Pictured is an example of high pH, low micronutrients on the left.
Spring is a very busy time for most greenhouse growers. Multiple activities are taking place simultaneously: potting, shipping, merchandising, spacing, growing, monitoring crop quality, spraying, etc. Weather is ever-changing and can throw a monkey wrench into even the best of scheduling plans. With the soaring cost of heating fuel, growers are trying to pack more plants into their growing spaces. In northern climates, growers are waiting longer to start their crops, further compressing the spring growing season.
Consumer demands dictating the need for crop diversity also continue to increase, presenting the grower with a multitude of diverse nutrient requirements in the same operation, taxing injector and plumbing setups. Combination containers can result in plants with different nutrient requirements being grown in the same pot. It is easy to see how crop quality problems can arise in the spring. Even when crop quality is high, adverse post-production conditions in the garden center can eat away at profits. This article will discuss some common problems that may arise with spring crops and suggest ways to avoid or mitigate these problems.
Many of the nutritional problems in spring crops can be traced back to a poor fertilizer plan or a breakdown in the fertilizer delivery system. The fertilizer program, growing media, irrigation water and crops all need to be integrated for optimal results. Even though plants can be very forgiving, problems will occur if the nutritional program is lacking some essential elements, growing media pH is off or the correct amount of nutrients are not delivered when the crop needs them. Diagnosing these problems is best done by a lab with media and tissue testing, but there are some great visual diagnostic guides that can be helpful in a pinch, as well as on-site EC and pH readings.
Common problems that arise in the area include:
Problem 1: Yellow, stunted plants due to low fertilizer concentrations or infrequent applications
- Some growers try to get too much out of the lean nutrient charge added in the growing media by the soil blender. This charge is not designed to grow a crop long-term. A regular feed program is needed in this case.
- Prolonged cool, cloudy weather will stunt plants, especially if pots are sitting on the ground. When growers can’t irrigate because the soil is too wet, there is no good way to deliver water-soluble fertilizer.
- Some growers clear-water leach periodically, resulting in the loss of nutrients from the root zone. Only use clear-water leaching in soilless media if soluble salts are excessive or if there is an accumulation of some harmful ion, like sodium.
- If a greenhouse only has one feed rate set for bedding plants, heavy-feeding crops may be getting an inadequate diet.
- If there is green bark or poorly aged bark in the growing media, nutrients can be robbed from the crop–even if the fertilizer rates or concentrations are correct.
- Containers located under benches or hanging baskets may receive frequent leaching from the containers that are overhead.
- Broken injectors, clogged emitters, inaccurate dilution or measuring of fertilizer may also contribute to this problem.
Solution: Check injectors and stock tank solution using an EC meter and correct any errors. Assess soluble salts in the root zone using a 2:1 or pour-through. Temporarily increase your water soluble concentration for a few irrigations until you build up nutrient reserves. Plants should respond to higher feed rates in a few days if this is the cause of the observed symptoms. Once the system is balanced, reduce fertilizer concentrations and continue with constant fertilization at the appropriate level.
Problem 2: Burnt roots, stunted plants due to high soluble salts
- Soil containing controlled-release fertilizers should be used as soon as possible after blending since the fertilizer begins to release at this point. If the rate is too high or inconsistent, or if the mix is stored for too long a time (especially at a high temperature), soluble salts can build up to extremely high levels.
- Some growing media components, like coconut coir pith, may contain high levels of potassium, sodium or chlorides. These levels should be carefully monitored.
- If a greenhouse only has one feed rate set for heavy feeders, light feeding crops may be getting too much fertilizer.
- Irrigation water may contain high levels of sodium or chlorides. This can occur especially with shallow ponds near roads. If rock salt is used on the roads, spring run-off can elevate the level of these harmful ions.
- Broken injectors, inaccurate dilution or measuring of fertilizer may also contribute to this problem.
Solution: Water treatment (reverse osmosis/ filters) may be necessary if the irrigation water contains high levels of harmful salts. Check injectors and stock tank solution using an EC meter to make sure water-soluble fertilizer application is correct. Assess soluble salts in the root zone using a 2:1 or pour-through. Clear-water leaches may be appropriate for a few times to bring salt levels down. If salt levels are extremely high, sometimes a sugar solution (1 lb/100 gal) will provide temporary relief. Once the system is balanced, apply the required concentration on a constant basis.
Problem 3: Growing media pH out of balance
- Growing media pH impacts nutrient uptake and utilization. Root zone pH can rise or fall too much because of a number of factors.
- Growing media companies monitor their raw materials and apply limestone to adjust the initial root zone pH. The impact of this lime change is temporary, and that’s when the fertilizer type/concentration and water quality need to take over, determining long-term root zone pH.
- If the fertilizer is not fitted to the irrigation water (if the fertilizer is too potentially basic or acidic for the specific crops and water quality), growing media pH can plunge or skyrocket, leading to micronutrient deficiencies or toxicity symptoms. Unfortunately, within the multitude of spring crops, there are plants that have sensitivity to both conditions
- Micronutrient-sensitive plants can exhibit toxicity symptoms when growing media pH falls below 5.8. This is manifested by yellow splotches on lower leaf margins that can progress to leaf dead margins.
- Plants with a higher micronutrient demand will lose color on new growth as the root zone pH rises above 6.0 to 6.5. This will lead to stunting, yellow leaves and overall poor growth habit.
Solution: Discuss your crop needs with your soil mix company and fertilizer manufacturer. Mixes can be made with higher or lower lime charges that can help with root zone pH management. In crisis mode, additional micronutrients can be sprayed or drenched, acidifying fertilizers (or mineral acids) can be employed or basifying fertilizers (or bicarbonates or liquid lime) can be used to either treat the symptoms or correct the pH balance. The best approach, however, is to select the proper fertilizer based on irrigation water quality (primarily bicarbonate levels) before the spring starts, avoiding these problems altogether.