Why does my garden's soil always seem to be lacking essential nutrients despite regular fertilization, and how can I test for these deficiencies?

I totally get your frustration, it's like your garden is just not responding to the fertilizer. I think it's great that you're looking into the soil itself now, because that's often the root of the problem (no pun intended!). Have you considered getting a soil test done? You can buy a DIY soil testing kit online or at a local nursery, which usually includes pH test strips and nutrient testing solutions. This will give you a good idea of what's going on in your soil.

I'd recommend looking for deficiencies in nitrogen, phosphorus, potassium, but also calcium, magnesium, and sulfur. These are all important macronutrients that plants need to thrive. Nitrogen is great for leaf growth, phosphorus for root development, and potassium for overall plant health. Calcium and magnesium are crucial for cell wall development, while sulfur helps with plant resistance to disease. If you find any deficiencies, you can try adding natural amendments like compost, manure, or green sand to correct them.

As for testing, I've heard great things about the pH meter from Luster Leaf. It's pretty accurate and easy to use. Just insert the probe into the soil and read the pH level. For nutrient testing, I like to use the Rapid Test Kit from E.B. Stone Organics. It's a bit more expensive, but it gives you a good idea of your soil's nutrient levels. Plus, it's easy to use and doesn't require any special equipment.

I hope this helps! Good luck with your garden, and don't hesitate to reach out if you have any more questions. Happy gardening!