Prevention and Control Methods for Acid Damage and Alkali Damage in Garden Flowers

Different flower species require different soil properties. Generally, flowers native to the south, such as rhododendrons, camellias, orchids, gardenias, and osmanthus, are acid-loving flowers. Because they have long adapted to soil environments high in iron and aluminum and low in salt, once they are planted in calcareous or slightly alkaline soil, or watered over a long period with water containing calcium and magnesium, the acidic potting soil will become alkaline, the leaves will easily develop iron-deficiency chlorosis, the plants will grow poorly, and they may even die. Some flowers that prefer neutral or slightly alkaline conditions, such as chrysanthemums, carnations, Chinese roses, and gladioli, are prone to acid damage when soil acidity is high, which obstructs root growth and causes poor aboveground growth. Therefore, different corrective measures must be taken for different situations.

When acid-loving flowers are grown in the north, the soil must be improved. Generally, 0.5-1.0 g of sulfur powder or 1.5-2.0 g of ferrous sulfate should be added per kilogram of growing medium, mixed and piled for 2 weeks before potting. If water containing calcium and magnesium is used to water the flowers, it must be treated by dilution with water; a 0.2% ferrous sulfate solution can be added and used for regular watering, and it should be mixed fresh and used immediately to prevent the ferrous iron from oxidizing and losing effectiveness. In fertilization, acidic or physiologically acidic fertilizers should be chosen, such as potassium nitrate, ammonium nitrate, ammonium sulfate, and superphosphate; alkaline fertilizers such as plant ash should not be applied. Although urea is a neutral fertilizer, after being applied to the soil it converts into ammonium bicarbonate, making the soil locally alkaline, so it should not be applied in large amounts. However, when urea is used as a foliar topdressing, as long as the concentration is appropriate, the results are still satisfactory.

For flowers that prefer neutral or slightly alkaline conditions, because the root system continuously secretes acidic substances during growth, or because acidic or physiologically acidic fertilizers are applied over a long period, the soil will become acidic, which can also affect the normal growth of the flowers. Alkaline fertilizers such as lime, limestone powder, and plant ash can be applied to reduce soil acidity and meet the flowers' requirements for soil acidity. In particular, for flowers such as carnations, proper application of limestone powder also has the effect of making the flower colors more vivid.