Magnesium deficiency in tomato plants

Magnesium-deficient tomato leaves show advanced interveinal chlorosis, with necrosis developing in the highly chlorotic tissue. In its advanced form, magnesium deficiency may superficially resemble potassium deficiency. In the case of magnesium deficiency the symptoms generally start with mottled chlorotic areas developing in the interveinal tissue. The interveinal laminae tissue tends to expand proportionately more than the other leaf tissues, producing a raised puckered surface, with the top of the puckers progressively going from chlorotic to necrotic tissue.

Role of magnesium in tomato plants

Magnesium is required for many processes including transfer of energy and protein synthesis. With 20-25 % of the plant’s total magnesium localized in the chloroplasts, it is particularly important for chlorophyll production.

Magnesium is particularly important in ensuring even ripening of well-formed fruit.

Vegetative Growth - Maximize concentrations in leaf tissue prior to flowering
Flowering - Fruit Set Improve flowering and crop production – maximum requirements are at this stage
Fruit Ripening - Maturity Maximum requirements are at this stage for quality fruit production

A regular supply is needed throughout the life of the crop. Up to 54lb/ac of magnesium is used by a tomato crop. Magnesium uptake can be depressed by an excess of other cations, so it is important to maintain a correct balance. Particular care is needed in fertigation systems.

Symptoms of magnesium deficiency

Symptoms of magnesium deficiency start at the bottom of the plant on older leaves and then works their way upward. Fruits appear to ripen evenly but maturity is often delayed. Deficiencies may also occur in the middle of the plant during heavy fruit load, but this is usually transient. Where deficiencies are less severe, older leaves look brittle and their interveinal tissue is curled up. Where deficiencies are severe, chlorosis between the veins progresses from the margins to the middle of the leaflets. The small veins also become chlorotic, but the bigger veins remain dark green. With ongoing magnesium starvation, the interveinal chlorosis becomes more intensive, the color turns to bright yelloworange and necrotic spots may appear, which can grow together into brown bands. Finally, the older leaves die and the whole plant turns yellow and fruit yield is severely reduced.

Remedy

In the short term, apply Epsom salts as a foliar feed in summer. Dilute the salts at a rate of 20g of Epsom salts per litre of water (1/3oz per pint) plus a few drops of liquid detergent. Apply two or three times at fortnightly intervals, spraying in dull weather to avoid leaf scorch. In the long term apply to the soil around the roots either Dolomite limestone (calcium-magnesium carbonate) at 100g per sq m (4oz per sq yd) or Epsom salts (magnesium sulphate) at 30g per sq m (1oz per sq yd). Dolomite limestone will make the soil more alkaline, so should not be used around ericaceous (acid-loving) plants such as rhododendrons or camellias, or where the soil is already alkaline.

A gardener's voice

Read this article to know more about magnesium deficiency-

About four days ago I noticed my tomato plant's leaves were turning yellow, but the veins were still green. This is a sure sign of a magnesium deficiency and can kill plants if not treated. But, luckily, its easy and cheap to cure. 

Potted plants and seedlings in trays can experience soil depletion. Meaning, the plants soak up all the nutrients in the soil and will start to show signs of stress and nutrient deficiency. It's important to keep those plants "fed" with fertilizers, and there are lots of organic options to help keep plants healthy. Tomatoes are especially "hungry" plants, during their growing and fruit producing stages they are what I call "nutrient supersoakers". Tomatoes like plenty of nitrogen, and magnesium. Before transplanting your tomatoes outside dump wood ashes on your soil and mix in with the soil to prevent a strong wind from carrying away your ashes. Ideally, you want to let the ashes "soak" into the soil for a few months, but if you are pressed on time, some ashes are better than none. We have a wood stove that we use for heat over the winter and we have been dumping wood ashes on our garden beds all winter, the snow was excellent for packing the ashes down into the soil for deep soaking. Giving your plants magnesium is as easy as buying Epsom Salt. Epsom Salt is actually Magnesium Sulfate, not salt, so it is an excellent organic source of magnesium for your plants. 

Once I noticed the deficiency in my tomato plants, I went out and bought some Epsom Salt. If a magnesium deficiency is left untreated, the leaves will eventually turn yellow, and the veins, and the leaves will die and fall off. I mixed one to one and a half tablespoons with warm (not hot) water in a gallon jug and shook the jug until most of the "salt" had dissolved. The nice thing about Epsom Salts is that it dissolves quickly. I poured the water into one of the empty cells in my seed trays (I like to leave an empty cell to check water levels). Once the water level in my tray reached a little less than half, I poured the remaining water into a spray bottle and gently sprayed the tomato leaves with the water/salt mixture. By filling the seed tray and spraying the leaves, I am helping ensure that both the roots and the leaves receive the magnesium immediately. 

For the past four days, I have gently sprayed the water/salt mixture on the leaves. Water levels in my seed tray show the plants still have plenty of water. After four days, I saw significant improvement in the health of my plants. The leaves are still slightly yellow, so I will continue my treatment until the yellowing has disappeared.

Healthy plants = successful transplanting. I am planning (weather permitting) to transplant my tomato plants outside in my garden beds in three to four weeks. If my plants are to survive the stress of transplanting, they need to be as healthy as they can be. Good luck on your spring gardening!

 Now you may have known what to do with the plants with magnesium deficiency. So enjoy!