Lime is used to supply calcium and magnesium in acidic potting mixes such as those predominantly peat or pine bark based. Lime is used because it raises the pH to a more favorable value while also supplying these two nutrients.

When using potting mixes that aren't acidic lime is generally not used. The pH changing affect of lime isn't wanted. A source of Ca and Mg is still desired. For this reason it's common to add powder/granular gypsum to the potting mix. It's added to the mix directly because it is not particularly soluble in water and releases Ca over time.

Gypsum doesn't contain any magnesium, however. Both Ca and Mg are often missing from fertilizers, particularly water soluble ones so the use of epsom salt (magnesium sulfate) is done when fertilizing plants. It isn't added directly to the mix because it is very water soluble. Adding it to the mix would see it run right out with a watering or two and it only added when fertilizing (it's simply adding nutrients to the water that many fertilizers lack).

You may wish to read Al/Tapla's post on the container gardening forum about fertilizing in containers for more information.

Great explanation jag!!

And the time you took out of your busy schedule to explain this to us was very kind of you..;-)

Yes, thanks for the info. I just got back from a two week vacation in NY to the terrible heat and humidity of FL. I am happy to report that all my citrus looks pretty good. I have new growth on my new Meyer lemon and persian lime (in the gritty mix). I think we had a lot of rain while we were gone so I am happy that I had a fast draining medium.

So let me see if I have this straight...

The gritty mix is not "predominantly peat or pine based" since it is only 1/3 pine based. Therefore, I don't need the lime but I still need the Ca and Mg. I can get the Mg from the epsom salt while watering. How can I get the Ca to my plants? It is not in the MG water soluable fertilizer I am using in a very diluted form when I water.

If gypsum is the answer, could you tell me a brand name or how it is packaged? I think I could get some into the mix even though the tree is already potted.

I saw a post (I think from JAG) about citrus being a challenge to grow. I'll say! I am anticipated my first 12 lemons this fall after three long years of babying my in ground tree. Hopefully, it will all be worth it!

Tammy

So let me see if I have this straight...

The gritty mix is not "predominantly peat or pine based" since it is only 1/3 pine based.

Correct. Therefore, I don't need the lime but I still need the Ca and Mg.

Correct. The lime will supply the calcium and magnesium just fine, but it will also raise pH which is not desirable unless the mix is initially too acidic for strong plant growth. I can get the Mg from the epsom salt while watering

Correct. Epsom salt is magnesium and sulfur so by using it both are being supplied to the plants. How can I get the Ca to my plants?

With gypsum. Gypsum is calcium and sulfur. It's not particularly soluble in water so it's very slow release. This is why it's added to the mix rather than to the fertilizer water. If gypsum is the answer, could you tell me a brand name or how it is packaged? I think I could get some into the mix even though the tree is already potted.

Yes, you can get it into the mix by simply scratching it into the top few inches. If you have a store nearby that sells Espoma products you can find it under that brand. It's just a 5 lb bag (which will last for many containers). If you look at hardware stores in the garden section you will likely find 50lb bags of it for around the same price. Lot's of folks pay the premium for the Espoma brand because it's common these days in garden centers and they can trust it's what they need. The hardware store bag is a much better value though and has no shelf life so can be stored indefinitely. Your call. I saw a post (I think from JAG) about citrus being a challenge to grow. I'll say! I am anticipated my first 12 lemons this fall after three long years of babying my in ground tree. Hopefully, it will all be worth it!

I am by no means a citrus expert. I live in Wisconsin and started with citrus only in containers a couple years ago. I also don't consider citrus particularly challenging in the sense of keeping them alive and growing. I do consider them patience trying in the sense that many people purchase citrus or other fruiting trees and in the back of their mind they think of them as a tomato ;) Plant them and by the end of the 1st season there should be a large harvest.

Not typically the way it works ;)

I am growing citrus for the change in pace from the stuff I usually grow. Not because I am in a hurry to make lemonade or fresh squeezed orange juice. That's probably a good thing or I would be really ticked off about now ;)

AWESOME! I am off to get some gypsum in the morning.

Out of curiousity, do your container citrus currently bear fruit? What kind of yield do you get from a container (lime), for example, once they finally get to fruit bearing age?

Thanks for all the info and sorry for the typos and misspellings...

I posted a fairly lengthy reply that I must not have fully submitted as it isn't showing up.

The condensed version is that I have only grown citrus for 2 years so while some trees do bear fruit, it isn't much and some have yet to bear anything (or even flower).

I live in Wisconsin and unless one travels further north it would be hard to find a less citrus friendly climate. I don't expect the trees to bear prolifically in year one, or two or three. I have fruit bearing trees adapted to my climate in the ground that didn't bear at all for a few years and even now that they are bearing what they produce is nothing compared to what they will do 5 years from now.

Trees are not for those who want harvest/yield this year. Trees are for those who value the tree for what it is and look forward to harvests years down the road assuming cultural parameters are all reasonably met.

Just incase you don't find the gypsum you are looking for, try using a fertilizer that supplies all your needs, including mag and calcium such as "foiliage pro" by dyno gro...GREAT STUFF

This is the best fertilzer I have ever seen, as suggested by both Al na Jag.

And if you do find the gypsum,you can still feed with foiliage pro, knowing it is supplying what other fertilizers do not until the gypsum kicks in..:-)

My citrus all produce lots of fruit in containers..Thanks to Al and Jags suggestions on the gritty mix.. Here is the proof..

Good luck!:-)

http://forums.gardenweb.com/forums/load/fragrant/msg0618190628545.html?6

jag what are you talking about?
You of all people can grow citrus if you wanted to. I live in New England, a much less than friendly enviroment for my trees and they all produce very well..

I had a orange navel that produced 8 full grown juicy seedless oranges, limes, lemons and so on, and yes in the gritty mix.

Did you see the grapefruit I am growing..lol

It can be done, and I know you can do it..:-)

Thanks for the vote of confidence, Mike ;) I am sure I can grow them (I am growing them ;), but fruiting prolifically is something the trees do when they are ready to do so, not on my timetable or I would have a loaded fruit drawer in the fridge already ;)

lol..:-)