Each type of plant may be somewhat different in how they tell you what they need. But there are some common displays that will indicate if the plant is deficient in particular nutrients.

Even though you carefully prepare and feed your garden soil, mulch it with compost, and feed and water your plants, a plant may not thrive because it is not getting the nutrients it needs. If you have eliminated other possibilities such as extreme weather conditions, insects or disease, you need to evaluate the symptoms for possible nutrition needs. Rushing into corrective action or over correcting a problem could make it worse or even kill the plant. Wait and watch should be your first course of action.

In particular you should be observing for signs of deficiencies in fruits and vegetables which tend to have greater needs for certain nutrients. Also plants grown in containers are vulnerable as the frequent watering necessary for container plants washes nutrients out of the soil. If you have tested your soil for pH you may have found that your soil is highly alkaline or acidic which is quite important to certain plants and can also aid plant roots in taking in required nutrients..

The primary nutrients that all plants need are nitrogen, potassium, phosphorous, calcium, magnesium and sulpher. These macronutrients may be consumed in different quantities by each plant. Small amounts of manganese, iron, copper and zinc are also needed. As noted above, be sure you have the proper pH for your plants or the plant may not be able to actually take in the nutrients that are available in the soil. Water is also essential in taking in those nutrients so be sure to water adequately.

Symptoms of Nutrient Deficiency

Nitrogen Deficiency

Nitrogen (N) is a major nutrient required by plants but it is easily leached out of soil when dissolved in water. Frequent spring rains or heavy summer downpours can wash nitrogen out of soil leaving little or no nutrient for your plants. We commonly apply nitrogen as fertilizer. The nitrogen promotes growth as well as fruit, flower and seed development. It promotes the green foliage growth and good coloring.

Symptoms of nitrogen deficiency often first surface at the bottom of plants in the older foliage. The leaves begin to yellow and the rest of the foliage may fade to a lighter green. Growth will slow, and stems may also become yellow or grow weak and spindly. Applying a high nitrogen fertilize can quickly remedy the problem but be careful not to over apply which can quickly damage or even kill the weakened plant. A careful light dose of liquid fertilizer will allow the plant to take in the nutrient quickly. Then apply granular slow release fertilizer to continue the feeding. Mulching with compost will help to introduce nitrogen slowly over time.

Phosphorous Deficiency

Phosphorous (P) promotes healthy roots and growth of new plant shoots. It also aids in photosynthesis, seed germination and flowering. It is not common for soil to become depleted of phosphorous but is possible in regions that experience heavy rainfalls with clay soil.

Symptoms of phosphorous deficiency display first as slowed growth and fading or yellowing foliage. Young foliage may develop dark spots and the normal leaf color will not develop well and may appear tinted purple. The leaf tips may appear scorched.

Potassium Deficiency

Potassium (K) is used by plants to process sun energy and form sugars for protein (photosynthesis). This is critical for plants, as well as aiding in water uptake. Potassium also promotes flowering and fruiting as well as disease resistance and vigor. Potassium can easily wash out of soil especially in sandy or light soils. Clay soil does a good job of holding potassium in the soil structure.

Symptoms of potassium deficiency usually first appears on recently matured leaves. Edges will fade in color then brown. The scorching travels from leave edges toward the leave center. Leaf color fades to yellow. Flowering or fruiting will suffer. The established foliage damage is irreversible, but the remainder of the foliage can be maintained if potassium fertilizer is applied. Try sulphate of potash or kelp or other organic potassium source. Apply bone meal or superphosphate.

Magnesium Deficiency

Magnesium (Mg) is necessary in promoting plant enzymes to produce carbohydrates, fats and sugars through photosyntheses as well as regulate the absorption of nutrients. All this keeps foliage strong and healthy. Magnesium deficiencies are often cause by over application of high potassium fertilisers as the plants will take up the potassium rather than the needed magnesium. Tomato fertilizers are often higher than necessary and should be balanced. Light sandy soils may be low in magnesium and most often affects tomatoes, apples, roses and rhododendrons.

Symptoms of magnesium deficiency will first be yellowing of the leaves between the veining of mature leaves. New growth may be pale or yellow and develop dark spots. Leaves may drop. A dilution of 1/3 ounce of epsom salts per pint of water can be used as a foliar feed every 2 to 3 weeks but apply in overcast or very early or late in the day to avoid scorching leaves. Dolomite limestone or epsom salts can be applied to the soil to help long term.

Calcium Deficiency

Calcium provides structural support to the plant and to cell walls. It more or less holds things together properly as well as activating important enzymes. Calcium also signals the coordination of cell activity, directly influencing growth patterns.

Once calcium is taken into a plant it stays there until the plant dies back in fall. Calcium taken in by the roots will always be directed to be used in new growth. So if the soil has become depleted of calcium the symptoms appear in new growth. Extreme weather conditions that impedes transpiration (low temperatures or high humidity) can also impair the intake of calcium.

Symptoms of calcium deficiency are varied since the calcium directly affects cell growth and structure. Young leaves as well as young fruits that transpire little water will show symptoms first. Leaves will distort and curl or hook down and will brown at the tips and edges. Fruit formation will be distorted. All new growth of foliage, fruit and roots will be stunted. Blossom end rot in tomatoes is a gardeners lament. The first step is to check the fertilizer you use. Levels of magnesium, potassium or sodium that are too high may cause a calcium deficiency, but a level of calcium that is too high may compete with the intake of magnesium and potassium. Most calcium problems arise with the application of too much magnesium and potassium. Always use a well balanced fertilizer. If weather conditions are causing the problem, do nothing! Wait it out and hope that it changes quickly before too much fruiting damage is done.