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Are Your Plants Hungry? The Importance of Understanding pH

Posted May 15th, 2008 by Amanda Sylvie in

If you provide your plants with a well-balanced fertilizer they will grow well, right? Maybe. How do you know if your plants are absorbing the nutrients you are providing? Sometimes it is difficult to know if plants are receiving their optimal nutrition until there is a decline in growth or blooming.  If you are hoping for a bumper harvest of fruits or vegetables, you don’t want to miss your chance just because the plant was not as healthy as you thought it was.

For improved nutrient uptake, it is important to monitor the pH of your soil and the water you use to fertilize. The pH scale for plants ranges from 4 to 10 with 4 being the most acidic and 10 being the most basic or alkaline. During tests showing absorption rates of the twelve plant nutrients (Nitrogen, Phosphorus, Potassium, Sulfur, Calcium, Magnesium, Iron, Manganese, Boron, Copper, Zinc and Molybdenum) plants absorbed these nutrients best when the soil pH was slightly acidic. Seven is neutral on the pH scale and the ideal soil pH range for nutrient absorption is 6.0-7.0. If the soil is too acidic, the plants may not absorb enough Nitrogen, Phosphorus, Potassium, Sulfur, Calcium or Magnesium, but the plants may absorb too much Iron, Manganese and Boron. Ideally, plants are able to absorb all of the available nutrients in the ratios the particular plant requires. It is important to note, however, some plants prefer more acidic environments, such as blueberries and azaleas that grow best in a pH range of 5.0-5.5.

As you attempt to determine if your plants have access to a variety of nutrients, here are a few things to consider:

Soil Quality

It is important to analyze the quality of your soil by determining the soil’s pH, if the soil allows for adequate drainage, and the composition of the soil. Once you have a better understanding of your soil, you can then begin improving the soil for the type of plants or crops you are growing. Depending on your soil analysis, routine improvements include addition of lime, bone meal, sulfur, compost, manure, or peat moss.  These are just a few ideas –your local garden center, mail order company, or online retailers should be able to offer soil amendments and ideas for safely incorporating them into your soil.

Residing in San Antonio, TX, our soil is full of limestone which means we have a lot of calcium and the soil typically drains well. As a result, we have to try to bring the soil pH down to a more acidic level and we also have to increase the amount of Ironite that we use since most of the iron washes away during rainstorms and it is less available to plants in alkaline soils. If soil pH is too high or too low, the plants will not absorb many of the nutrients.  As a result, your plants will likely suffer and create the environmentally unfriendly fertilizer runoff.

Water Quality

The water used to hydrate plants can also impact nutrient absorption. This is especially important in hydroponics and when raising orchids. Since both utilize soilless growing methods, the pH of the water will determine which nutrients are available to the plants. Well water, softened water, distilled water, reverse osmosis water, or rainwater may each have a different pH. The pH further deviates when fertilizers and nutrient supplements, such as Superthrive root stimulator, Mineral Matrix micronutrients or Pro-TeKt silicon protectant, are added to the water.

Temperature

Nutrient uptake by plants is also affected by temperature. Generally, as temperatures increase, so does the intake of nutrients. However, various plants have temperature ranges optimal for that particular type of plant. Tomatoes are warm-loving plants and will not begin to thrive and take in adequate nutrients until they are quite toasty.  Yet broccoli suffers in warmer temperatures and will not begin to provide an abundance of tasty green heads until cooler temperatures abound.

A majority of popular plants enjoy warm temperatures and require more nutrients during their high-growth periods. This is why controlled-release fertilizers such as Nutricote are so popular. As temperatures increase, the pores on the special gray resin coating begin to expand, releasing increased levels of fertilizer to correspond with increased needs of the plants.

When growing outdoors, gardeners increase the length of their growing season by keeping plants warm with special gardening blankets, mulch for insulation and warm frames. Greenhouse growers use heaters and humidifiers. When growing indoors, many of the HID (High Intensity Discharge) lighting such as HPS (High Pressure Sodium) lights create high heat levels; however, growers using low-heat LED or fluorescent lighting may need to supplement heating by using heated seedling mats to encourage growth or flowering.

EC Levels

EC (Electrical Conductivity) is the ability of a solution to conduct electricity. EC is related to salt levels and can dramatically affect the growing environment.  Higher salt levels result in higher EC and lower salt content results in a lower EC. Plants cannot effectively absorb water that is too high in salt content and they can show drought symptoms even if they are thoroughly watered.  It is important to note fertilizers and supplements raise the EC content of water. Also, if your plants are not absorbing many of the fertilizer nutrients provided, perhaps due to excess fertilizer levels or incompatible pH levels, EC levels in the surrounding soil may be too high. As a result, root growth and development will decline.

When considering EC, gardeners often refer to TDS (Total Dissolved Solids) as well. In the most simple definition, TDS measurements are very similar to EC, but are expressed in ppm (parts per million). The benefit of having a meter that tests TDS is the meter does the conversion from EC (expressed as µS/cm) to ppm for you.

Evaluating the Environment

There are a couple of ways to evaluate the growing environment you are providing for your plants. Local garden centers or your extension office may offer a soil analysis which will show the pH value of the soil, as well as levels of Potassium, Phosphorus, Calcium, Magnesium, Zinc and Manganese. They will also explain what soil amendments will improve the conditions for your plants. It is quite possible for the soil quality to differ in the various gardens or areas of your yard (vegetable garden vs. rose garden vs. turf), so it is helpful to have an analysis done of samples from multiple areas, especially if you have noticed problems in a specific area.

To evaluate pH, water quality, temperature and EC levels, testing equipment such as a handheld meter is most convenient. Other options to the convenient handheld meters are agricultural test kits and direct soil meters. Agricultural test kits are reasonably priced and easy to use. They can be purchased for testing single parameters, such as pH or iron, or as a multiparameter kit that will test Nitrogen, Phosphorus, Potassium and pH.  A field-ready option to making slurries is the Direct Soil pH and Temperature Kit (HI 99121) that provides rapid, accurate measurements when the probe is inserted directly in the soil.

Know Your Soil

What you decide to measure and why will depend on your growing conditions and the types of plants you raise. In hydroponic systems, growers most often test the water solution for ideal pH, temperature and EC or TDS in addition to frequently monitoring the fertilizer nutrient concentration. Orchid growers may benefit from testing the pH of the water they use for fertilizing as the fertilizers and supplements may dramatically alter the pH and hinder nutrient absorption. Growers utilizing a greenhouse may prefer to use a test kit for only the plants that show stunted or abnormal growth. Outdoor gardeners may take soil samples from various garden locations in their yard to determine which planting areas need a specific type of conditioning. Whatever type of gardening and growing you are engaged in, keep it flourishing with ideal conditions.

Want more information? Read these articles:

Is the pH of a Hydroponic Solution Really That Important?

pH Testing in Hydroponics Explained

pH? Widely Used, Little Understood

The Role of pH in the Garden

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