I have many young trees that have a lot of yellow leaves. I read this can green them up. Has anyone tried this and if so how ?

Compost tea.
Five gallon bucket filled 1/4 the way up with worm castings or manure etc. 1/4 cup molasses fill the rest with water. Stir with a drill with a paddle or somthing else.
Put in covered area stir every other day gently . For best results use a cheap aquarium pump and a bubbler stick let it stand for 10 days gently stir every other day. leave air bubbler on for the whole 10 days.

Hi brianm,
If your trees have deficiencies, it may help.
If your trees suffered either from over watering, under watering, heat , being root bound, being in a smallish pot, it will help but won't solve the problem .

For the manure tea, I fill 1/4 to 1/2 of a 200 liters (50 gallons) barrel with manure (and dried weeds like mint ...) and add water up to the top.
Let that alone for 5 days or more, and dilute half of less of that tea in a water can - refill the barrel afterwards. Do your own tests as I don't know if your trees are potted.
What I often do, I water a first watering-can with tea, and later a watering-can of water. I try to avoid too much run-offs .
Hope your trees are a bit away from the house :) .

Are your trees in ground ?

A general fertilizer would help too and would be less smelly - especially the barrel is a good lady repellent .

I certainly would recommend compost tea, but first I would try to identify the cause and nature of the deficiency and correct that.  The compost tea does not add much in terms of nutrients to the soil.  It does increase the biological activity that helps break down the organic matter making the nutrients available to the plants.  However, if, for example, your PH was too high/low, or if you had some root diseases, it could prevent the plant from being able to uptake nutrients that are already present.  It may be something like a nitrogen or iron deficiency that can easily be corrected by amending the soil.  I would still use the compost tea, just realize the compost tea does not add nutrients to the soil, it just helps break them down to a form where they're usable by the plants.

iron deficient?

Not manure tea, but alfalfa tea and other suggestions

http://figs4funforum.websitetoolbox.com/post/how-good-was-your-fertilizer-program-6522666?highlight=alfalfa&pid=1279507470#post1279507470

Here are some pictures of what I'm talking about. The soil is a mix of soil and small bark. I've used this fast draining mix for a few years with good results. The pictures are definitely greener then what they are.

This year I have been traveling too much to make manure tea. But last year I used it a lot. I simply added a sm bucket full of manure to one of my rain barrels. Stir it every few days. Add more manure when it stops looking the color of  "tea." My plants really loved it last year and I am sad that I have not been home enough to do it this year. But my wife is kind of grossed out by the tea so I can't ask her to water my plants with it when I am gone.

Brian,

A plain Miracle Gro or a Dyna-Gro Grow or Foliage-Pro would help for sure. I wouldn’t go too far to fix this, it looks just a nutrient deficiency, a complete fertilizer will do a trick.

Hi Brianm,
Time to pot up, in my opinion.
I would pot up to 1 gallon pots.
IMO, those need space to expand their roots.