Quick Tips for Fertilizing Fruit Crops in the Fall

 

Photo: A Regent apple tree in the fall. AK.

Author: Annie Klodd, Extension Educator - Fruit and Vegetable Production

For many, fall is a convenient opportunity to do soil testing and apply certain fertilizers. Be careful about what and when you are applying in order to avoid problems going into winter.

Fall is a great time to amend the soil pH if it is too high or low. Refer to this article for information on lowering soil pH in fruit and vegetable crops.

As a general rule, it is safe to apply fertilizer and pH amendments to fruit crops in the fall, with the exception of nitrogen. Most nitrogen sources should be avoided in the fall, as they can stimulate unwanted new plant growth if applied before the plants are dormant, and can leach out of the soil with snow and rain before the next growing season. The exception is nitrogen-rich compost and composted manure, which can be safely applied once the soil temperatures dip below 50 degrees F. 

Some growers report that they find it difficult to source fertilizers that contain no nitrogen. If this is the case for you, I recommend waiting until the spring to fertilize. However, there are many fertilizers available that contain no nitrogen. Examples of nitrogen-free phosphorus and potassium sources include: Rock phosphate, superphosphate, triple superphosphate, potassium chloride, potassium-magnesium sulfate, and potassium sulfate. Ask your chemical supplier about product options and whether they do custom mixing.

Deciding what to apply:

As always, apply fertilizers and pH amendments based on soil and foliar testing results. In most cases for fruit crops, soil fertilizer is meant to be applied on a prescriptive basis (apples are a bit of an exception, as they need annual maintenance fertilizer, see below). While applying the same mix of nutrients each year may seem easier in the moment, this practice can lead to toxic buildup of certain nutrients and increase costs without adding any benefit. If fertilizer decisions create stress, try to plan ahead and seek help from an Extension Educator or chemical supplier with professional training in nutrient management. See this webpage for more information.

A quick tip on soil testing:

Submit several samples per field or high tunnel to get a more precise picture of soil fertility throughout the field. By doing this, you may learn that some pockets of your field have different nutrient needs than others, so you can treat them accordingly while saving money on others. Read about grid sampling and directed sampling here.

Other considerations by fruit crop:

Apples:  

Apples are sensitive to nutrition, and many apple Extension specialists do recommend annual maintenance fertilizer application to make up for nutrient losses through fruit and fallen leaves. However most of this occurs earlier in the season. Apple trees use high levels of nitrogen and other nutrients early in the season and during fruit development, and use significantly less in the late season. 

Urea is sometimes applied in the fall to help break down fallen leaves, as part of an apple scab management program. Source.

In a maintenance program, most fertilizer is either soil- or foliar-applied between green tip and early cover sprays. After harvest, the UMass apple program recommends maintenance potassium and corrective nutrients if needed, plus as-needed corrective lime or sulfur for soil pH. This is an excellent resource! See pages 104-105.

Grapes:  

Fertilizer recommendations for cold climate grapes are well-established and based on research performed on Minnesota vineyards. Please read about these recommendations in Tissue and Soil Nutrient Testing for Cold Climate Grapes and Applying Fertilizer to Vineyards After Harvest. 

Fertilizer is most often applied in the spring, but prescriptive fall applications can be beneficial to fix nutrient deficiencies as long as they do not contain nitrogen. In fact, we often fight against excessive vine vigor in grapes, so I would argue that it does not make sense to apply supplemental nitrogen in this crop unless foliar tests or consistently low vigor indicate a problem. 

Avoid the temptation to apply pre-set annual fertilizer mixes. Instead, only apply fertilizer if needed and calculate the rates and nutrient ratios based on soil and foliar test results. For help, you can contact your local Extension Educator or find a chemical representative who is well-trained in this field.

Raspberries: 

 As with other fruit crops, use the time after harvest ends to evaluate the health of the raspberry patch and take soil samples for testing. Soil samples should be taken every 3-5 years or when a nutritional problem is suspected. It is too late in the season to do foliar testing. Direct fertilizer into the rows using a targeted spreader, avoiding fertilizing the aisles. In high tunnels, most fertilizer should be applied with fertigation because soil-applied fertilizers are hard to incorporate in the absence of rainfall. Download Organic High Tunnel Raspberry Production.

Honeyberries: 

 

This crop has relatively low fertilizer requirements and can grow in a wide range of soil pH (5-7). Published recommendations from the honeyberry research group at University of Saskatchewan say to only apply fertilizer in the spring on an as-needed basis. Later-season applications are a poor practice because they cause unwanted late-season growth that decreases winter hardiness. They also report that 1) Most midwestern soils have sufficient nutrition to support honeyberries so supplemental fertilizer is often unnecessary unless problems are observed, and 2) soil testing laboratories are very unlikely to be able to interpret test results for this crop specifically - it is a minor crop with minimal research-based fertility information available. https://research-groups.usask.ca/fruit/documents/haskap/growinghaskapinCanada.pdf

 

June-bearing strawberries: 

 

June-bearing strawberries need to go into the winter with strong nutrient reserves in their roots, so they can grow rapidly in the spring and have high yields. This doesn't necessarily translate into heavy fall fertilization, as most fertilizer is applied pre-planting and at renovation. But fall is a fine time to apply phosphorus and potassium particularly if a soil or foliar test indicates a deficiency. If adequate P and K were applied prior to planting, you might not need to apply any more until the next planting. To reduce cultivation passes, many growers may find it easier to apply P and K during renovation rather than the fall. In terms of nitrogen, in Minnesota we recommend making the final nitrogen application during renovation in July. Read Strawberry Nutrient Management (UMN Extension) and Strawberry Nutrient Management Guide for Oregon and Washington for more information.