Lauterbach: Yellow leaves? Add some iron

May 9, 2013 


Add wood chips to soil to help it remain moisture, and reduce the chances your tomatoes and peppers will develop blossom end rot.


Treasure Valley gardeners know our soil is alkaline, too alkaline for some plants to grow. Nationally published magazines and references routinely advise adding lime or wood ashes to soil because they're expecting soil to be acidic, not alkaline, but we can't add those items without causing ourselves unneeded plant death.

Soil alkalinity means one thing that you should take care of right now if you have fruit-bearing shrubs or trees: Give them supplemental iron. Alkaline conditions mean plants can't take up as much iron as they need. Fruit trees show this deficiency in yellowing of leaves.

As soon as blossoms fall, spray foliage with chelated iron, available in garden centers in bottles. Spray leaves again within 10 days and a third time before June 15, preferably in May. This is much easier than trying to change the soil's pH, and is the routine followed by commercial orchard owners in this area.

The reason to spray now instead of when the leaves turn yellow is that the leaves now are sufficiently tender to take in the iron. Later they grow tougher and waxier. Once leaves turn yellow, it's nearly impossible to green them again.

Leaves on container plants, such as citrus, may turn yellow if they're overwatered, too. Monitor water with a moisture meter, usually $15 or less at garden stores.

This iron feeding of leaves must be done every spring, at the times specified above.

Our soil lacks magnesium, so a one-time application of two tablespoons of Epsom salts in a gallon of water is beneficial to many plants, especially roses and tomatoes.

Another apparent nutrient deficiency is calcium. Our soil is generally not lacking in calcium, but unless the soil is moist - neither dry nor sopping wet - it can't take up calcium for plant needs. Unless you solve this problem, your tomatoes will have flattened, brown papery bottoms and peppers will have similar problems near the bottoms of the peppers, not on the blossom scar, both problems called blossom end rot (BER).

The way to handle this is with infrequent deep watering and a moisture-holding mulch such as grass clippings that haven't been sprayed with herbicide, shredded paper or leaves, wood chips, cardboard, several layers of newspaper, or even soil aid. Any soil cover that will retard moisture evaporation will work.

By infrequent watering, I mean once a week as long as the daytime temperatures are under 100 degrees; when temperatures rise above 100, I water about every third or fourth day.

Other causes of BER are high nitrogen fertilization and accidental root pruning by cultivation, as well as vulnerability. Plum tomatoes are especially prone to BER.

Sunscald on peppers leaves light brown papery parts of the fruits or flabby white tissues that occur where the fruit is directly exposed to the sun. BER looks similar to the brown papery parts, but it usually occurs lower on the fruit. Sunscald on tomatoes just turns them white and inedible. Avoiding sunscald is a good reason NOT to prune tomato plants.

Speaking of pruning, do not prune any tree after its buds begin to open, but you may prune in mid-summer, spurring less vegetative growth then than you do when the tree is dormant in late winter. The two worst times to prune a fruit tree is when it's breaking open its buds and when it's losing its leaves.

Send garden questions to or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.

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