I moved into my house about 1 1/2 yrs ago and in the front yard there is an immature crabapple. When I moved in it had what looked like cotton wool on its branches and since then has disappeared, leaving only a small amount behind. I have never pruned it, as I have only just found the label at the base of the tree! Does it need another tree to produce fruit? It's never flowered but it does get a lot of leaves.
Do you know what variety of crab apple you have? Crab apple trees are self-fertile, meaning you do not need to plant two crab apple trees in order for pollination to occur - you just need some bees. Some varieties, however, are sterile and produce no fruit. Do you know how old the tree is? It can take about five to six years for these trees to grow up enough to produce flowers.
The cottony wool like substance on the branches of your crab apple was the handi-work of a woolly aphid. You may want to inspect the tree closely for it. They can stunt the growth of the trees if they infest the tree's roots. More information on this pest can be found here:
https://www.gardeningknowhow.com/plant-problems/pests/insects/woolly-aphid-control.htm
For more information on growing crab apple trees, please visit the following link:
https://www.gardeningknowhow.com/ornamental/trees/crabapple/flowering-crabapple-trees.htm
My parents used to have a crabapple tree in the backyard (many years ago - 70's) with white flowers in spring. It had small green fruit in the summer (1/4" to 3/8"). Here's the kicker. In the fall, the fruit turned red and soft without a frost. Birds went nuts over them because it was the only soft berry tree in the fall. Our cars were covered in purple bird crap every fall, but it was good to see the birds fill up before their migration. What kind of crabapple was it? Is it some odd cross between a crabapple and chokecherry? The tree was taken down 10 years ago.
Here is a link that provides many varieties and their characteristics.
You will want to find a variety hardy to your growing zone and conditions.
A little research will yield you a tree that will be enjoyed by you and the birds.
https://extension.colostate.edu/pubs/garden/07424.html
https://www.gardeningknowhow.com/ornamental/trees/crabapple/flowering-crabapple-trees.htm
Some years my tree is covered with beautiful dark pink blossoms, and other years no blossoms. What is the difference?
There can be several reasons your seeing more or less blossoms.
First, your tree may be a alternate-flowering cultivator. The tree normally produces many blossoms one year and less the next year.
Drought can cause the tree to stop flower production to help the tree regain it's energy.
Disease can weaken a tree so that it can't support flower production.
Proper pruning.
Here is an article with more information.
https://www.gardeningknowhow.com/ornamental/trees/crabapple/flowering-crabapple-trees.htm
We have just removed a 10 yr old miniature crab tree (including the root ball) after the diagnosis of fire blight. The question is: Is it safe to replant another tree of our choice in the same spot? If the answer to that is yes, do we have to treat the soil in a particular way first?
This article should help: https://www.gardeningknowhow.com/plant-problems/environmental/planting-in-old-spaces.htm
Can I use a flowering crabapple to pollinate an apple tree?
Yes, here is a link that will help.
https://www.gardeningknowhow.com/edible/fruits/apples/apple-tree-pollination.htm
I have a Crabapple tree and a Weeping Cherry tree. I want to know what to put on them or feed them to deter the Japanese beetles. I've heard there is something you can feed the trees through the roots and it will stop the Japanese beetles from attacking them.
There are a few things you can do. One of which is to treat your lawn for grubs. The grubs often found in the lawn are the grubs of Japanese beetles and this will help reduce their population before it starts. This article will help: https://www.gardeningknowhow.com/plant-problems/pests/lawn-grubs-how-to-get-rid-of-grub-worms.htm
The mixture you asked about will help some as well. This article has some other suggestions: https://www.gardeningknowhow.com/plant-problems/pests/japanese-beetles.htm
You may also want to plant things that Japanese Beetles do not like. This article will help with that:
https://www.gardeningknowhow.com/plant-problems/pests/japanese-beetle-resistant-plants.htm
I have a young flowering crab tree and my gardener has lacerated the bark near the ground right around the tree. Should I try to repair it? If yes, how?
Clean up any ragged edges and allow the air to circulate. Do not wrap the wound or apply any wound dressing.
Watch for any signs of insects or disease in the open wound. It should began to heal naturally.
Here is a link.
https://www.gardeningknowhow.com/ornamental/trees/tgen/wound-dressing-on-trees.htm