Do you have a plant that looks nutrient deficient regardless of how much fertilizer you apply? Are your plant’s leaves yellow with green veins? Is the new growth growing in almost white? If so, you likely have a soil pH problem.
Nutrient levels, drainage, soil texture, and light exposure probably get more attention than soil pH. However, understanding soil pH and how it affects your plants is an important part of gardening. This is because different plants require different pH levels. It makes the difference between whether they thrive or die. Plus, if your pH is incorrect, you are wasting your money trying to fertilize that yellow plant. No amount of fertilizer will help as the nutrients are bound up and unavailable to the plant.
Container grown plants are particularly susceptible to pH caused problems. This is due to the decreased buffering and nutrient holding capacity of soilless mixes and the small container sizes as compared to the earth’s soil mass. You also irrigate your containers more frequently that you do the soil. This means that the pH of your irrigation water can have a larger impact on your container plants.
PH is simply the measure of how acidic or basic the soil is measured on a scale of 0-14.
A lower number is more acidic, a higher one is more alkaline. At very high or low pH, many nutrients form insoluble complexes that make nutrients unavailable for plants to take up. For this reason, most plants prefer to have a neutral to slightly acidic pH (between 6.0.7.5). This is the range in which most plant nutrients are most available.
The main symptom of pH problems are nutrient deficiency symptoms.
Image title: Soil pH effect on nutrient availability by CoolKoon licensed under Creative Commons Attribution 4.0 International
Having a nutrient deficiency despite fertilizing makes sense since pH affects the availability of nutrients. One of the most common nutrient deficiencies seen from pH problems is iron deficiency of acid loving plants such as blueberries and azaleas.
Nutrient deficiencies can be confusing. Iron deficiency looks similar to nitrogen deficiency. It is manifested by the yellowing of leaves. However, it is easy to tell apart from nitrogen deficiency by looking at the location of the yellow leaves. Nitrogen deficiency shows up on old leaves. Iron deficiency will show up on new leaves which will be yellow with green veins. In severe cases the leaves can even turn completely white.
Other pH caused nutrient deficiency symptoms such as brown, dead leaf edges or plant dieback are common. You may also see stunted growth or deformed leaves. These symptoms are also caused by various other pH induced nutrient deficiencies.
Soil pH can be affected by variables such as your location, irrigation water, and how the soil was previously managed.
Generalizations can be made about certain geographical areas, but this is not a good way to determine your soil amendment needs. For instance, if soil in a region is typically acidic, but it has been treated with lime for years and years, that particular patch of soil may actually be extremely alkaline. Therefore, you cannot know for sure what the pH of your garden is without getting a soil test. It is important to get a soil test done in your garden before you add any amendments so that you don’t accidentally make an existing problem worse.
Soil tests are easy, and inexpensive to do. They will tell you not only the pH of your soil, but also how much organic matter is present, and what other nutrients are excessive or deficient. If you tell the lab what crop you will be growing when you send the soil test, they will make fertilizer recommendations for you. That way you can fertilize your plants with what they actually need for healthy growth and production.
If your soil pH is not ideal, you can alter it.
Don’t be discouraged if your test results show excessively acidic or alkaline soil. If you commit to altering the pH level, it can be changed. This can be done by applying sulfur to lower it or lime to raise it. Adding amendments to change the soil pH should be done carefully and slowly over time with pH tests done periodically.
Soil pH changes slowly, so you will not see an immediate difference after applying either lime or sulfur. You do not want to over amend the soil. If you aren’t careful and make the mistake of driving your pH excessively high or low by improperly amending the soil, it can take decades to fix the problem.
It is easier to make the required frequent amendments to maintain an altered pH when planting annual crops where the soil can be amended and tilled yearly. It is more difficult to alter the pH of the soil in an already established planting, or to maintain the pH in a permanently planted bed. Thus, it is important to do soil testing, and proper bed preparation before planting a new bed of perennial plants.
It is good to keep in mind that any pH change you inflict on your soil will be temporary.
You will have to repeatedly apply lime or sulfur to maintain the pH you adjusted the soil to as the soil will wish to revert to its natural state (the pH of all the soil surrounding the beds you amended).
If you wish to grow certain fruits and vegetables, you will be stuck with adjusting pH to meet their needs. For example, if you wish to grow blueberries, you have to figure out how to get them very acidic soil or they will die. There is no blueberry that can grow in alkaline soil.
However, this is not the case with ornamentals. There is a wonderful range of ornamental plants that thrive in soils that range from extremely acidic to extremely alkaline.
Right plant, right place
It is our opinion that when planting ornamentals you should select plants suitable to the natural pH of your soil. Save yourself the headache, expense, and disappointment of fighting an uphill battle. If you are unsure what plants would thrive in your particular soil, a quick internet search will net you a list of options.
If your pH is on the acidic side, you should focus on acid loving plants. There are a good number of commonly grown landscape and edible plants that prefer to be grown in a more acidic soil. These include plants such as blueberries, azaleas, potatoes, hydrangeas, camellias, and many evergreens. There are of course dozens and dozens more plants that prefer acidic soil as well.
There are also many plants that prefer neutral to alkaline soil. These include butterfly bush, deutzia, forsythia, lilac, viburnum, and weigela. If you have highly alkaline soil we would highly recommend planting alkaline tolerant plants. It is not as easy to lower soil pH as it is to raise it as lime for raising pH is much more widely available.
Now with the exception of a few acid loving plants, you don’t have to go crazy worrying about pH.
Most plants will grow well within a range of pH levels. They don’t need the soil to be an exact pH to thrive. As we said before, most plants would prefer a slightly acidic to neutral pH between about 6 and 7.5. This is a good range to strive for. If your pH is in or near this range and your plants are doing well, you should make no changes.
Irrigation water can have a huge effect on the soil pH
Yes, that’s right, your water may be adversely affecting your plants. If you have highly acidic or alkaline irrigation water, and you irrigate frequently, over time the irrigation water can alter your soil pH. Irrigation water can alter the pH just as much as if you had added sulfur or lime to your soil. If your soil pH is where you want it, it is a good idea to make sure that your irrigation water is a similar pH. If it is not, you should use a different water source or adjust the water pH before irrigating with it. The last thing you want to be doing is watering your hard earned acidic soil with high pH irrigation water.
Container growing can be the solution to pH problems
We mentioned before that pH of container plants needed to be more carefully monitored because they had decreased buffering capacity as compared to the soil in your garden. This drawback can also be used to our advantage if we wish to grow plants that will not thrive in our regular soil. If for example you have very alkaline soil and wish to grow blueberry plants, you may be better off planting them in containers rather than trying to amend the soil.
A 15 or 20 gallon container can grow a large blueberry bush for a long time. The pH in the container can be easily maintained by using acidic fertilizer and/or acidic irrigation water allowing your plant to thrive. Whereas to plant in the ground, you would need to start soil pH adjustments at least a year prior to planting the bushes. Once the desired pH is obtained you would need to make frequent sulfur applications to attempt to combat the soil pH drifting back to alkaline in your garden.
Lastly, if you aren’t having any problems, don’t stress about soil pH. Zillions of plants in your neighborhood are growing just fine in unamended soil. However, checking your soil and water pH is something to consider if you are having problems growing healthy, productive plants. If your plants are failing to perform as expected a soil pH test should be in order.
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