Managing Nutrition In Spring Crops

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The spring season presents some unique challenges for even the best growers. It can be a time of rapidly changing environmental conditions – some beyond the grower’s control – that may negatively impact crop quality. Often, growers plan multiple crop turns to meet desired shipping dates that are subject to last minute shifts due to fluctuating weather and market conditions. Plus, there are hundreds of different spring crops available, making even more it difficult to stay on top of their various nutritional needs. To further complicate matters, this enormous list of spring crops continues to expand every day.

Managing the nutrition of spring crops can be compared to running a diner with a gigantic menu that includes various eclectic offerings from Italian to Chinese. I’ve often wondered how the cooks in those establishments are able to efficiently supply such a wide variety of meals on demand at a relatively low cost. I can only surmise that it comes down to keeping a few basic ingredients on hand that can be quickly combined into a wide variety of meals. Likewise, today’s growers must efficiently and economically satisfy the cravings of multiple spring crops with very diverse nutritional demands. Combine this with the overall hustle and bustle of the spring growing season, and you’re faced with a situation that can make devising the perfect fertilizer program very difficult.

In the same growing environment, some or all of the following crop types with vastly different and sometimes conflicting nutritional needs may be present:

• Bedding plants that will only be grown for the few weeks it takes to gain size after transplant from the plug stage. Generally, these plants will have low nutritional demands to maintain a compact size during the shipping and retailing phase.

• Crops with heavier nutritional demands that are typically produced in hanging baskets, such as geraniums and vegetative crops.

• Crops favoring lower-growing media pHs with higher iron or other micronutrient demand, like vegetative petunias or calibrachoa sp.

• Crops that prefer higher-growing media pHs, with sensitivities to excess iron or other micronutrients, like seed geraniums and marigolds.

• New crop types where little is known about nutritional requirements.

• Combination planters that contain a variety of plant types based on aesthetics, not nutritional requirements.

Additionally, overhead growing space may be taken up by numerous hanging baskets, and other crops may be randomly placed underneath them or scattered around the greenhouse wherever there is available growing space. In all this confusion, remember the challenge of the short-order cook. By simplifying ingredients and planning efficient systems ahead of time, growers can design better fertilizer programs for their spring crops. Following are a few tips to make your nutritional program as easy and effective as possible, so you can focus on growing high quality crops: 

Nutrient Monitoring

Do your homework before growing the crop to avoid many commonly occurring problems.

• Test all water sources ahead of time so you can select the correct fertilizer(s). Irrigation water may be limited or you may have to use multiple water sources. You may need to acidify your water before applying it to crops.

• Do research on crop nutrient needs with university researchers, Extension agents and suppliers of plants, growing media and fertilizers.

• Match your water-soluble fertilizer formulation to the buffering capacity of the water (total alkalinity or bicarbonate levels), and add any essential elements not provided by the water or growing media (e.g. calcium or magnesium) at the correct levels and ratios.

• Use free tools from the experts. The Scotts Company offers a new patent-pending Peters A-B-C Selection System online (www.petersabc.com) to help growers determine their best nutrition options based on water quality and crop.

• Regardless of the fertilizer(s) you select, monitor the growing media frequently on site, and take corrective action prior to the onset of symptoms. Labs can help you monitor the comprehensive growing media, and plant tissue testing may help you diagnose nutritional problems. 

Fertilizers

If you are growing a variety of crops, settle on a general feed program and prescriptively treat plant types with special nutritional needs.

• Don’t try to save money by skimping on fertilizer concentrations. Inadequate feed levels often result in uneven growth and increased production time. A good place to start is by using 100-150 ppm N as a constant liquid feed. If zoned, you can nourish heavier-feeding crops at higher concentrations or supplement them with controlled release fertilizers (CRFs).

• Avoid fertilizers with excessive ammoniacal (NH4) or urea nitrogen in conditions where conversion to nitrates is slow (e.g. cool soils).

• Avoid excessive phosphorous (P). Reduce plant stretch by choosing fertilizers with P levels 1⁄3 to 1⁄5 the level of the nitrogen, especially in fertilizer programs that use phosphoric acid for acidification. For example, consider trying Peters Excel 21-5-20, 13-2-13 or Peters 17-3-17, 15-5-15, 15-2-20 instead of 20-10-20, 15-15-15 or 20-20-20. It doesn’t make sense to encourage excess growth with fertilizer and then counteract that growth with the use of PGRs to keep plants compact.

• Address crops that require lower pH levels (like pansies or petunias) with lower lime rates in growing media or use more acidifying fertilizers and/or inject acid if possible. Periodic drenches with Peters 21-7-7 or STEM can "green up" these plants when root zone pHs become too high.

• Use basic fertilizers such as 13-2-13 and 15-2-20 or work 15-0-15 into your rotation. Include higher levels of lime in the growing media and/or reduce the level of trace elements to avoid micronutrient toxicity syndrome on iron sensitive crops such as geraniums (zonal and seedling) and marigolds.

• Supplement heavy-feeding crops like vegetatively propagated petunias, calibrachoa, geraniums, foliage, mums and hanging baskets with a low rate CRF like Osmocote Plus 15-9-12. The CRF provides a base feed for those situations when you can’t use water soluble fertilizers – such as during cool, cloudy weather or during busy shipping times – and continues fertilizing the crop after purchase by the garden center or homeowner. With supplemental CRF, you can maintain better foliage color due to constant, uniform feeding throughout the crop cycle without having to change your general water-soluble program. Remember, crops that spend time outdoors are subject to leaching rains, and a low level of CRF can insure a base level of feed.

• Zone crop types where practical to make prescriptive treatments of iron chelate, etc. possible.

Careful fertilizer selection coupled with measuring and monitoring nutrient status in your water and growing media will help you successfully grow quality spring crops.

Fred Hulme, Ph.D. is Director of Technical Services at Everris.

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