Sunflower Soil Prep and Fertilizing

Sunflowers prefer well-drained, fertile soil with some clay loam content; these heavy feeders require rich nutrients in order to flourish tall and healthy.

Every gardener encounters challenges like compaction, drainage issues and nutrient deficiency; over time they learn how to resolve these problems. If you want the best sunflower results possible, follow these guidelines for soil preparation and fertilizing.

Soil Preparation

Sunflowers require excellent soil drainage and balanced fertilization to thrive, and prefer medium to coarse textured soil that is neither too stony or clayey. Their ideal environments are open areas free of weeds with adequate sunlight (6-8 hours daily). When planting sunflowers outdoors it is wise to locate them somewhere protected from wind; otherwise their top-heaviness could result in blowover. Specimen cultivars of giant sunflowers may need support as some varieties require staking.

Nuseed sales representatives can be an invaluable source for hybrid selection and advice. They know all of the hybrids they carry as well as which markets and regions in which sunflowers will perform best.

Pre-plant soil tests can help determine the appropriate amounts of nitrogen (N) and potash (K2O) required to achieve maximum yield, and establish pH. Test results provide valuable insight into this vitally important aspect.

Enhance the soil with organic matter such as compost, manure or sorghum in either spring or fall; or apply commercial fertilizers four to six weeks prior to planting sunflowers. Sunflowers require plenty of nitrogen for vigorous growth and seed production as well as plenty of potash and phosphorus to promote healthy leaves and large flower heads.

Sunflowers typically benefit from receiving 15N/acre as their extensive roots can efficiently use residual nutrients, so fertilizer application usually is not as crucial.

Fertilizing

Sunflowers are heavy feeders and require ample soil nutrients. Prior to planting, soil samples should be taken in order to assess their availability, and help choose an adequate fertilizer rate for their sunflower crop.

Sunflower seeds respond well to nitrogen (N) fertilizers, yet too much N can cause excessive vegetative growth, increased disease incidence and delay maturation, leading to decreased seed oil content and quality.

Soil pH affects the availability of macro and micronutrients, with acidic soil being less capable of holding and using these essential resources than alkaline soil. Lime can help lower acidity of soil to help it retain and deliver more effectively its nutrients.

Planting in rich, well-draining soil is key to successful plant emergence and stand establishment. A good seedbed preparation, whether conventional-till or no-till, must also take place to avoid compaction that might prevent germination and result in uneven stands.

An effective fungicide program is essential to sunflower production. Applying fungicide at planting or using seed treatments such as Gramoxone Super to protect sunflowers against stalk rot caused by Sclerotium bataticola can protect them against this fungal pathogen, especially under warm and drizzly conditions. To combat it, Gramoxone Super can be applied directly onto fields.

Watering

Sunflowers can grow successfully in many different soil types, though optimal performance comes when growing them on well-draining ground. If soil becomes dense or tends to clump together, adding amendments such as sand or compost four to six weeks prior to planting may increase yields and help improve productivity.

Young seedlings need to be watered daily in order to prevent wilting; mature plants require deep irrigation about once or twice weekly in order for their roots to access moisture deeper within the soil. Avoid watering sunflowers during hot weather to avoid leaf scorch.

Balanced fertilization is key to maintaining the vitality of mature sunflowers. You may use either liquid fertilizers at seedling stage, or add organic granular fertilizers at time of planting, for even germination and plant stand establishment. A low nitrogen content is recommended; too much nitrogen encourages large leaves with few flowers.

Keep a close eye on your sunflowers to monitor for fungal diseases, such as downy mildew, rust and sclerotinia mold. If any are detected, spray with general garden fungicide to control disease spread. A three-year crop rotation plan is advised in order to decrease disease and weed pressure while rotating sunflowers with legumes or other nitrogen fixing crops can help maintain healthier soil between growing seasons.

Weed Control

Sunflowers perform well in most soil conditions, but their yields tend to be highest when grown on well-draining and fertile land. Compaction, poor drainage, or nutrient deficiencies will impede sunflower development; loosen compacted soil using aeration tools or amend deficient fields with organic matter for increased crop health and higher yields.

Sunflower seedlings are highly susceptible to competition from weeds, making early season weed control essential for their success. Soil-applied preemergence herbicides are essential in reducing weed pressure and helping your crop establish itself before competition sets in. Furthermore, traditional sunflower varieties offer limited postemergence options for broadleaf weed control which makes an effective preemergence program even more important.

Planting into a clean, uniform seedbed will increase germination and emergence in sunflower. No matter if using conventional or no-till planting techniques, having a firm surface on which you place the seeds will help minimize soil drift and ensure even placement of seeds.

Farmers must consider whether sclerotia exists in their soil before planting sunflower. The disease tends to thrive on recently tilled or disked land; growers can reduce its likelihood by rotating sunflower with crops less vulnerable to this affliction.

Realistic yield goals must be set, with fertilization adjusted accordingly depending on geography, soil type and expected precipitation. Soil testing should also be used as a way of providing specific recommendations that will help reach these targets.