Yes they work and no they don't. Most of the time they will provide a reasonably accurate pH reading for awhile, but they can't be calibrated so once they don't read accurately any longer there is no way to correct it.

They also do not work at measuring moisture levels. What they actually measure is electrical conductivity which the meter translates to moisture levels. Put the probe in distilled water and it will read dry.

The combined NPK levels are useless. Again, it isn't actually measuring them.

About the only thing the meters are good at is measuring pH, but for a little more money you could get a digital unit complete with calibration solutions that would be much more versatile.

I'm giving you a link to Dan Trimmer's lecture on daylilies. He's a professional grower, and mentions meters specifically. I've read somewhere else that only the pH measure is accurate on these meters, and people recommended one just like you show except measuring only pH and 'fertility'. Only use it for pH.

Here is a link that might be useful: pretty accurate

You wrote " I put so much effort into it and the yield has been extremely low."

What did you do -- specifically -- prior to planting? If you only dug, then planted, that was the problem.

Please give us some details.

For jean001, I actually had 5 different types of soil I used this year.
Soil # 1 my natural soil (decomposed granite) which was dug and sifted to 3.5 feet and had peat moss mixed in with the dirt about 1:3 ratio. This bed yielded tall tomato plants which dropped most of their blossoms. The set very few fruits toward the end of the season. I was able to grow 1 set of radishes in this bed and no other seeds would even come up in it. The peppers in this bed were small and thin walled. I did use a small feeding of miriclae grow organic veggie fertilizer
Soil # 2
Again dug to 3.5 feet and sifted, added 1/3 peat moss and 1/3 mulchy compost which is like one stage away from being fully decomposed, and 1/3 natural soil. This bed stunted all seedlings I planted in it. As the summer passed it was able to support 3 sunflowers and several acorn squash vines that each gave one sickly squash.
Soil # 3
Straight mulch which I had aged and left covered and moist for about 6 weeks prior to planting. I have many large & healthy looking tomato & pepper plants currently in this bed. They have set a decent amount of fruit but are now dropping most of their blossoms. I have added in some gypsum and fertilized each plant with blood and bone meal. (this bed is my hope!)
Soil # 4
Mulch, peat moss, and vermiculite. Again plants were stunted. Seed failed to sprout. Bed produced a few green onions, one kale plant, and bush beans did okay in this bed.
Soil #5
Alternated sifted decoposed granite and aged mulch which could be called compost. Plants did just okay.
I have a lot of spider mites right now too. I am very discouraged. I think I planted over 50 tomato plants which most came to full adulthood and my yield was not even enough to share with neighbors. Any advice for me? Thank you so much!!!

Aww, Spanky, I don't have any advice, but I just wanted to drop in to tell you that I know how you feel. It stinks to put in so much effort, and harbor so much hope that you're going to have so many veggies that you won't even be able to give them away anymore, only to have a disappointing harvest. You have my sympathies.

It's my first year, and all of my tomatoes became infested with psyllids, a rarity here in these parts (lucky me!). That was my biggest disappointment. The zucchini and squash that everyone said would be coming out of my ears really just... didn't. My jalapenos have done ok, as has my one Thai chili plant. Potatoes never sprouted. Cabbage moths got one of my collards, but the other is doing well. Overall, it's been a bit disappointing, but this whole thing is a learning process, so I'm confident that sooner, rather than later, you'll get it at least partially figured out, and so will I! And I only say "partially" because I'm not sure that anyone is ever finished learning when it comes to gardening, much less life!

Mulches and peat moss are high carbon sources that when mixed in soil will cause any soil bacteria there to spend all their available energy digesting that and not feeding your plants and that will cause plants that do grow to be stunted and chlorotic.
Start now to work on that soil so it can grow plants next year by contacting your state universities USDA Cooperative Extension Service about having a good, reliable soil test done. Forget the meter. While waiting for the report about the soil test above use these simple soil tests,
1) Structure. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. A good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drains too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer you soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.
to see what your soil is now and what you need to do to make it better, such as adding more finished compost.

So the bed doing the best is the only one that was fertilized at all (with blood meal)?

If that is correct then the solution to the issue is straightforward, fertilize all beds.

Peat moss is fine for amending a soil, but it contributes nothing in terms of nutrients.

Vermiculite also contributes nothing in terms of nutrients.

Mulch will be low in nutrients and depending on what it is made of, may tie up nitrogen until it's composted.

Compost is fine, but may not be enough depending on what it was made from, how much was used etc.

I would say it sounds like you did a good job amending your soil in terms of making it a nice place for roots to grow, but neglected to provide adequate nutrition for the plants.

At least that is what I take away from your descriptions.

Getting a soil to the point where it can grow healthy plants with no fertilizer inputs other than compost isn't an overnight thing. It may take one year with a nutrient retentive soil or several-many years with a soil that doesn't retain nutrients well. Until it gets there fertilizers are needed or plant growth will be poor.

I agree with Justaguy. You need organic fertilizers--blood meal, bone meal, greensand, Starbucks coffee grounds, shredded fall leaves, grass clippings. Work it in now, this fall, and let it pump up your soil life over winter. Layer on all the grass clippings and leaves you can get your hands on, like a sheet composting site.

All the peat moss is pretty inert from a nutrient standpoint, but don't think of it a loss. It will be holding moisture for you and opening up the texture for oxygen movement as well.

It takes time to create a fertile garden soil. Even with fair soil, compost, and organic fertilizers, my new beds never measure up to the two year old beds. The bacteria, fungi, and earthworms take a year to establish soil structure, and two years is even better.

Then, watch out. Don't be planting fifty tomato plants unless you and all your neighbors also put up cans and make paste.

Do you have any sort of recipe Petalpatsy? Like 20 lbs bone meal, 10 lb coffee grounds per some many square feet? I have been gardening for a long time, but have not yet figured this detailed chemistry portion of getting it right! Thank you All so much!

No, I don't really have a recipe. Ideally you would have a soil test done to guide you, but failing that could just follow the directions on a bag of bone meal (4-12-0), greensand (0-0-3) and put down coffee grounds 1/2 inch thick if you can hit your Starbucks often enough to get that much. Work that into the top few inches and cover with as many grass clippings and leaves at you can. Blood meal is completely soluble in water, so if you choose to use it for a fast boost of nitrogen you must do that in spring or it will just leach away over the winter.

I know the Atlanta Botanical Gardens has a recipe and plan for their Rose Garden that is organic--a lady gave me a copy when I visited there, but I don't recall the specifics. If you go to their website they offer a plant hotline and promise a master gardener will email you back an answer. Since they already have this plan printed up on fliers, they can probably email or snail mail you a copy without too much hassle.

Here is a link that might be useful: Atlanta Botanical Garden Plant Hotline

Yes soil testers actually work. There are two different types of testers, electronic and soil tester. The electronic is a bit more expensive but is faster and less expensive. The link has a wide variety to choose from.

Here is a link that might be useful: Soil Testers