I still have so much to learn...
Sorry for the loaded question Paul. I know that fertilizer choice is probably a volatile subject with any number of good ones out there so I will have a look around and see for myself. Currently I tend to use a Seasol/Powerfeed combination, but the Powerfeed is a bit high in Nitrogen for use in early Spring, and could be the reason for some of my probs???
I know a lot of N is a problem for a lot of cold climate deciduous trees (after much research and experimentation), but I'm not so sure about celtis as I have never grown them, though I understand they deciduous.
The elements most needed in spring are potassium, magnesium and calcium. This is because trees are good at storing N and P over winter. K is responsible for cellular osmotic pressure (extremely important for cellular health) and many other plant health functions, magnesium for chlorophyll development in new leaves, and calcium for proper cellular division at shoot tips and cell wall strength. None of these will actually make a tree grow, just keep it healthy (but will continue to grow well because they are making more efficient use of N& P). It is the P and N that makes plants grow.
It is easy to make a batch of K, Mg, 1/4 teaspoon on potassium sulphate (sulphate of potash, make sure it is powdered, not lumpy) and 1/2 teaspoon of magnesium sulphate (Epsom salts) to 9 litres of water, you can use this every second or third watering. For calcium, sprinkle some fine gypsum over the top of the plant. All of these chemicals are available from Bunnings, and provide much useful sulphur as well.
Then every two weeks, or when you think the plants need it, hit them with your Powerfeed. This will control vegetative growth.
Paul
Last edited by 63pmp on September 20th, 2013, 9:14 am, edited 1 time in total.
So I thought about what are the exact amounts of Mg and K in the recommended amounts I gave, and I even went to the local hardware and looked at Powerfeed. So looking at the ppm of 1/4 level teaspoon of K sulphate and 1/2 teaspoon of epsom salts we get K = 83ppm, and Mg = 38ppm. Which is fine for watering every second or third irrigation. Also as temperatures rise it would be safe to reduce the concentration of the solution, depending on how great the plant transpiration is.
I myself use a weaker solution of 42ppm K and 16 ppm Mg, I water with this every time to combat some sodium in my water.
With frequent applications of solutions people are often concerned of salts accumulating and killing the tree. This only happens if you don't have sufficient excess of fertilizer when you irrigate. So for example a 100mm pot may hold 70 ml of water, if you only supply 70 ml, or less, then salts will accumulate in the soil. If you add 90 ml, 20 ml will leach out the bottom of the pots, taking away some of the previous unused salts. Separating watering with fertilizing allows you to flush any excess that may occur. But it's good practice to really flush potting mixes every week anyway.
If concerned I would consider using 1/8 teaspoon of K sulphate and leave the epsom salts at 1/2 teaspoon ( /9l water). And observe what happens to your plants. Any changes will be with the new growth.
Powerfeed seems like a good product. I would use at 1/2 strength every two weeks to begin with. It will take 4-6 weeks for the plants to show a response, if growth is not as strong as you would like, increase rate of application to once every week at 1/2 strength.
The idea is to get healthy plants without long internodes. If you are getting long nodes the you are overfeeding with N. The problem with one shot ferts like Powerfeed is that while plants are great at taking up N and P, the plant starves of K, Mg and Ca while waiting for the next feed. Some research has shown that plants can only store enough K to last 2-3 days before becoming deficient. Frequent low dose K, Mg is similar to how plants feed in the ground, there is a constant low concentration of K and other salts surrounding the roots.
Don't be surprised if it takes a year or so to get a handle of how to fertilize, plants are slow to respond.
You should always test any new technique on a few plants before adopting anything for all your plants
A good amount to digest Paul, but will endeavor to transfer this info into my watering regime, and do my best to record the results.
Thanks once again Paul for your time.
I still have so much to learn... 
