I've just started posting here, but I've been gardening strictly organically for 34 years. And IMO pH meters and soil tests are a complete waste of money. Why? Because no matter what they reveal, the solution is always the same: add more organic matter to the soil. The original poster wrote "From what I've read, the problem could be deficient N, excess N, deficient P, deficient K, deficient Ca, deficient Fe, pH, watering problems, or fungus." If tomatoes get too much N, it inteferes with the uptake of phosphorous, which is crucial to fruit set. You can actually reduce your tomato yields by using the wrong commercial fertilizer. And the amount of calcium in soil is virtually never a problem, like with BER. It's not enough calcium reaching the fruit that causes it. Being a Simple Person, I just use grass clippings for fertilizer. They will supply all the nutrients your plants need, in the right form, the righ "balance," and the right amounts at the right times. It's the way nature has been feding plants for millions of years. Having been to San Francisco many times, I know grass clippings might not be the easiest thing to get in some areas. But given their incredible value, I'd make some effort to find some- like in parks, around hospitals, or commercial buildings. If the groundkeepers aren't using mulch mowers, they'll probably be happy to let you have some?

I've wondered about this question too. With ordinary plants in potting soil, the risk of over-fertilizing is that as the water in the soil is taken up by the plant or evaporates, the concentration of fertilizer salts can increase greatly. At some point the osmotic pressure of the water and fertilizer surrounding the roots can interfere with water uptake by the roots and possibly damage the roots. With mounted orchids though, I haven't seen any information on what happens physiologically when watering with fertilizer. It seems three things are going on: (1) the roots are absorbing water into the velamen, (2) the roots are absorbing fertilizer ions, and (3) water is evaporating into the surrounding air. I would assume that you would want all of the fertilizer to be absorbed before all of the water on the surface of the roots is gone. Otherwise there would be a thin, dry coating of all the residual fertilizer on the roots. So the question is how fast roots can absorb fertilizer - anyone know? It would seem that for that reason, it would be bad to use any fertilizer at all when the air is warm and dry, since the water on the roots would evaporate too fast.

Hi Satcat, My quick answer to your salimeter question is that I doubt that you will be able to read the concentration of a hydroponic nutrient solution with it, because the nutrient solution would be far too weak to give a reading. Many years ago I gave up using a conductivity meter because I could not correlate its readings with what I knew was in the nutrient solution. So I ditched the conductivity meter. However, I would advise you to get a good pH meter and know how to calibrate it properly. I explain all of this on my Australian web site below. If you save each page of my web site, as its own name, on to your computer, all in the one directory, then you will be able to navigate from page to page with ease when you are off-line. Go to the page "Hints for Success" and read Tips number 4, 5 and 6. Tip # 9 is also worth reading. See also my "FAQ" page and see what it says about "osmosis" and making your nutrients too strong. If you have any queries, just use the email address on the web site. Cheers, Jimr007 Australia. Here is a link that might be useful: Simple Sand Hydroponics

For pH, i use a pH test kit, with drops of pH sensitive dye. Cost about $10, more then accurate enough for what I need, and I don't have to worry about replacing pen tips. I set up my pH at the beginning, and put in an air bubbler to agitate, mix the pH Down in, and also clean out some of the chlorine thats in the water. Then put it in my system and forget about it. I've checked it after two weeks. It crept up a bit, but was still acceptable (just below 7). So now I don't worry about it.