Question
we live in Hillsboro, Oregon and would like to know just what kind of organic fertilizer we can use on an orange tree we bought and planted.  Its an Washington Navel Orange that we bought from Lowe's.  Please help us find the right organic fertilizer to use.

Answer
Taiwan's Food and Fertilizer Technology Center posts a cheat sheet on this very subject, 'Fertilizer Management for Citrus Orchards':

www.agnet.org/library/bc/52006

And they spell it out clearly in plain English: 'The Law of the Minimum Nutrient means that in Citrus trees, as in other crops, the growth of the plant is limited by the nutrient element present in the smallest quantity, even if all other nutrients are present in adequate amounts.  It is of the utmost importance in Citrus production to know which, if any, nutrient element is the limiting factor.  If there is a deficiency of any nutrient, then the fertilizer program must remedy this.'

They make one other point that is important in your case:

' The availability of nutrients in the Soil which can be taken up by the trees is strongly influenced by the Soil pH.  Tree growth and fruit yield are also influenced by the Soil organic matter content, and the levels of various nutrients such as Phosphorus, Potassium, Calcium and Magnesium.'

You don't have to follow all their chemical-shopping list advice.  But you really shouold order a Soil test to find out what, if anything (and there's always something), is NOT in your Oregon Soil, as well as that key to nutrient availability, pH.

Since you are planting this Tree in the ground, it is vital that you promote the growth of Mycorrhizal Fungi underground to optimize uptake of moisture and nutrients.  These are THE best Organic Fertilizers money can buy.  Remember that this plant probably hails from a heavily managed, high chemicalled location and may even be reacting to its new home as we speak.  There may be plenty of damage that was done while it was in seclusion in the nursery.  EZ does it.

Also consider that when it comes to Oranges and plant nutrients, less is more.

That statements is based on a study done by University of Florida, Institute of Food and Agricultural Sciences and reported in 2002, 'Effects of Water and Nutrients on the Postharvest Quality and Shelf Life of Citrus.'  They pointed out, 'Although fruit quality usually improves as soil moisture and nutrients increase from deficient to optimum, levels that produce maximum yield may not always correspond to those that result in the highest fruit quality and maximum quality retention.'

Too much Nitrogen is not a good idea, they noted.

'High N levels in young trees can promote coarser fruit with thicker peel, while high N in mature trees can result in more and smaller fruit with thinner peel.'

Here's the URL:

edis.ifas.ufl.edu/CH158

Any questions?  Need to know where to get your Soil tested?