pH of around 5.5. Some acid lovers may do well all the way down to a pH of 4.5. The lower pH of 4.5 to 5.5 allows the acid loving plants to better absorb the nutrients from the soil. Slightly acidic soil improves nutrient access!