Most of us will pamper newly planted trees for their first year, if at all. After that, trees are usually left to their own devices. I have to say, there is very little agreement out there about whether trees need any supplemental feeding and a whole lot of qualifications, even when fertilizing is recommended.
Where Most Experts Do Agree
If you are fertilizing the lawn around a tree or a garden surrounding a tree, the tree should be fine. Trees are water hogs and they will take up whatever nutrients you throw down.
If you are going to feed them, do it in late fall or early spring. Late fall seems to be the preferred time, so that the roots can take in some nutrients to get it through the winter and when the ground thaws and the tree wakes up in the spring, food is already in the soil waiting for it to start feeding.
Feeding during the growing season can promote a lot of tender growth that is ripe for problems.
A soil test is the best way to know if your soil is providing enough food for your tree. However you can also get a good idea of how healthy your tree is by checking its growth and color.
If you’re getting new shoot growth of at least 6 inches, your tree is probably fine. If it is less than 2 inches, feed the poor thing.
Then look at the leaves. Are they green (or whatever color they should be)? Are they bright and healthy looking? Again, probably fine. But if you see streaking, dark veins or yellowing, the tree may need food or it may need a pesticide. Either way, it is stressed and you should do some more investigating.
Most of us have enough garden chores already and we’re not going to start feeding the trees. Just make sure you keep an eye on them and notice any changes that could signal trouble. It’s a lot easier to help a tree that has just started struggling than to heal a tree in decline. And a bag of food is a lot cheaper than having a tree taken down. Hugely cheaper.
One last thought
Don’t be so tidy about raking up every last leaf. Leave them be in the fall, unless they are going to smother other plants. They will break down during the winter and you can easily mow the in the spring, turning them into lovely, free tree food.