soil nutrients

Do plants get food from the soil?

June 22, 2022June 17, 2022Maryland GrowsLeave a comment

cabbage plant — Cabbage. Photo: A. Bodkins

People often say you have to feed your plants, but in reality plants make their own food through the process of photosynthesis, which yields oxygen and glucose. Glucose is the food that plants use for energy and growth, they don’t need us to actually feed them. Since plants can make their own food, they are called autotrophs. The green pigments in plants, called chlorophyll, capture light energy from the sun. The process isn’t nearly as simple as I’ve described it.

Plants can further be divided into two classifications, C3 or C4, which is determined based on how efficiently the plant can photosynthesize and whether the plant has to go through the process of photorespiration, which is required for C3 plants. This makes C4 plants, like corn, sorghum and sugarcane more drought resistant because of the complex processes that occur within the plant at molecular levels. The majority of plants are C3 plants. For more information on this topic check out the article from University of Illinois, The difference between C3 and C4 plants.

So why do plants need a soil that is sufficient in macronutrients and micronutrients if that is not their food? Well, the short answer is that nutrients help plants grow and keep them healthy so that they can photosynthesize efficiently. As the plant mass increases, the plant leaf size/surface area increases, which allows the plant to capture more sunlight and turn it into more food.

You can check out the Home and Garden Information Center’s webpage about fertilizer to learn more about macronutrients and micronutrients. Macronutrients are those elements that the plant needs the most of to be healthy. Water provides hydrogen and oxygen. Carbon dioxide provides oxygen and carbon which are part of the required macronutrients for all plants. The remaining macronutrients are provided by soil (unless the plant is being grown hydroponically, of course). Plants can only take up or use nutrients that are dissolved in soil water. This is why it is so important to make sure that your soil gets sufficient water. Some plants are called heavy feeders and this is generally in relation to their need for larger amounts of the macronutrients, especially nitrogen. Some examples are tomatoes, everything in the cabbage family, and beets. The University of Maryland provides more information on fertilizing vegetables.

tomato plant — Tomatoes (left) and a colorful cauliflower harvest with nasturtiums (right). Photos: A. Bodkins

yellow and purple cauliflower plants — Tomatoes (left) and a colorful cauliflower harvest with nasturtiums (right). Photos: A. Bodkins

By providing an optimum growing environment, through correct amounts of light, moisture, and nutrients, the plant will have the best chance at reaching its full potential. As I eagerly wait for the first produce from my vegetable garden this season, I want to be sure that all my plants reach their full potential and produce a large amount of food for me and my family to enjoy this growing season.

Please comment below with what you are doing this year to ensure that your plants are healthy and happy and growing well. Do you test your soil every 3 years or whenever you are planting a garden in a new area? Do you research the plant needs (full sun, part sun, or shade) before planting? What questions do you have about managing soil fertility and nutrients?

By Ashley Bodkins, Senior Agent Associate and Master Gardener Coordinator, Garrett County, Maryland. Read more posts by Ashley.

This year, the University of Maryland Extension Master Gardener Grow It Eat It Program celebrates the resource that supports all life on earth – soil! Look for soil education programs offered by your local Master Gardener program, and visit the Home & Garden Information Center website for more information about soil health.

What is soil pH and does it really matter to plants?

May 25, 2022August 11, 2023Maryland Grows3 Comments

Well, the short answer from a soil nerd (please note soil nerd is not the same as a soil scientist or soil chemist) is that yes it really does matter! Have you ever done the experiment with boiling red cabbage leaves and used that as a pH indicator? It’s a fun science experiment but probably wouldn’t work for determining an accurate soil pH.

People do not always see the benefit of getting their soil tested; however, if you take a good comprehensive soil sample, the information that you get from the analysis is invaluable. Not only will the results keep you from over-applying nutrients, which has economic and environmental benefits, but also it will ensure that your plants have all that they need right at their root tips.

In my opinion, the most helpful piece of information gained from conducting a soil analysis is the soil pH. PH is a measure of hydrogen ion concentration and tells you how acidic or basic/alkaline the soil is. Most vegetable garden plants prefer a pH between 6-7; therefore, acidic soils need to be amended with calcium carbonate (limestone). Acidic soils are indicated with numbers below 6 on the pH scale which ranges from 0 to 14. Soils in the Eastern US are often acidic, but the natural pH will depend on parent material and other soil factors, such as how the soil has been managed, what plants are growing there, etc.

It should be noted that some plants actually prefer acidic soils, such as rhododendron, azaleas, and blueberries. Also, some plant diseases, such as scab in potatoes, are worse at a higher pH. Lowering soil pH (often done by adding sulfur) can take several months and may need to be a multi-step process. It is a great idea to test garden soils in the fall, so pH-altering amendments have time to do their job. Here is a great cheat sheet to help you understand what your soil analysis results mean.

tomato plant with yellowing leaves on the bottom portion — Blueberry. Photo: C. Carignan

Another reason that pH is important is that it helps determine the availability of soil nutrients. Soil pH is linked to Cation Exchange Capacity (CEC), which is influenced by soil particle size and the type of parent material (rock). Clay soils will have a higher CEC (sites to hold onto nutrient ions) than sandy soils. CEC will be reported on most soil analyses. If the pH is not in the correct range, then many nutrients are not available to plants, even if you have applied ample nutrients. Thus, in order for the nutrients to support plant growth, it’s important to get that pH correct! This will provide both economic and environmental savings. Check out this link for a neat chart showing nutrients available and pH.

The third reason that it is important to check pH is because it can affect soil microorganisms, which are going to thrive at a near-neutral level. If the pH is too high or too low you will see a decrease in the number and activity of good soil bacteria, fungus, and more that help to break down organic matter and do amazing other things in the soil profile. (For more details on this topic, download PDF – Soil Acidity Impacts Beneficial Soil Microorganisms, from Washington State University Extension.)

Common questions about soil pH

Can pH change from year to year?

Some forms of nutrients —commercial fertilizers, compost, composted animal waste (cow, horse, pig, chicken manure), organic matter, the weathering of rocks, and even rainfall can alter pH. Fertilizers, depending on the type used, will alter soil pH at different rates. Refer to this PDF – Fertilizers and Soil pH from the University of California.

Can I use a home soil Testing kit?

I normally steer people away from these types of kits, just because there are so many inaccuracies, especially, if the kits were not stored at the proper temperature and the directions are not followed correctly, then the results may not be 100% accurate.

What about electronic soil testing probes?

I don’t have first-hand experience with these probes. I am sure that they do have a level of accuracy; however, I cannot justify the upfront cost. For most gardeners, soil testing every 3 years is sufficient, so in my opinion, it is easier to just collect the sample and send it to a laboratory.

By Ashley Bodkins, Senior Agent Associate and Master Gardener Coordinator, Garrett County, Maryland, edited by Christa Carignan, Coordinator, Home & Garden Information Center, University of Maryland Extension. See more posts by Ashley and Christa.

Plants not behaving as expected: vegetable garden edition

October 1, 2021January 28, 2022Maryland GrowsLeave a comment

Two of the vegetable crops I grew this year are known for loving the heat: okra and eggplant. I grow eggplant in pots on my deck, to avoid flea beetle infestation, and okra directly in the ground in my community garden plot. Both of them produced adequately over the summer. Now it’s fall; we’re having days in the 70s and nights in the 50s, and there are fewer hours of sunlight in the day. Time to pull the summer crops, right?

Except – boom! Both the okra and the eggplant are going gangbusters. More flowers, more fruits than in the hot summer months, by far.

‘Bride’ eggplant on a cool autumn morning

So why aren’t these plants following the rulebook? Do they not know how to read? Or have the rules changed?

Continue reading →

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