Question
It's getting hot now in Arizona (Casa Grande - between Phoenix and Tucson) and our spring planted citrus trees (orange, lemon, lime) are starting to exhibit more than a few yellow leaves.  We are trying to give them more water - every morning - and the leaves have looked better for a while, but now it's back to yellow.  I looked at a university hort site that had pictures of different yellowing deficiencies - and our leaves looked like the nitrogen deficiency photos - just yellow all over - older leaves first - no mite webbing or that sort of thing - no spotting.  Would a 20-10-10 fertilizer help perk them up?  We've been using Miracle Grow every once in a while, but that doesn't seem to be helping much.  We've also been putting our used tea leaves on the plants - is that contributing to the nitrogen loss with a mulch break down effect?  Is there a better brand fertilizer for citrus?  Also, had brown spots on apple leaves - I believe due to aphids - and we got an aphid treatment - gravel like pelts to put on ground - and the tree is looking better, but still more of that white coating on back of leaves.  It says to wait 4 weeks between treatments, but in the meantime, more leaves are turning brown rust like at edges and drying up.  Is there any fertilizer that will help the tree to reverse some of this damage?  Thanks.  

Answer
Fertilize your trees on a regular schedule - not only in response to nutrient defieciencies. Fertilize every 3 months (3-4 applications per year).

The right type of fertilizer would be 20-10-10 e.g. a 2-1-1 ratio or 3-1-1 ratio. Such as 29-14-14, 20-10-10, 10-4-6, etc.

The best type of fertilizers to use is those that acidify the soil. E.g. Miracid Soil Acidifier is a water soluble product that works well and has the right ratio.

Yellowing leaves indicate lack of fertilizer or poor drainage. If the leaves remain yellow despite fertilization it could be poor drinage and consistently damp soils. Is your soil heavy clay ? How well does it drain ?? If this is the case, the tree may never grow properly and the best way to rectify would be to lift the trees out of the ground, amend the soil in a very wide diameter atleast 50% deeper than the root ball and then re-plant the trees (keep top of rootball a few inches above soil level to allow for settling).


Dark green, lush leaves with burned tips indicate excessive fertilizing. Marginal burn is often due to too much fertilizer, so if you have just fertilized with miracle grow, it would not use any more fertilizer for now.


Have you had a soil test done ? Citrus trees prefer a pH of 5.5 to 6.5. If your soil test states that soil pH is above 6.5 you will need to apply sufficient amounts of acidifying fertilizers and/or acidifying elements (such as elemental sulphur) to lower soil pH. This can be tricky, but before adding anything, do have a soil test done.

From the sound of it, your citrus has had it's share of problems (aphids, fertilizer frequently, etc) and it is probably very stressed which can be main cause for loosing leaves, too.

A few things to check now:
- soil pH
- drainage
- and while you have soil test done: fertility of soil
- if you end up lifting and amending soil, mix good quantities of peatmoss sphagnum (acidic) into the planting hole together with a bulking agent (fine wood chips) and mix with 50% native soil.

always fertilize regularily at fixed intervals and not continously in response to problems, especially when plants are stressed.

Sorry to hear about your trees.