I have some triple super phosphate i want to use around my established fruit trees to help them harden off for the winter. There aren't any application rates mentioned on the bag so i don't know how much to use. Most fertilizer app. rates are calculated by using x amount based on the diameter of the trunk measured about 2 feet above the soil line,but not sure if this also applies to triple super phosphate. I live in Southern Calif. where soils are on the alkaline side. How much can i use w/o over doing it? Thanks.
What sort of fruit trees are they? What is your winter like? When will that be? Can you explain how adding phosphate helps a fruit tree harden for winter?
I have citrus(oranges, lemon,several different mandarins, pummelos, kaffir limes, bearss lime) cherimoya, persimmons, plums, apples, jujubes. I would say i am in zone 9. We occasionally get into the 30's, (December-February) but not often. Phosphate takes about 8 weeks to work so i want to apply before the winter rains. From what i remember from my soil and fertilizer class in college, phosphorus is responsible for flower/fruit development,hastening maturity of the plant, enhancing root development,and increasing cold hardiness.
The commercial citrus growers around here don't add anything beyond urea to the soil. I spoke with a county Ag guy about fertilizer some time ago, he said that if he were asked to show a site with inadequate phosphate that he would not have any idea where to find one. Check the phone directory for the county advisor, you can get some localized information from them.
Phosphorus is one chemical that plants just take up as they need it. It is hard to use too much. However it is very wasteful to use too much and it does build up in the soil. For plants that are in good health and producing fruit, the application can be on the light side. For plants in poor health and not producing fruit, the dose should be heavier. The only way to optimize your rate is to take a soil sample and send it with the type of crop you are raising to your county agent. One of the best indicators for phosphorus is carrots. If you are deficient in phosphorus, you won't be able to grow good carrots.
You don't really need phosphorus for winter hardening.
If fruit production seems reduced, it could be that phosphorus in the root zone has been depleated. Phosphorus does not leach through the soil, so applying on the surface in anticipation of winter rain won't work. (In any case, it seems that there won't be any appreciable rain this winter.) Instead, the phosphorus must be injected into the root zone. For my fruit trees, I take a 2-foot length of steel rebar and poke holes in a circle just inside the "drip zone", the area where rain would drip from the outermost branches. Then, with a funnel, I fill the holes with super-phosphate.
Citrus requires more than merely nitrogen. They require an acidic fertilizer with iron and zinc. Most commercial citrus foods are acidic and contain iron but lack zinc. I have an old sack of zinc sulfate that I use, applying only a small amount to each tree. Frequent (twice a month) light feeding from the end of March to the beginning of September is better than only one or two heavy feedings in the spring. ]
Don't feed later than two months before the first expected frost; feeding promotes tender new growth that will be killed by frost. This is a good rule for all subtropical fruits, not just citrus.
I'm not familiar with the care for your other fruit trees. However, plums require care similar to peaches but with less pruning. My peach tree gets a spring feeding, using generic lawn food broadcast in its drip zone.
I used to live in Santa Monica, now i live in San Gabriel Valley. It's colder here. Actually i don't know if the soil is deficient in P. I thought my teacher said to apply it in winter to help harden the tress off a bit. This class was 25 years ago, so i'm sure i've forgotten some of the details.
Sounds very much like my orchard and my climate, although it gets down to -4C (23F if my sums are right) sometimes , except for being Southern hemisphere.
Phosphate takes about 8 weeks to
My concern is that if your soil isn't P deficient it won't make much difference but if it is you are encouraging growth as the season slows down. Here those new shoots would be frost targets. If you don't get frosts why attempt to harden the plants? My regime is to fertilise the fruit trees spring and summer not autumn or winter.
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