pH needs of plants in soil or hydroponics
Jan 6, 2010 hydroponics, pH, water
With the exception of some of my acid loving plants and flowers I normally do not have to worry much about the pH of my soil. This is because I have amended my gardens with nutrient rich soils in raised beds over my alkaline clay I get naturally in my area. This and the fact that due to natural and manmade causes the rainfall is slightly acidic and given the average range for the sweet spot of most edible vegetables (see table below) is 5.8 to 6.0 having your soil slightly acidic this is perfect.
Now when it comes to hydroponics this is entirely different. My tap water has a pH of around 7.5 and the fluctuation of plant using nutrients and transpiration can cause great havoc on the pH on your hydroponic system. Now this creates a challenge but also an opportunity to have control with great precision your pH and keep your plants growing in the sweet spot for the healthiest plants and the greatest yields.
So whether you are growing hydroponically, or simply trying to figure out why your Fennel didn’t do so well last year take a look at the table below, hopefully for some hints of what happened.
Recommended pH Ranges of Vegetables/Herbs
| Plant | Low | High | Plant | Low | High | |
| Artichoke | 6.5 | 7.5 | Millet | 6.0 | 6.5 | |
| Asparagus | 6.0 | 8.0 | Mint | 7.0 | 8.0 | |
| Average | 6.3 | 7.8 | Mushroom | 6.5 | 7.5 | |
| Basil | 5.5 | 6.5 | Mustard | 6.0 | 7.5 | |
| Bean | 6.0 | 7.5 | Okra | 5.5 | 6.0 | |
| Beanroot | 6.0 | 7.5 | Olive | 5.5 | 6.5 | |
| Beet | 6.0 | 6.8 | Onion | 5.5 | 6.5 | |
| Broccoli | 6.0 | 6.8 | Paprika | 7.0 | 8.5 | |
| Brussel Sprouts | 6.0 | 6.8 | Parsley | 5.0 | 7.0 | |
| Cabbage | 6.0 | 6.8 | Parsnip | 6.0 | 6.8 | |
| Calabrese | 6.5 | 7.5 | Pea | 5.8 | 7.0 | |
| Carrot | 6.0 | 6.8 | Peanut | 5.0 | 6.5 | |
| Cauliflower | 6.0 | 6.8 | Pepper | 5.5 | 6.0 | |
| Celery | 6.0 | 6.5 | Peppermint | 6.0 | 7.5 | |
| Chicory | 5.0 | 6.5 | Pistacio | 5.0 | 6.0 | |
| Chinese Cabbage | 6.0 | 7.5 | Potato | 4.5 | 6.5 | |
| Chives | 6.0 | 7.0 | Potato, Sweet | 4.5 | 6.0 | |
| Corn Salad | 6.0 | 6.5 | Pumpkin | 6.0 | 6.8 | |
| Corn, Sweet | 5.8 | 6.8 | Radish | 6.0 | 6.8 | |
| Courgettes | 5.5 | 7.0 | Rice | 5.0 | 6.5 | |
| Cress | 6.0 | 7.0 | Rosemary | 5.0 | 6.0 | |
| Cucumber | 6.0 | 6.8 | Rutabaga | 6.0 | 6.8 | |
| Eggplant | 5.5 | 6.0 | Sage | 5.5 | 6.5 | |
| Fennel | 5.0 | 6.0 | Shallot | 5.5 | 7.0 | |
| Garlic | 5.5 | 7.5 | Sorghum | 5.5 | 7.5 | |
| Ginger | 6.0 | 8.0 | Soybean | 5.5 | 6.5 | |
| Horseradish | 6.0 | 7.0 | Spearmint | 5.5 | 7.5 | |
| Kale | 6.0 | 7.5 | Spinach | 6.0 | 6.5 | |
| Kohlrabi | 6.0 | 6.8 | Squash | 6.0 | 6.8 | |
| Leek | 6.0 | 8.0 | Swede | 5.5 | 7.0 | |
| Lentil | 5.5 | 7.0 | Swiss Chard | 6.0 | 6.5 | |
| Lettuce | 6.0 | 6.5 | Thyme | 5.5 | 7.0 | |
| Marjoram | 6.0 | 7.5 | Tomato | 6.0 | 6.5 | |
| Marrow | 6.0 | 7.5 | Turnip | 6.0 | 6.8 | |
| Melon | 6.0 | 6.8 | Upland Cress | 6.0 | 6.5 |
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January 6th, 2010 at 4:19 PM
My water pH is high as well, but I never adjust it. I set a 5-gallon bucket of water out overnight and allow the clorine to gas off. General Hydroponic’s nutrients are pH adjusted, so it is about 6.0-6.5 when mixed.
The pH drift allows macro and micro nutrients to be absorbed at different ranges, instead of always chasing the pH around.
If the pH goes down, your plants are thirsty. If the pH goes up, your plants are hungry. Just top off with water or nutrient solution and you’ll never have to adjust pH again.
January 6th, 2010 at 6:00 PM
Red Icculus, that is great advice about letting the chlorine gas off, though makes me think that this would actually cause the pH to become even more alkaline. Though guess would happen if added directly to the tank over a period of time anyway and unfortunately shock the plants with a dose of chorine while you are at it.
I like the feed versus water philosophy. I have seen the advice on your site as well as others so definitely something I am going to go with. So you do not use any pH-up/pH-down type products for your tanks?
January 7th, 2010 at 10:15 AM
We have tab water with a pH of 8,3 here. After letting the water sit it goes down to ~7,5. I add some pH down (GH) aiming for a pH 5,8 (including fertilizers, which lower the pH themselves a bit). After that I top up with 7,5 water, so I get the same oscillation Red experiences.
January 8th, 2010 at 2:05 PM
Hey CVG-
I don’t use any pH up or down, but I haven’t tried this method with anything other than heavy feeders like tomatoes or peppers.
In theory, it should work with lighter feeders like lettuce, but might present problems when thirsty and burn them.
January 8th, 2010 at 7:25 PM
I would presume the same concept would occur just need to keep the concentrations down otherwise I agree burning the plants would definitely be a risk.