lemon tree woes
my meyer lemon is in a very large pot, just repotted last year. it sits on the front porch facing west and is protected by a small greenhouse with a heat lamp when really cold. it gets scale on it, but about twice a year I work it over with a neem oil concoction. we had a large crop of lemons last season but a lot of very yellow leaves. once the lemons were gone, I pruned the plant and removed the yellow leaves and fertilized it with citrus fertilizer. the new leaves exploded out nice and dark green. a lot of the new growth has thorns on it (this is a new thing, never had spikes before) and the leaves are beginning to yellow up. there is only one small branch that has any indication of blossoms. here's a picture of the leaves. what can I do to bring my lemon tree back to life? and is there something else to do about the scale? thanks
Citrus trees usually have a couple of nutrient issues to stay on top of. The one that can cause chlorosis or yellowing of the leaves is a micronutrient issue. The soil pH can get a little too high and not allow iron and zinc to be available. You should use a little acidifying fertilizer like sulfate of ammonia and add a micronutrient mix that includes iron especially. You can use a foliar spray with micronutrients too to help the chlorosis.
To go after the scale you can use either a horticultural oil spray as long as the temperature where your tree is not over 85 degrees. You can use Safers soap spray to get scale too, although I think the oil works a little better.
If you have a simple pH meter that you stick in the soil to get a reading, that can help you know how much you need to acidify your soil. You can spray or fertilize a lot without any success to solve the leaf yellowing if the soil pH stays too high.