pH needs of plants in soil or hydroponics

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

21 Responses to “pH needs of plants in soil or hydroponics”

  1. Red Icculus Says:

    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.

  2. The Cheap Vegetable Gardener Says:

    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?

  3. Ragnar Says:

    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.

  4. Red Icculus Says:

    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.

  5. The Cheap Vegetable Gardener Says:

    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.

  6. Davilyn Eversz Says:

    I am a commercial organic grower. I also live in the desert with a 8.3 ph. I use food grade citric acid to lower ph. I was using ph down but because of the heat it was highly unstable and rose again quickly. Once I changed to the citric acid is has become quick and easy. Even in my 55 gallon reservoirs it rarely takes more than 1-2 TBS. You have to search around, a lot of people charge a lot for it. I get it at For 40#’s it is $100. Plus citric acid really helps the veggies assimilate the nutrient.
    If anyone has had problems with tomato fungus I can help with that too.

  7. Jeff Says:

    I am in the process of developing my garden so not sure on the PH levels. I live in the UK and I believe we live in a hard water area so watering could have an effect on the tamatoes that I plan to plant..

  8. Ed Ward Says:

    “Now when it comes to hydroponics this is entirely different.”
    Yes. I’ve heard when growing hydroponically when pH rises above 6.5 some of the nutrients and micro-nutrients can begin to precipitate out of solution and can stick to the walls of the reservoir and growing chambers.

  9. BOB Jogger Says:

    @Davilyn Eversz – Thanks for that info. I’m in the desert too and am just getting started (not on a commercial level, just for myself). I found I did have a pH issue and it sounds like I’ll have to give your citric acid trick a go. Hopefully it’ll work for me just like it does for you. Thanks again.


  10. Taylor Says:

    The more artificial the environment, the more likely you are going to have ph issues or at least be concerned that they could exist.

  11. Dover Says:

    Most seem to be in the 6.0 to 7.0 range. Frankly, this isn’t something that I’ve considered – could be why I always have a problem with tomatoes.

  12. Steve Warwick Says:

    This is a really useful table. I always reckon on taking the ph in the garden, but it isn’t always so easy to adjust it, espcially if you’re about to plant. Sometimes, good intentions and good planning don’t seem to work all the time!

  13. blue blink Says:

    here in our country many people planted differnt crops because the soil is good!!! according to my research about when most people think of HYDROPHNICS, they think of plants grown with their roots suspended directly into water with no growing medium. . right?

  14. John Kelly Says:

    I am just starting to get into growing some of our own vegetables and I have a question about this PH level. How do you measure it and how do increase or decrease it if needed?

  15. Dan Says:

    “I am just starting to get into growing some of our own vegetables and I have a question about this PH level. How do you measure it and how do increase or decrease it if needed?”

    +1 We’ve just started our first backyard garden and have no idea how to measure the PH level. Any advice would be greatly appreciated!

  16. Sammy-J Says:

    @dan. You should be able to buy a very simple and inexpensive kit from any good garden store. They are the sort of thing I really on in my own veg garden. The trick is to carefully record what’s going on and plant something suitable.

  17. Dhiraj Says:

    I’m a diabetic and I’ve done a lot of research on broccoli which is very good for diabetes.I’ve a feew broccoli plants in my garden.
    Calcium is also important to broccoli. You can add crushed limestone to your bed, but keep in mind this will increase the soil pH. The ideal pH for broccoli is a neutral 7.0


    From Insulin Storage Guidelines

  18. Amber Says:

    @Dan Just go to the nearest garden store and ask the store owner or manager, I’m sure they’ll be able to give you a few tips .

  19. Shong Says:

    To achieve healthy, vigorous plants for a pleasing landscape or a productive garden, the plants require optimum soil conditions that may be specific to the type of plant. Nutrient levels, drainage condition, and soil pH are examples of soil conditions that are important to consider when choosing plants and managing your landscape. This fact sheet discusses the pH factor alone; remember that many other factors are important for optimum growth.

  20. mely Says:

    Few of the plants mentioned above are of my favorites. I never thought that there are actually required acidity of the soil to be planted for it to grow, because here in our country few of those mentioned plants just grow anywhere. All you have to do is to have seeds of it and dig in the soil and put it. that’s it! after a week it will grow then.

  21. Andy Scott Says:

    Many things to learn. I am good i hydroponics but was not sure of most on PH levels.

    Will help me a lot.

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