Issue: January 2004

January Time to Prepare Soil for Spring Gardens

A good fertility program is the best way to prepare garden soil for spring planting, and winter is the time to begin the process. Having soil analyzed is the starting point.

Take soil samples at several locations in the garden to assess fertility levels. Take samples from six to eight inches deep, the depth most vegetable feeder roots reach.

Mix the soil thoroughly for a good, representative sample and send it to New Mexico State University's Soil, Water and Air Testing Laboratory in Las Cruces for analysis. (Contact your county Extension agent for information on where and how to send samples.)

Soil analysis results will be returned by mail and will include evaluations of soil texture, organic matter, pH, electrical conductivity, and amounts of nitrogen, phosphorus, potassium, magnesium, calcium and sodium in the soil. It will also include specific fertilizer recommendations for crops based on the soil analysis.

Soil texture refers to soil particle size. Lighter sandy soils have fewer nutrients and lower water holding capacities than heavier clay soils. Clay soil usually drains poorly. Silts fall in between sands and clays in terms of particle sizes. Loams are mixtures of sandy and clay soils.

Most unimproved soils in New Mexico are low in organic matter. Adding organic matter like compost will improve almost all soils. It will increase the water holding capacity of sandy soils and improve nutrient content. It will also improve drainage in clay soils.

Most New Mexico soils are either neutral or alkaline in soil reaction or pH. The higher the pH, the more alkaline the soil. Alkaline soils limit the phosphorus, iron and zinc available for plant uptake. To compensate, apply phosphorus in a band directly below the seed row. Apply iron and zinc to the soil as chelates to make them more available or as foliar applications to the plants.

Electrical conductivity measures the amount of soluble salts in soil. The higher the number, the more soluble salts. High levels can burn plant leaves.

Plants use nitrogen, phosphorus and potassium for optimum growth. Although a soil analysis usually reports the quantity of these nutrients in parts per million (ppm), most reports have a small bar graph explaining whether these figures are considered low or high. The report will recommend how much of these nutrients to apply for optimum production. It will include magnesium and calcium, but generally iron, zinc, and other minor elements will not appear in the report. Yearly compost applications will supply most of these nutrients to soil.

High sodium levels can block drainage. Adding gypsum or calcium sulfate to soil will often improve structure. During irrigation, calcium ions from gypsum replace sodium ions, causing soil particles to clump together and improve aeration and soil drainage.

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For more gardening information, visit New Mexico State University's Cooperative Extension Service publications world wide web site at

George W. Dickerson, Ph.D., is is a horticulturist with New Mexico State University's Cooperative Extension Service. New Mexico State University is an equal opportunity/affirmative action employer and educator.

Also Please join us on Southwest Yard & Garden, a weekly garden program made for gardeners in the Southwest on:
KNME-TV Albuquerque at 9:30 p.m. Saturdays,
KENW-TV Portales at 10 a.m. Saturdays,
and KRWG-TV Las Cruces at 11:30 a.m. Saturdays (repeated at 1 p.m. Thursdays.)