First Aid for Growers in the East
By David G. Leach
In some parts of the eastern United States this has been the wettest summer for more than a century. Districts which normally receive ten to fourteen inches of rain in June, July and August have received more than twice that amount, and records going back to the beginning of the weather bureau have been broken.
The extraordinary rainfall, continuing into late summer, has prevented the normal maturation of plant tissues and there is every prospect that countless rhododendrons will be killed or seriously injured by the advent of cold weather. Turgid with sap of low carbohydrate content, they will die when the expansion caused by the first freezing temperatures forces water out of the cells into the intercellular spaces. It can not be recovered fast enough upon thawing to prevent the collapse of the cell walls and thus the tissues are destroyed.
A few years ago, in experiments in Georgia, the usual 25% loss over winter of Camellia 'Alba Plena' in small stock in nursery beds was prevented by the application of 25 pounds per 1,000 square feet of potassium sulphate several weeks before the first hard frosts. Such a result was surprising since potash does not normally hasten hardening-off. In all probability the beneficial effect came from increased vigor of the plants caused by the supply of this element after a rainy summer had leached out reserves in the soil.
In any event the consequence of the first experiment prompted further comparative trials with chemical nutrients to determine their effect in hastening the maturity of plant tissues. Plots were treated with super-phosphate alone, with potassium sulphate alone, with a mixture of the two, and finally with a combination of super-phosphate, potassium sulphate and magnesium oxide. A check plot received nothing. Of the four treatments the formula containing super-phosphate, potassium sulphate and magnesium oxide was much more beneficial than any of the others and its effect in promoting the maturity of plant tissues was conclusive. C. Barbre has been using it effectively on azaleas and rhododendrons in his nursery in the St. Louis district for years.
Rhododendron growers in the East can use this information to their immense benefit for the protection of their plants against the cold which may otherwise prove to be calamitous this year. In areas served by the Reliance Fertilizer Company a fall conditioner containing phosphate, potash and magnesia is available ready-mixed for convenient use. Similar formulations may be offered in other regions by progressive fertilizer manufacturers. If not, the grower can buy almost anywhere a 0-25-25 fertilizer mixture and add 2% by weight of magnesia (magnesium oxide) or Epsom Salts (magnesium sulphate). I am applying this home-mixed formula this year to specimen plants growing in a soil rich in humus at the rate of 50 pounds per 1,000 square feet. Small seedlings up to six or eight inches tall growing in ground beds receive two applications two weeks apart at the rate of 25 pounds per 1,000 square feet. Since the effect of chemical fertilizers may vary widely according to soil and other local conditions, growers elsewhere may wish to make two applications at half rates, observing the effect of the first before making the second.
It is important that the formula contain a magnesium compound since this element substitutes for calcium in acid soils to aid in the translocation throughout the plants of the phosphates which play such an important role in the hardening-off process.