Hi Mike, I have never found one. The yellowing habit and lime cure happened with my globulosa. After that I have decided to add a few teaspoons in a three gallon batch of soil. If the globulosa starts up again I sprinkle a bit into the pot and it recovers as you described. ~ Mary

There are Hoyas that grow in areas that overlie limestone formations but in relation to the overall number of species their numbers are small. Often times plants that grow in these habitats are found only in conjunction with limestone. The interesting part is that most Hoyas are epiphytes so they would have limited direct exposure to limestone. If a plant is lithophytic (growing on rock) or terrestrial and growing in coral sand based soils then it would experience much higher levels of calcium carbonate. Calcium carbonate rich soils result in iron and phosphorus being made less available to plants as a result of the higher pH. The adaptations the calcium loving plants have to their environment means that you need to provide for their specific needs in culture to really be successful.
It is not a good idea to add calcium carbonate, dolomitic lime, or limestone chips to just any plants potting mix as many plants have an aversion to high calcium levels.

Generally speaking many of the Eriostemmas are said to like higher pH environments. Hoya imperalis is another that enjoys added lime.

I always use Epsom salts to help a yellowed plant produce more chlorophyll and I find that it works very well.

Mike

I have a few Hoyas - mostly the Eriostemma types that have leaf yellowing at times. When that happens, I just sprinkle a very little bit of Calcium Nitrate on top of the pot and water it in. Specifically the imperialis, the ciliata and coronaria do this. The yellowing stops after I water in the CaNO3.

And two separate issues, do they like the higher pH? or do they like the extra Calcium?

Renee

Renee the two go hand in hand. I think a great approach might be to use crushed oyster shells in the mix to have a slow leaching of Calcium. This would make a nice chunky and fast draining mix while keeping the pH and calcium at levels where the plants are happy.

Mike

Mike,

What I'm very badly attempting to say is, that we don't know if it is Ca or basicity. Because Ca containing products don't have to raise pH, and you can raise pH without Ca.

I don't recall ever seeing anything that determines if it is the combination, or just extra Ca or just higher pH.

All I know is that when I'm using the high Calcium fertilizer (acidic pH) I don't get the yellowing leaves problem. And when I can't fertilize (6 weeks of rain) CaNO3 which is not basic stops the yellowing of the leaves.

That is what leads me to question whether it is high pH, or extra Calcium or a combo?

Does this explain what I mean better?

Unfortunatley oyster shells wouldn't work for me, I don't grow in media that would retain them. Although I do have to say oyster shells are pretty much free around here :)

Renee

I guess I was thinking more of natural systems than of horticultural practices. Plants would be much more likely to encounter limestone and not Calcium Nitrate. It must be different for each species as some might only need a higher pH to do well while others would need a high calcium environment. I will see if I can dig up any good articles on the subject. If anyone finds something of interest please post it.

Do you buy dry chemicals and mix your own fertilizers? Perhaps I should invest in some Calcium nitrate as I currently only have dolomitic lime on hand.

Mike

Mike, No I don't mix my own, but last summer I was having Ca deficiency showing in some of my orchids.

Problem is most fertilizers for tap water don't include Ca as manufacturers assume there is enough in tap water. Well I called our water department, and our water is really really good. Very little Ca. Plus my plants get a lot of watering during the warmer months from rain - again no Ca. So I bought some CaNO3 to supplement. I have since switched fertilizers to one that contains a lot of Ca - so I don't need to add the CaNO3 anymore, but I still have it around.

So with the constant rain occurring this summer, I haven't been able to fertilize as often as I should, so the ones that seem to need more Ca, I just took a pinch and put it in the pot. Completely unscientific, but it stopped the yellow leaf issue.

Renee

Still it's all very good info for us. The causes of yellowing leaves are potentially quite diverse but knowing the possible solutions is half the battle.

Mike

I think the Ca/Mg vs pH question is a very good one. My guess is that Ca and/or Mg is the important factor. Many people suggest adding lime to Eriostemmas, but I don't. My tap water has very high Ca and alkalinity levels (possibly Mg as well, though I haven't tested for that). I add almost 2 Tbs of vinegar per gallon to neutralize the alkalinity of my tap water, plus a fertilizer containing Ca and Mg, and this is what I use to water my Eriostemmas and other Hoyas. So they get lots of Ca/Mg, but the pH is only around 5.8 (the value at which all alkalinity should be neutralized). My Eriostemmas have deep green leaves and have grown to the top of my greenhouse, so high pH does not seem to be a requirement for them in my case. The high Ca/Mg levels in my tap water plus fertilizer may be benefiting them, though.

-Chris

Chris I think one thing that far too few people do is investigate their tap water. Water can come from so many sources and they all result in significant changes in the mineral composition or lack there of.
If you are using a well then chances are that you might be fine to not add anything to the water or the potting mix. Still different areas of the country very greatly in geology and that affects the mineral content of the water as well.

Maybe one of the first things everyone should do is look for info about the water they use. Look for municipal web sites etc where this info should be available.

Chris thanks for mentioning the Ca/Mg fertilizer as that is another option for people to use with these types of plants. Do you use the fertilizer at every watering and then supplement the N-P-K on a schedule?

Mike

OK after doing some of my own checking I will elaborate further on the lime I have been using. Barn lime which I learned is calcium carbonate a non caustic lime, was used by my family in chicken coops.

Dolomite lime/hydrated lime had too much magnesium not good for egg production. The goal there being balancing ph to reduce ammonia on the coop floor and strengthen the eggshells in feed. As it does little harm for breathing it in as hydrated lime this was the standard for the animals safety.

I had purchased garden lime as it was labeled from my local garden center and mixed it with water. Since this created an additional watering practice I switched to the barn lime we had already used in the yard for the lawn. The goal there being balancing ph from pines and black walnut. I could safely sprinkle it in on individual plant pots as the need arose plus mix it with soil batches.

From the perspective of persons who raise horses neither of these two limes do much to eliminate ammonia rates they are trying to reduce and come right back to where they started. The commentary was that hydrated lime actually contributed to the ammonia production at a faster rate than the barn lime. Mike are you proud of me for being more scientific, you know it is not my forte! I certainly like the suggestion from Chris regarding the vinegar. Answers for Renee I don't know. I have concluded that I have no plans to clean barns! ~ Mary

Yes, water chemistry can vary greatly. I'm using municipal water, but it comes from a number of wells so the mineral levels are, apparently, quite high. At first I was disappointed to discover this because I have to use RO water on my mounted epiphytes to prevent damaging sensitive species, and to prevent mineral deposits all over the plants and greenhouse. But it may be a good thing for some of the Ca/Mg loving plants.

As for fertilizer, I use Dyna-Gro's Foliage Pro 9-3-6 at every watering. It supplies N-P-K plus Ca, Mg, S, and micronutrients. I've also used Botanicare's Cal-Mag Plus, which is good if you really need to boost Ca/Mg, but now I just use the Foliage Pro and tap water. Lime is a very easy solution that probably works quite well in most cases, but I worry that many species may simply be tolerating the increased pH and not necessarily benefiting from it. It also releases Ca and Mg in different proportions as it dissolves, and there is no way to be sure of when it's exhausted. By supplying Ca/Mg in the water rather than the soil, I know that my plants are getting exactly what they need at every watering. Maybe I have a bit of OCD in this respect, but it keeps my mind at ease and seems to be working well. :)

-Chris

Yes we have a farm\fleet store by us and I will look into that also. I never heard much but slang with regard to the lime in family farm discussions such as sweet sour and to stop it from smelling like.... Also to make white wash. TKX ~ Mary

I think Ted Green's website (I think it's rarehoyas.com) does a good job listing if a species needs lime.
Randy

Is it possible that the potted Hoya's roots are pot bound and need to be repotted? That is what I just did to my Hoya Carnosa....as some of my leaves were starting to show some yellowing. Now i have another Hoya in another room, use the same water and never had any yellowing there. I repotted that too about a couple of months ago, not because it was showing signs of yellowing, but it was really pot bound. Its been years since I repot Hoya's, cause they suppose to thrive on it.

Thanks so much everyone!

I have been reading this and trying to understand it a lot. I really appreciate the time you spent here with me, and MIke, in my eyes, the pro at Hoya, thanks again!

Mike

Just saw this quote and thought it was relevant here.

Al (tapla) from another thread: "Well, you would think that because garden lime (dolomitic lime) has a solubility of about 1/3 oz/100 oz of water and is comprised of both CaCO3 and MgCO3 (calcium and magnesium carbonate) that they should become available in the same ratio as the dolomite dissolves. The fact of the matter is that the CaCO3 fraction of the lime has a solubility of about .0015, while the MgCO3 fraction is soluble at a rate of about .175, or roughly about 125X more soluble than the Ca fraction.

With dolomite being about 20% Ca and 10% Mg, you would also think that they would be released in about a 2:1 ratio, but what actually occurs is: at first, during the first few months, the release rate is about 1:1 or a little greater, then slowly shifting to around a 2:1 release at some point in the soil/planting's life, and then after 9 months to a year to 2:.05 or even less. This issue can be very acute for plants grown in the same soil for more than a single growth cycle."

It sounds like lime use may result in a Mg deficiency when used beyond a single growing season. Since lime is used in practically all peat based soils, this may be one reason that some people see an improvement when adding epsom salt (MgSO4) to their water. This is also one reason I think it is better to supply these minerals in water soluble forms rather than lime when growing perennial plants like Hoyas.

-Chris

Chris thanks for that information. It does seem that using a water soluble product as part of regular fertilizer applications would be best. I don't think any of us are repotting our Hoyas frequently so using a standard mix makes so much more sense. Just tailor the fertilizer and mineral supplementation to suit each plant.

Mike