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News for Norther Colorado and the world

Sunday, November 18, 2018

Gardening Q&A: Pay Attention to Soil Amendments

By Kathy Roth
CSU Master Gardener in Larimer County

Q: What are my choices for soil amendments and what are their differences? Which one should I use?
A: Organic amendments include sphagnum peat moss, wood chips, grass clippings, straw, compost, manure, biosolids, sawdust and wood ash.  Inorganic amendments include vermiculite, perlite, tire chunks, pea gravel and sand. Not all of the above are recommended by CSU; some can cause problems. Wood ash, for example, is high in both pH and salt. It can intensify common Colorado soil problems and should not be used as a soil amendment. Don’t add sand to clay soil — this creates a soil structure similar to concrete. 

A full discussion of choices (and their pros/cons) is detailed in CSU Extension Fact Sheet 7.235, found at www.ext.colostate.edu. Remember, plants and vegetables will only be as healthy as the soil in which they’re grown! “About 80 percent of plant problems are caused by bad soil,” says Carol O’Meara, who is the Horticulture Entomology Agent for CSU Extension in Boulder County.

Q: If I’m careful and cover my plants on cold nights, can I go ahead and plant warm season crops, like tomatoes, earlier than mid-May?
A: Not only frosty nights, but soil temperature and daytime temperatures help determine optimal planting times. Warm season vegetables require daytime temperatures above 60 degrees F, but prefer summer-like temperatures between 70 and 95 degrees F.
 
Warm season plants can be sensitive to cool spring winds, which still occur in May. In short, it isn’t only cold nights you need to protect these tender vegetables from.
 
A common problem found in tomatoes planted too early is blossom end rot, which can be caused by cold temperatures during blossom set (or by very hot temperatures later in the summer or uneven watering). Some gardeners successfully utilize commercial products in which circular water-filled bladders help trap warm daytime temperatures and radiate the heat through our chilly nights. This helps prevent extreme fluctuations in temperatures directly around small, new tomato plants. Other gardeners recycle 2-liter soda bottles filled with water and set them in a circle around new plants to achieve the same goal.

Q: What is the deadline by which I should have my garden entirely planted?
A: The practice of “Succession Planting”, continuous plantings of small quantities (not planting the entire seed packet at once!) sowed two weeks apart, ensure a steady harvest over long periods of time. This is preferable to many, instead of harvesting one giant bumper crop that you have to can, freeze or give away to your neighbors. A detailed planting guide on vegetables for our area can be found on CSU Extension’s Garden Notes #720, found at www.cmg.colostate.edu, along with the tip that, “In the warmer areas of Colorado, cole crops (cabbage, cauliflower, broccoli, and Brussels sprouts) produce the best quality when direct seeded mid-summer (early July for the Front Range area) for harvest during cooler fall weather.”

Q: Once my seedlings emerge from the soil, how soon do I begin to fertilize?
A: CSU Extension Fact Sheet #7.611 discusses fertilizing vegetables, but warns that “The amount and type of fertilizer for vegetables should be based on a soil test,” conducted by an analytical laboratory. CSU Extension Garden Notes #221 explains available soil tests, methods and how to correctly take the soil samples.  The information cautions the use of home soil test kits. “The actual process used on some procedures is based on soil pH. Most home test kits were designed for acid soils, and would have questionable accuracy on the alkaline soils of the west.” Fertilizer nutrients required by vegetables in the highest quantity are nitrogen (N), phosphorus (P) and potassium (K). Excessive amounts of nitrogen can reduce production and quality, and increase insect and disease problems. Applying phosphorus when not needed can increase chlorosis. Truly, soil testing is needed!


The author has received training through Colorado State University Extension’s Master Gardener program and is a Master Gardener volunteer for Larimer County.

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