Since no plants use N, P, and K in THE 1:1:1 RATIO supplied by 20-20-20, you can do better. Supplying fertilizer in the ratio at which your plants actually USE the nutrients offers some significant advantages, not the least of which is the ability to keep the level of dissolved solids (fertilizer/mineral salts) at their lowest w/o having to suffer the effects of deficiencies. After the calculations are done for how P and K are reported on fertilizer packages, you'll find that 3:1:2 ratio fertilizers like 24-8-16, 12-4-8 (Miracle Grow makes All Purpose fertilizers in these NPK %s) or 9-3-6 supply NPK at almost exactly the ratio at which the average plant uses the nutrients. I use Foliage-Pro 9-3-6 by Dyna-Grow almost exclusively for that reason and others, which include the fact that FP 9-3-6 includes ALL essential nutrients plants normally take from the soil (including Ca & Mg which most soluble fertilizers lack (MG 20-20-20 lacks these elements/nutrients) and FP 9-3-6 gets most of it's N from nitrate sources and no N from urea. The later fact helps keep plants compact and full. Also, your nutrient supplementation program is usually dictated by your soil choice and watering habits. Soils that retain too much water (like most off the shelf brands) require much more attention to detail than soils that you can water freely w/o concern that the soil will remain soggy so long it impacts root health/function. Root health is a key factor that determines whether or not a healthy organism is even possible - to the degree that good root health is a prerequisite to a healthy plant. Never apply Epsom salts willy nilly, that is to say w/o good reason. Unless it has been determined your plant is suffering a Mg deficiency OR there is an excess of Ca in the soil causing an antagonistic deficiency of Mg, you're probably 10X more likely to create limitations than resolve them by adding Epsom salts. You might find this Basic overview helpful. It will help you avoid all of the most common issues all container gardeners encounter early in their journey toward greater proficiency. Al

Goodmorning everybody! Actually Jean is most likely on target since most of the time she is. I tend to side with her on this. That very same thing happend to mine a few years back when I put a couple of mine on my hot flat roof, especially after a cool period. Within one day the leaves turned like that. As for over fertilization? The damage to the plant would always start on the leaf tip and then onto the margins. They would either turn brown or yellow and recede back further. Also you can get sudden light green compacted growth in the full sun which then declines rapidly. I would of actually thought it was fertilizer spray damage, but you don't fertilize this way. You can grow a plant in pure sand, if you fertilize almost everyday, so I am going to guess if anything, that plant is not fertilized often enough even with the slow release osmocote in the mix. If the weather gets too hot, it doesn't work, and if it gets too cold, it does nothing for your trees which is exactly what you described. Your fertilizing regimend is very good as long as the temps cooperate. You may still have root issues going on with that one if root damage was a problem as recently as the last few weeks. It can take a long time for recovery. Ps. Nothing wrong with spraying your plants down as often as you want with water any time of the day and in fact it is much welcomed for everyone one of mine:-) For some reason I just don't make it a practice to spray mine after dark. Mike

Now that I have learned to grow citrus with no problems I have 3 Poncirus trifoliata of grafting size and 4 sweetlee tangerine trees of vigor that will be graft-able next spring. That's 7 root-stocks that I can graft my twigs from the grafted tree I can purchase. My purchased tree will grow faster by waiting a year and will out grow anything I bought a year earlier. My decision is to not buy a grafted tree and to grow what I have. If it fruits, great If they don't. Well we'll see My from seed Nagami kumquat for grafting to poncirus trifoliata Seed grown Meiwa kumquat tree. The tree fruit I am interested in. To be grafted on to the poncirus trifoliata moots through the Nagami inter-stock. May also go directly to my sweetlee tangerine tree root-stock, Seed grown sweetlee tangerine tree for root-stock #1 Seed grown sweetlee tangerine tree for root-stock #2 Seed grown sweetlee tangerine tree for root-stock #3 Seed grown sweetlee tangerine tree for root-stock #4 Seed grown poncirus trifoliata to be grafted on Is posted above . Its in a blue 55 gallon half drum. This completes what I have done and what I have. If I think of anything I'll add on to this thread Steve This post was edited by poncirusguy on Tue, Nov 5, 13 at 18:29

You have to be careful about ratings for the citrangequat of 'survived 5F' etc. (or any other subtropical broadleaf evergreens grown in the south - or various 'hardy palms' for that matter) They might have survived 5F somewhere down south where the 5F was a single night and within a couple days the average temp was back above freezing. I had a citrangequat freeze to death in the Polar Vortex winter here in "7a", after hitting 3F repeatedly for a very cold winter, and I have no doubt the same would happened to it even in the heart of Manhattan, unless it was planted next to a heat exchanger vent.* The urban heat island only goes so far, or Manhattan would be filled with Trachycarpus, mandarins, saluensis camellias, olives, parana pines etc. Cuz believe me, *someone* has tried to plant those at various times. (I have firsthand knowledge of at least one of those being planted in Manhattan 20 years ago. And it surely isn't there anymore!) Of course those sort of plants might even skate through mild winters - mangoes and avocadoes have gotten lucky for a season or two or three in zone 9a London. Does that mean mangoes 'grow in London'? Or course not! * which still might not permit its survival due to other adverse effects that could have, like preventing dormancy, drying the foliage out, or whatnot. Just saying cities would tend to have odd few square meters of outdoor physical space with certain scenarios that could provide warm air. As it is I think many of those air exchangers end up on rooftops. One of the only Phoenix canariensis that might be still alive in London was not only on a south wall, but I vaguely remember there possibly being some kind of air vents nearby. I saw it in 1999 and pictures had been posted of it since then. That's the sort of plant that wouldn't be bothered by dehydrating air flowing by, and in fact, in London, would probably like it!