A common problem often diagnosed this time of year with spring crops is excess soluble salts. Generally, this is a result of too much fertilizer in relation to the plants needs. Inadequate watering or leaching, or poor drainage can also result in high soluble salts.
It is that time of year for extreme temperatures and weather conditions. Monitor the weather forecast and avoid moving cold tolerant annuals and herbaceous perennials outdoors if a hard frost (colder than 28°F) is predicted at any point within at least three nights of when plants would be put outside. Avoid placing plants in low-lying areas because frost will more likely settle in these areas. Be prepared to cover plants if temperatures go below 28°F.
Watch for two-spotted spider mites on lemon balm, mints, mandevilla, cordyline, ipomoea, New Guinea impatiens and other crops. Spider mites may come in on incoming plants or have over-wintered in your greenhouse. Look for dull stippled foliage on plants particularly in warm, dry locations in your greenhouses such as near steam pipes, furnaces, heaters or overhead hangers. Symptoms of mite feeding are often observed before mites are noticed. Use a 10 to 20x handlens and look on the underside of mature leaves, especially along the midvein for eggs, immature stages and adults.
Cloudy weather and cool nights provide ideal conditions for Botrytis blight. When temperatures drop during the night, the colder air cannot hold as much moisture, so it condenses on the foliage and flowers, which encourages Botrytis.
When growing vegetable plants this spring, consider the disease interaction between vegetable plants, herbs and ornamentals in greenhouses. While it can be difficult to devote valuable space to specific crops, if possible, maintain vegetable plants and ornamentals in separate greenhouses so diseases will have less opportunity to move from vegetatively –propagated ornamentals to seed-propagated vegetables. Separate greenhouses also make it easier to use different fungicides for ornamentals vs. edible crops.