Fall Garden Soil Preparation Tips

Fall Garden Soil Prep Tips

By Richard Godke

Fall is the best time to prepare your garden soil for next spring.  Soil is the most important factor in raising a successful garden.  There are five basic fall soil preparation components that you will need to explore to maximize soil fertility.  These components are: soil pH; soil structure; and the levels of  phosphorus and potassium, secondary and micro nutrients, and nitrogen.  New gardeners will not want to mess with soil preparation.  Purchasing bagged garden soil is simple and easy.  The bagged soil has been tested, nutrients added, and is properly mixed to give you what you need to get started.  I would recommend checking out http://homegardeningforbeginners.org/featured/bag-gardening-for-home-vegetables/ which explains a great way to easily grow vegetables right in the soil bags.

Fall Vegetable Garden Soil Test

Fall is the best time to annually test your soil so you can adjust the pH, phosphorus, and potassium.  Check with your County Extension Office http://npic.orst.edu/pest/countyext.htm for places to have your soil tested.  Many Extension Office test soil samples for pH levels for free.  Most offices can send samples to their affiliated university for pH, phosphorus, potassium and other tests for a fee.  This office recommends soil additives and application rates to correct any problems specific to your soil samples and soil in your area.   To take a soil sample get an equal slice of soil at least 8” deep for every 100 square feet.  Keep surface debris out of the sample.  Place the samples in a bucket with up to five other spade slices., mix all samples together well, and take about two cups out for each sample.  Record on the sample label your name, date and sample number.  Make a diagram map that shows where the sample came from.  Let the samples air dry to prevent soil fertility changes.  You can purchase a home test kit and meters that you can test for pH, nitrogen (N), phosphorus (P), and potassium (K).  I have not had very consistent results from these home tests.

Fall Garden Tips for pH

The pH is the most important single soil component.  pH is the scale is from 1 to 14 that measures the levels of acid or alkaline in the soil.  Most garden plants prefer the pH between 5.5 and 6.5.  Lime is used to raise the pH and sulfur is commonly used to lower the pH.  If the pH is too high or low it can tie up many needed plant nutrients.  It is important to make the recommended additions in the fall before deep tilling.  The soil pH is not mobile in the soil.  For example, if limestone is applied to the surface without tilling, pH will be very alkaline on the surface and very acid deep in the soil.  It takes time for the additives to change the pH of the soil so it is ideal to apply lime or sulfur in the fall.  The smaller the lime is ground up the quicker it will change the pH.  Soil pH is the most important component when preparing you fall garden and will correct most deficiencies of micronutrients.

Phosphorus and Potassium Suggestions for Fall Garden

Phosphorus and potassium are two macro-nutrients that are needed by plants in relatively large quantities.  A fall soil test is the best way to determine the level of these two elements.  These elements are not very mobile in the soil like the pH additives.  They need to be tilled into the soil at a depth of 8”.  Your Extension office can recommend the amounts of phosphorus P?O? and potassium K?O for you soil types.  Phosphorus deficiency results in slow growth and older leaves turn purple.  Potassium deficiency results in slow growth and leaf edges turn light green to yellow.  Fertilizer labels have 3 numbers, the N-P-K formula, for example: 10-5-15. These numbers represent 10% nitrogen, 5% phosphorus, and 15% potassium per bag. The remaining 70% consists of fillers.

Fall Garden Soil Structure Information

Soil structure refers mainly to the size of soil particles.  Soil has three size categories: clay –small, silt-medium, and sand-large.  Which is best?  Each size has advantages and disadvantages.    Clay for example will hold nutrients and moisture but it is so dense the plant has a hard time sending roots through the tight mass.  Sand has plenty of air pockets for the plant roots but does not hold nutrients, and the soil dries out quickly putting plants at a disadvantage when it is dry.  A combination of different sizes is the best.  Adding organic material to any of these soils is what I recommend.  Compost, coconut coir, large animal well-rotted manures and peat moss will provide needed plant nutrients, hold water and allow good air movement in the soil.  I had a garden with some of the best soil in the world that was 6 feet of top soil and I still had a big increase in yields as a result of adding compost.  Adding organic materials to your fall garden will help correct any problems you soil structure might be causing.

Fall Garden Plan for Secondary and Micro Nutrients

Secondary nutrients include: calcium, magnesium, sodium, and sulfur.  They are required in small quantities but are still essential for good plant growth.  Plant micronutrients are elements needed in even small amounts than the secondary groups for the plant to thrive.  They include manganese, boron, copper, iron, chlorine, molybdenum, and zinc.  Soils with high amounts of organic material and have a soil pH between 6 and 7 tend to have adequate amounts of these elements.  In most cases testing for micronutrients is not needed unless the plants are not productive.  To insure you have enough organic material spread 25 to 100 pounds of compost or partially decomposed manure per 100 square feet.

Nitrogen Advice for Fall Garden

Testing for nitrogen is not recommended.  Nitrogen is very mobile in the soil.  Excessive snow melt, rain and irrigation can move the available forms of nitrogen below the root zone.  For the most eco-friendly application of nitrogen, fertilize in small amounts and increase amounts when the plant is rapidly growing.  For example a corn plant uses the largest percent of total nitrogen between being knee high and tasseling.  Here is a good video on “Planting a Vegetable Garden for Spring” http://www.youtube.com/watch?v=gNOe0UogfY0&feature=youtu.be.  My rule of thumb is to fertilize with nitrogen when the plant loses its deep green color and the growth slows.  Too much nitrogen will cause green plant growth and suppress fruit formation.  Adding too much fertilizer is a problem many beginning gardeners make

Fall is an excellent time to prepare your garden for next spring.  Soil preparation requires soil testing and an adjustment period for the soil.  If pH additives and additional phosphorus and potassium are needed it all must be incorporated 8” deep to maximize the results.  Tilled in compost or animal manure in the fall helps build beneficial soil organisms (bacteria, fungi, and worms) during the winter months.  Here is some excellent information on “Fertilizing the Organic Garden” http://extension.unh.edu/resources/files/Resource000489_Rep511.pdf.  By understanding and preparing the soil you will maximize the production of your spring garden.  Many gardeners wait until a later convenient time and that results in this gardening task not getting done.  Start your spring garden with the proper fall garden soil preparation.