pH for orchids
 

Most orchids grow best with a slightly acidic pH around their root zone. However, you really need to research the type of orchid you are growing & determine what their prefered pH is. I understand Paphiopedilums actually prefer a slightly alkaline pH.

The fertilizer must be water soluble within a specific pH range so that the roots can take the nutrients up. There are macro and micronutrients which are important for the orchid's growth. I fertilize my orchids in distilled water which, like R.O., does not contain minerals or has had the majority of them removed. For that reason, there is nothing in the water to act as a buffering agent so the addition of fertilizer can cause the pH to drop to very acidic conditions which are harmful to the orchid. When pH is too acidic, toxic amounts of the fertilizer can be taken up by the roots. When the pH is too alkaline (base), the fertilizer is no longer water soluble and is not available to the roots for uptake.

Over the years, I have seen recommendations of anywhere from 5.8 to 7.0 (acid to neutral) pH for growing orchids. It is my understanding that a pH level of 6.4 to 6.5 will allow the best nutrient uptake of the majority of macro & micronutrients. However, all substrates (I believe LECA is an exception) decay & become more acidic over time and I grow my Phals in sphagnum moss which is an acidic substrate. For that reason, I aim for a pH of 6.5 to 6.9 which is low acidity towards neutral. I have also read that some diseases become more prominent at lower pH levels. This has worked well for me growing Phals & Cattleyas under T5 fluorescent lighting indoors.

In the end you will need to begin periodic testing of your fertilizer solution after it has run through the substrate you are growing your orchids in. To start though, you should make sure the fertilizer going in is in an optimal pH range for the best nutrient uptake possible. After awhile, you'll find what works best for you.

I do use liquid MSU Fertilizer for pure water plus I add Humid Acid & Protekt to the mix. If you decide to switch to MSU let me know & I will tell you how much I was advised to use in the spring/summer and fall/winter. I do fertilize 'weakly' at each watering & flush with tap water twice a month. In the early spring. I will also add Cal Mag separately just to make sure my orchids are getting enough calcium & magnesium when their growth begins. I will only do this three times because I don't want them to receive too much.

I did find an article on the Venice Orchid Society located at: HOW YOUR WATER CAN AFFECT YOUR ORCHID – “PHood” – Venice Area Orchid Society. It stated that numerous white spots on your orchid leaves can also be caused by high alkalinity. Glad you ordered that pH meter. I think it will help you figure this out. Good luck!

Hey, excellent point there. Phal bellinas are probably as far to the "warm" of warm-growing as any of the Phal species. I had a similar problem with a compot of manii seedlings (also warmth lovers) and lost one of the three. I moved it to a warmer (rarely below 70), more humid growing area and it's showing signs of recovery. With the manii I have no doubt that a difference of 5-7 degrees has been important. My two bellinas (bellinae?) have always been in the same room and are growing furiously. Interesting, I have two or three violacea seedlings in the cooler area (my kitchen grow window) and over the past couple of months both have produced healthy, green leaves which have already doubled the size of their previous leaves; I would expect the violacea to want to grow where the bellinas are.

Tested the pH of my water with fertilizer and mag-pro and getting 6.42.

I guess I'll continue with the Magnesium and hope for the best.

Your setup looks great!

Water pH after mixing fertilizer is very dependent on what is in the water to start. A lot of dissolved minerals act as a buffer, minimizing changes in pH when acid or base are added. So it has to be tested for each municipal water supply or well.

As an example, putting collected rain into a planted, soft-water aquarium intended for fish from very low mineral content water (like South American tetras) gives a tank that rapidly becomes more and more acidic. Within 1-3 weeks the water would become too acid for the fish to live. This is because breakdown products of organic matter in the soil release a lot of acids. When I mix just 10% of my municipal tap water, with TDS 800-1200, with 90% rain, the dissolved minerals buffer the organic acids, and the tank maintains a stable pH.

A more detailed explanation of acid-base buffering is far beyond the scope of Orchid Board, but would make very interesting reading for those so inclined.

Hey everyone. So I have a new leaf and roots growing nicely on this one, but am noticing some cell collapse on other phals in my collection. Those plants had suffered some possible cold damage in the fall but nothing for the past few months.

I've definitively fixed all external factors including PH at this point and as I keep reading about this I'm really fearing this is a Virus.

The POTY Virus seems very similar to this, where new leaf develop normally, roots as well and then damage moves over to the new growth once it matures. I also read the cell collapse that looks related to cold damage can in fact be this POTY Virus. Seems to affect Phals very badly and read people losing entire collections. The only problem, is that none of those users ever confirm via tests if it was in fact POTY Virus. Everything always seems based on assumptions...

At this point, I'm thinking of trashing all plants with sympots... It's just unfortunate cause they are all in bloom right now :(. Most of them ill get over as they are complex hybrids... It will just make place for better plants :p But I really like my Bellina and don't want to trash it. Anyone has experience with POTY Virus?

I've added a photo of another Phal that has recent yellow spots that turned into cell collapse? Anyone has insight?? The left photo was after only a few days of the yellow spots showing up and the right one is 3 weeks later.

Thanks in advance
Emmanuel

Hi Manu,

I had this happen to a bellina of mine as well, and I'm sorry to say... Unfortunately, it died. :(

My understanding with cold damage and cell collapse is that you notice the damage after the plant is stressed by some factor, often months later, by heat or sun for example. This is what happened to mine, I believe.

I bought it from a vendor I no longer frequent, who put the bellina in a cold greenhouse (I'm not sure why, since they're warm growers.). I remember when I bought it that the leaves were lime green and actually cold to the touch. If I'd known more about bellinas (and the vendor) at the time, I wouldn't have purchased it.

The cell collapse didn't spread to the rest of my plants, though I think another of that vendor's plants died the same fate. If I remember correctly, it tried to grow new leaves, but as each leaf grew out it would show the same symptoms of collapse and die off. Eventually, I think the base of the plant turned creamy white and the whole thing died.

I hope you have a different experience. Good luck!

Sorry for the confusion the Bellina doesn't really have cell colapse, more chlorotic spots I'd say, photos are in the first post. The cell collapse is happening on 3 complex hybrids I have in the same growing area as the Bellina. Reading about chlorotic spots led me to think the Bellina could be virused with PhCSV aka Taiwan Potyvirus.. And then I started reading more about that and found that Potyvirus often may look as cold damage or cell colapse.. the last image is from a Phal V3 that started having yellow spots that quickly turned to cell colapse.my problem is that a full virus test is over 100$ and a new Bellina is 25$.. scrapping 3 hybrids and my Bellina would still be cheaper then testing it. I did the Agdia immunostrips for orchids on all 4 plants and results were negative.

Contact somebody in the botany or agriculture department at a nearby university and talk about it with them. They might be interested in trying to identify the problem under a light or scanning electron microscope, or via immunologic means.

Universities here have agricultural extension facilities intended to help farmers and the general public with things such as this. A lot of people take unusual insects to Arizona State University for identification, for example. And the University of Arizona has a facility in each Arizona county with agricultural agents available to the public.

Manu, this now looks like sunburn damage to me. You can see the damage beginning as a patchy yellowing in the left leaf that leads to the dead tan section on the right leaf. Too much light can cause orchids leaves to yellow which might actually have been the cause of the mottling discoloration you initially reported.

Sunburn on an orchid leaf does not always look the same. Sometimes you get yellowing leaves, tan patches, black patches or black spots.However, I have seen photos of leaves like your photo on the right which were identified as sunburn.

If the light is not reduced, the damage will continue and will result in a permanent scar on the leaf as your leaf on the right has. If your other phals are receiving the same amount of light, this might explain why they are developing the same symptoms. If you correct the lighting before permanent damage to the leaf occurs, the leaf will return to its normal color.

Try going to this site on 'Environmental Damage' to orchids:

Orchid Environmental Damage

There is a section in the list for nutrient deficiencies, cold damage and sunburn as well as other problems. There is a link in each section you can click on which shows additional photos. Click on the link under sunburn & you will see a photo with the same tan patch in the leaf as yours has.

I really don't think this is a virus. Try raising your lights or lowering your plants. Let us know if there's any improvement.

That's a great idea! I'll try to ask the Montreal Botanical Garden for guidance.

---------- Post added at 02:43 PM ---------- Previous post was at 02:34 PM ----------

Hi Sharon

I wish I could attribute this to sunburn... It starts on leafs in the middle.. so there are leafs getting much more light above and unaffected, yet.