January 2014 Issue 6

In this issue:

1) Garden Planning Tips
2) Soil Science Lesson: Cation Exchange Capacity: Part 2

Garden Planning Tips

Even though the first ripe tomato is probably 7 months away, I start drooling with anticipation. The time for planning the garden has arrived!

Here are some planning tips to keep in mind as you leaf through the catalogs:

1. Grow plenty of your proven, standby favorites, and then choose two or three new things to try from the seed catalogs. As well as trying out a new variety or two, try out a whole new vegetable you’ve never grown before.
2. Have your garden layout from last year in hand, and practice good crop rotation.

   Try not to plant the same kinds of plants in the same place they grew last year. In fact, it’s best to avoid planting the same thing in the same place for at least three years, to avoid soil borne plant diseases, nematodes, over-extraction of plant-specific nutrients, etc.

   Plant tall things (like pole beans or corn) on the south side of plants that appreciate some shade during the heat of summer, such as lettuces or collards (if you’re in the southern hemisphere, the north side.)

3. Leave some empty spaces to allow for succession planting of fast maturing crops like radishes or lettuce.
4. Try growing the “Three Sisters” in one part of your garden: corn, pole beans, and squash, all in close proximity. The corn gives the beans something to climb up, the beans give the corn a bit of the nitrogen they crave, and the squash shades the ground to minimize evaporation.

Soil Science Lesson: Cation Exchange Capacity: Part 2

CEC is an indication of how much cation plant nutrition your soil can hold (similar to having cubbyholes in a pantry). A loose soil like sand has very few of these “cubbyholes” and is not be able to hold much plant nutrition, whereas a loam soil which contains a little clay may be able to hold a lot. The more your soil can hold (the higher the CEC), the more resistant it is to losing plant nutrition by it washing away, or “leaching”, and the more fertile it can be.

Sandy soils may have a CEC of only 3-5, silty loams a CEC of 10-25, clay loams a CEC of 30-40, and organic "muck" soils a CEC of 50-100.

If you have low CEC soil (3-5), you can increase the CEC by adding lots of completely-broken down, well-balanced compost, or you can boost it even more by taking a tiny bit of clay dug up from the subsoil (or taken from an exposed road cut), pulverizing it and mixing in with the compost you add.

With a low CEC soil you will also need to fertilize more often, because the fertilizer will wash away more quickly. If your CEC is above 10, annual fertilization should be sufficient.

Base Saturation: Calcium, Magnesium and Their Friends

Roughly speaking, the total cation plant nutrition a soil actually does hold is referred to as “base saturation”, which is given on a soil test report as relative percentages of each of the cation nutrients. What does that mean?

Whether your soil holds a lot or a little, whatever that total CEC amount is can be seen as “100%”. On a soil test, the relative percentages of the various cation plant nutrients - namely calcium, magnesium, potassium, sodium (and a few others) - will add up to that 100% total.

Now from a plant’s perspective, the tastiest soils seem to have a ratio of about 68% calcium to 12% magnesium, or what some have called an “ideal soil”. For complicated reasons, when the calcium/magnesium ratio is right, the pH will be right, the soil microorganisms will be happy, and plants will be happy, provided they have enough of all the other macro and micro nutrients.

Most of us tend to think only of Nitrogen, Phosphorus and Potassium, or N-P-K when we think of fertilizer. They are the biggies, but for optimal soil health, we also need to consider the presence of calcium and magnesium in the right ratio.

I encourage everyone to have their soil tested and optimize their soil minerals, so they can grow the most nutrient-dense food possible. Healthy, balanced soil also means fewer bugs!

Happy garden planning!