What's the best N-P-K ratio for Norfolk Island Pine?

Question

What's the best N-P-K ratio for fertilizing Norfolk Island Pine? According to this article I should go with 10-10-10.

Is it a good combination? Also, how should I apply it? Should I spray it on, or give it with water?

Update:

I live in Jaipur, India. Current temperature ranging between 15-25 degree centigrade. Soil is mixture of 30% vermiculture and 70% sand. I didn't get it tested because I don't have a soil testing center nearby.

I bought this plant around 6 months ago, but there are no new leaves.

Answer 1

Because the soil you are using is mostly sand, I would recommend using more nitrogen than I otherwise would. I am assuming (because you know the ingredient ratio of the growing media) that it's in a pot. Use something like a 12-8-8 fertilizer every two weeks while the tree is growing. Do not fertilize during dormant periods. Norfolk Island Pines aren't too picky fertilizer-wise, and many people use 10-10-10 with okay results.

Do not spray it on the foliage, because these trees do not take it in very efficiently, and fertilizer residue could build up, slowing photosynthesis, eventually killing the tree.

Use it as a root drench every 2 weeks when you water. This will be the most efficient way to apply it, and also spread the fertilizer evenly through the root system, so you don't burn the feeder roots.

Answer 2

Do you have this plant in a container or in the ground? If in the ground I'd be more concerned with maintaining a pH range that satisfies this plant's needs and I'd fertilize organically by topdressing with compost or watering with compost tea regularly. I believe but might be mistaken that this plant prefers soil slightly more acidic than the average plant.

Knowing what nutrition the plant needs is based on what your soil lacks and what is there but unavailable to the plant. For this reason this question is tough to answer without a soil test. You usually can do soil tests by mail, and a university might help you with that. Even give you recommendations as to what the plant will need.

You can test the pH of the soil with very cheap do it yourself test kits. I'd start there and with compost and then look for signs of nutrient deficiency.