I always graft the European or late blooming and high chill prunes or plums on the top southeast, south and southwest canopies. This way, they’re never shaded out even when they’re the last ones to wake up in a multigrafted tree and grafting at the top of the canopy means they get higher chilling hours than the ones below!
The photos show my European plums or prunes in the South and Southwest portion of the canopy. They’re just starting to bud out, bloom and push leaves but are not being shaded out by the Asian plums and other early varieties! So they’re guaranteed to have a piece of the sun and be productive even if they’re the last ones to bloom or awaken.
The Euros were grafted to the Hollywood plum and the purple ornamental cherry plum (P. cerasifera). The Hollywood plum was grafted to the ornamental plum. I am surprised that the Euros really have very vigorous growth on Hollywood plum. I have grafted Euros before on Santa Rosa and other Asian plums and their growth have been lethargic, but not on Hollywood plum. Of course standard rootstocks such as Myro, and cherry plums, St. Julien are all cool with Euros and I use them as interstems when needed.
How’s that? It’s colder closer to the ground, isn’t it? I’ve heard that tall trees are more protected from late frosts- so maybe that would be of benefit.
Anyway, the advice is good- it’s very important that all grafts be exposed to good light. When I transplant trees with a grafted branch I usually point it south, unless it is a more vigorous variety than the rest of the tree. When grafting trees in the ground, I don’t always have that much choice- I’m looking for water sprouts usually.
The simplest explanation is that frosts form first at the top of the canopy, not on the branches below the top of the canopy.
detailed explanation here…
Think about night time, and it has very little to do with height, but rather if the object has a cover above it or not. Certainly the top of the canopy has no cover, the same with bare ground. Any object that has temperature above absolute zero loses heat energy via the black body radiation. The top of the trees has nothing blocking against it from losing its heat energy via black body radiation, and so is the bare ground. the stems under the top of the trees loses less heat because there’s a cover above them.
That is why frosts form readily first at the top of the trees. During clear, moonless, windless nights, frosts can form even if temperature is much above freezing point of water.
Primarily black body radiation is between surfaces, one is on earth and the other is outer space. Outer space radiates at 4 degrees Kelvin, while objects on earth is way above that temperature, at above 273 deg Kelvin. The rate of radiative energy lost is proportional to the 4th power of absolute temperature, so at night, objects on earth loses more energy to space because of higher absolute temperature. Exposed shiny objects such as glasses, mirrors, car windshields, the frost will form on them first. Clouds will reradiate back the energy, and the moon will also radiate back some energy, so usually it isn’t much colder when there’s cloud cover or moonlight. Wind is another matter, as it works via convective and sensible heat transfer. All of these are done through energy balance.
The taller portions of the trees are protected from frosts and freezes only on very particular situations. The trees should be really very tall enough AND there is an inversion layer, which means that the higher you go the warmer it gets because the inverted air is trapped. Normally, it is adiabatic lapse rate when there’s no inversion, the higher you go, the colder it gets. We have agrometeoroligical classes dealing with this and we collect agricultural weather data during my graduate studies. The California Valley will oftentimes have inversion layer because the surrounding mountains trap the air, and unfortunately trap also all the pollutants coming from the Bay Area making the air very unhealthy.
Are You are talking about frost, and not temps? I’m thinking of what gets killed first by frost on my property and low points are it. Temps are most often lower the closer you get to the ground- indoors and outside, I believe. Fans are used to prevent convection frosts by bringing warmer air towards the ground.
Am talking about both, the temperature of the plants are subjected to. Normally, the higher you go the colder it gets. It is called the normal adiabatic lapse rate. Higher elevations are colder than lower elevations.
I think you missed my explanation about the inversion layer, when it gets warmer instead of colder up to a certain height. When there is an inversion on windless nights, fans are used to mix the colder air and warmer air when the air is trapped.
Yes I know. But what you are saying is not correct, IMO. Yes higher elevations eventually leads to lower temps, but cold air settles locally. I was raised near the creek of a canyon- a little above me on my street, people could raise citrus and avocados, they were killed on my site.
I think I can see your point- you may keep your grafted scions dormant for longer because overall temps are lower further up in the tree- it is at night that temps become lower close to the ground- on still clear nights. I was focusing on frost damage that occurs mostly at night, without considering average temps throughout the season and throughout the day. That is, of course, my primary focus in trying to protect fruit and vegetables. .
In many books I’ve read in the past on choosing an orchard site a great deal of attention is put on air drainage created by locating an orchard on a slope- which helps the cold to drain downhill. Of course, water drainage is even more crucial, but it is sometimes suggested that trees and brush downhill from an orchard can restrict the exit of cold air.
I did many agromet models as laboratory exercises validated with automatic data logging of various parts of the canopy during my graduate studies at UC Davis. I did many energy balance measurements including light attenuation and temperature differences throughout the canopy profile. We even did rice models and we built one of the most accurate phenological models that made its way into California Expert Systems software.
I contradict a lot of statements submitted on this forum, but get the most pleasure when my statements are contradicted and I learn something new- not that my first reaction to being proven wrong is always positive, of course. But a slight surge of humiliation always helps a lesson to stick, and I need all the help I can get. .