Gardening Basics: Diagnosing Problems Looking At Leaves

The leaves of your plants give invaluable clues as to the health of your plants. Learn how to ID some common problems by looking at your leaves.

Shrub With Iron Deficiency

Can you tell what is wrong with this shrub?

At first glance you may notice that some of its leaves have a light green/yellowish cold while the other leaves are a darker green, which may give you an idea that something is wrong with it.

You may have heard the saying, “The eyes are the mirror to the soul” or the fact that doctors can tell a lot about a person’s health by looking into their eyes.  In the case of plants, the leaves are a window in which we can tell a lot of what is going on with them and whether or not they are suffering from nutrient deficiencies, environmental problems, pests and fungal diseases.

Today, let us look at what leaves tell us about nutrient deficiencies and problems with watering.

Iron Deficiency
Leaves displaying signs of iron deficiency.

One of the easiest nutrient problems to diagnose is iron deficiency, which is also called iron chlorosis.  The signs of iron chlorosis begin to show up in the newer growth of plants first with the leaves turning a lighter green/yellow color while the veins stay a darker green.

Iron is important to plant health and is one of the key components to produce chlorophyll, which is responsible for the green color of leaves.

The causes of iron chlorosis tends to be a problem in clay soils that are alkaline.  If plants are located in an area where the soil is too wet, they can also become deficient in iron.

Ways to correct iron deficiency should include correcting any problems with overwatering, if present.  A soil test will determine how alkaline your soil is and then you can amending the soil with elemental sulfur, which will help to lower the soil ph.  Add a chelated iron around plants can also help with problems with iron deficiency.  The best way to avoid problems with iron chlorosis is to use plants that are adapted to your area and soils that do not require large amounts of iron.

Leaves showing signs of nitrogen deficiency.
Leaves showing signs of nitrogen deficiency.

Like iron chlorosis, yellowing leaves are a sign of nitrogen deficiency, but with two major differences – the older leaves turn yellow and the veins turn yellow too.

Nitrogen is the most important element that plants need and when they don’t get enough, the rate of growth slows down and leaves begin to yellow.  Older leaves are affected first as the plant moves the nitrogen from them toward the newer growth, but eventually, even the new leaves will yellow too, if left uncorrected.

Signs of nitrogen deficiency can occur when there is little nitrogen present in the soil.  This can be due to wood shavings, sawdust or even compost that has large pieces of wood in it because it hasn’t decomposed enough is added to the soil.  Any available nitrogen in the soil is then used to help break down the wood instead of feeding the plant.  Another reason that some plants show signs of nitrogen deficiency is that they are ill-suited for the soil they are planted in – adding plants that have high nitrogen requirements into soils with little nitrogen.

Avoid problems with nitrogen deficiency by amending your soil with natural sources of nitrogen such as compost, aged manure and blood meal.  Fish emulsion makes a great natural, liquid organic source of nitrogen.  Lastly, select plants that are native or adapted to your region that can survive on the amount of nitrogen naturally present in your soil without having to add supplemental nitrogen.

Leaves showing signs of salt burn.
Leaves showing signs of salt burn.

Salt damage is a problem that can show up in arid regions where rainfall can be scarce.  Salts can accumulate around the root zone of plants that only receive shallow amounts of water that don’t permeate deeply into the soil.  This results from the fact that the soils have natural salts present and the supplemental water used to irrigate plants also has salts in them.  When small amounts of irrigation water are applied, the water quickly evaporates, leaving their salts behind.

Most plants do not like growing in soils with accumulated salts.  The solution to this problem is quite simple – water plants deeply to a depth of 1 1/2 feet or more.  This helps to flush out salts away from the root zone.  In addition, you can also select plants that can tolerate soils with elevated amounts of salt present.

Gardening basics usually turn to the easiest and most environmentally friendly way to avoid problems in the garden.  In this case, avoiding problems with nutrient deficiencies and salt burn is to select plants that are native to the area you live in where they are adapted to the conditions present without having to spend time and resources amending the soil.  To find a list of native plants that will grow in your area, click here.

Noelle Johnson
Noelle Johnson is a horticulturist, writer and certified arborist who lives and gardens in the desert Southwest. She is the CEO and owner of 'AZ Plant Lady,' an education company that aims to help people garden successfully in the desert climate. She is the author of the book, Dry Climate Gardening, and her byline has appeared in publications such as Birds & Blooms and Phoenix Home & Garden magazine. She is an instructor at the Desert Botanical garden and Tucson Botanical Gardens.