two trees and three fruits
All varieties of apple trees should be cross-pollinated with another apple or crabapple variety. Although some apple varieties, such as Lodi, Liberty, Empire, Winesap, Jonathan, Jonagold, Gala, Golden Delicious, Rome and Granny Smith may be listed as self-fruitful, they will set more fruit on an annual basis if they are cross-pollinated.
yes
hand pollination will increase yield. By definition, however, grapefruit trees are self-pollinating.
Avocado trees are very susceptible to root rot. Therefor, they need soil that drains thoroughly and well. However, they also need rich soil. So a loamy, sandy soil is good for avocado trees that are outdoors, and a loose, rich humus soil is good for potted avocado trees.
yes
No, they are self fertile.
Na daaah of caorse you do
you need to say what tree you are asking about.
The first thing is to ensure you have a compatible pollinator. It needs to be a variety which overlaps the blossoming time of your tree - Jonathon is a useful pollinator but a specialist fruit nursery can advise of what you need especially if you can tell them when your tree flowers or can take them a fruit sample. Also, anything that attracts bees will be helpful.
No, apple trees do not need a companion tree. An apple tree will flourish all by itself. Most varieties of apple require a pollinator in the vicinity. Only a small number are self fertile.
In a word, NO. Some avocados do better in the tropics,eg, in Australia, the Shepard thrives in the tropics, and some like a mild climate,eg, Hass & Wurtz. Brendan, Australia.