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Community Corner

The Soil Needs Food Too, But Not Until the Temperature is Right

Here are some ideas about the science of soil health and how to give your soil the food it needs.

Alison, I'm pretty sure I need to add some fertilizer to the funky Benicia clay soil in my yard.  Do you have any suggestions?  Do I need to adjust the fertilizer for the plants?  Should I the fertilizer in soon?

Well, don’t do much right now. First, it is (thankfully) raining and cold.  The cold impedes the ability of plants to utilize nitrogen so not much is going to change for a while.   Second, you need to know a bit about the dirt in your yard so you can plan your strategy.  Read on for the whole answer.

In a perfect world, planting is not done on a whim and with little planning.  In a prefect world, a garden is planned and zoned so that plants with similar needs are grouped together and soil tests are done so that the area can be manipulated to achieve the highest quality soil texture and fertility for the plants in that area.

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In reality, the way planting usually works is more likely inspired and impulsive.  You see a cool plant in the nursery and it is calling your name (yes your name) so loudly that you can’t get out of the door without dropping 5, 10 or even 100 dollars on it.  You get home and say to the inspiration… “now what?”.   This is where the science is lost on just about every human.  If you have a nice low water native garden and your new plant is of the same need, this is great.  Go right ahead and plug that plant into the group.  The reality is that if you have a nice low water native garden, the new acquisition is likely to be different than what you have (sorry, variety is the spice of life).  So what do you do?

Short of handcuffing your self or avoiding the places where plants are sold, plan to have a few different zones in your garden.  In my less than perfect world, we have a couple of hot hill zones, a sunny flat area and a semi-shady flat area.  The hills are ideal for local natives like Manzanita and Ceanothus, with a few terraces; we are able to keep a few fruit trees up there too.  In the back there is a flat sunny area, which is shared by a lawn (for the tortoises) and a veggie garden (for the humans). The flat semi shade area is where I am going crazy with mounds and stuff; check back in a year or so to see how that is working for me. 

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Now let’s look at the soil stuff.

Plants that do well in river valleys and deciduous forests will thrive in areas with low ph soils and plenty of organic material.  The local natives that thrive perched on a hillside will do just fine on a slope with a higher ph, sand and clay soils.  So what is a person to do? 

When you begin to make decisions about what direction to go with your garden, it is a good idea to have your soil tested.  This is not cheap, especially if you have a few different planting areas.  A lab test runs $30.00 to $50.00 for each sample tested.  If you like to play with test tubes and pipettes, you can get a good soil test kit by LaMott for about $60.00, which will provide you with about 15 tests.  There is a kit by Rapitest available at Pedrotti Ace Hardware (in Benicia California) that is 10 tests for about $18.00.  Be sure to pick up the distilled water for the test while you are there, another $4.00.  Both tests delivered similar results in a control study, at my little scientist’s lab.  The LaMott kit is way cooler-I felt like I was back in the real world of science while I used it!  How ever you choose to test your soil, it is a good thing to do.

I have performed a few soil tests over the years in Benicia.  What I have found is that our scraped surfaces (think housing tracts) have almost no nutrient value and the soils are slightly to moderately alkaline.  Up the hill on any scraped slope, there is a sandstone base rock and the top soil has a strong clay constituency.  That is the soil texture.  Soil texture can be changed, but it takes a bit of work. 

When creating a new garden, there are those who import substantial amounts of topsoil when redoing a landscape.  Others just let the soil be.  Then there is the middle ground, creating a healthy soil.  The Bay Friendly Coalition has some good literature about building healthy soils.  We are luckey to have one of the best suppliers of organic compost in the Bay Area, Organic Solutions, located on Goodyear Road, near Lake Herman Road.

 OK, back on topic here.  Say you tested your soil and found it wanting.  You have been reading the Bay Friendly literature and you think that you need to top dress the planting area with compost (good idea) and maybe add an organic fertilizer (also good thinkin’).  There are a few little tips to keep in mind. 

  • Nitrogen will not be utilized by plants when the soil is less than about 50 degrees or over about 75 degrees.  So fertilizing in the spring or fall is best.  Under 50 and the nitrogen is washed into the bay, over 75 and it can be denitrified into the atmosphere.  See more about nitrogen loss here.
  • Phosphorus and potassium will build up in the soil.  Older gardens can have high concentrations of each.
  • Plants tend to do best in gardens where the soil is most like their native environments.
  • N P K and their numbers are listed in that order on fertilizers. 16-8-10 would be 10 percent Nitrogen, 8 percent Phosphorus and 10 percent Potassium.  Need more, try this link.
  • NPK are just the top players.  There are macro and micronutrients that are important too.  Many of these will enhance the effectiveness of any fertilizer. 
  • A soil that has had compost and organic fertilizers used will tend to support the proper chemical balance and soil structure for most plants.
  • Nitrogen encourages growth, Phosphorus encourages flowers and Potassium encourages healthy cell development.  None of these can be properly utilized without an appropriate Ph level and other nutrients being in balance.

 If I know the plants that need fertilizing, I can give a more specific answer, so drop a line any time!

Finally let me change the subject for a minute.  The Benicia Tree Foundation is planting trees at Joe Henderson Elementary School on Saturday January 28th from 9:00 am until about noon.  Come on down and have some fun planting with us!

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