Plants may need to be fertilized while in outdoor retail yards. Rainfall and watering with plain water will leach out nutrients and plants will exhibit deficiency symptoms such as yellow or reddish foliage. Note that reddish foliage could also be due to recent cool temperatures. If no additional fertilizers are applied, plant quality will quickly deteriorate especially plants that will not be transplanted, such as hanging baskets. Plants in packs, 4-inch and other small containers are also susceptible to nutrient deficiency.
A reminder that zonal and seed geraniums, American marigold, and all types of impatiens are susceptible to iron/manganese toxicity, a nutritional disorder associated with low growing medium pH. This problem is sometimes called "bronze speckle" due to the appearance of numerous small brown spots on the edges of the leaves of geranium and marigold. The target pH range to prevent toxicity is 5.8-6.5. If the pH is lower than the target range the risk for toxicity increases because at low pH too much iron and manganese becomes available to these plants.
Foxglove aphids have been reported on Ipomoea ‘Marguerite’ and other aphids on ornamental grasses, many perennials, dahlias, zonal geraniums and tomato bedding plants. Watch for aphids including the foxglove, green peach aphids and melon aphids. Foxglove aphids tend to feed first on the underside of the lowermost leaves and then migrate to the flowers. Because foxglove aphids reproduce faster at 50˚ to 60˚ F than at 77˚ F, they are more of a problem if your crops are grown cool.
Cloudy, rainy weather, cool nights and greenhouses full of plants provide an ideal environment for Botrytis. Botrytis symptoms may include leaf spots, flower blights, bud rots, stem cankers, and stem and crown rots and can be mistaken for other causes.
Tarsonemid mites including cyclamen mite and broad mite can cause serious damage to a wide range of greenhouse crops such as New Guinea impatiens, garden impatiens, dahlias, gerbera, ivy, lantana, snapdragon, verbena, zinnia, peppers and other vegetable plants.