Herself’s Houston Garden

I bet you all know that you can ship off a pint of soil to be tested and the government will tell you all about it. I’ve known about it for years. I’ve even thought about doing it several times. But I never seemed to get there. This year I will be doing it.

If you go to Texas A&M University Soil, Water and Forage Testing Lab’s webpage you can get detailed instructions, a form to fill out and everything you need to do a soil sample. You can also go to your local extension office and pick up the form and a soil sample bag.

So why is this the best bargain for gardeners? It’s cheap, dirt cheap actually. For $10 they tell you your soil’s pH, Nitrogen, Phosphorus, Potassium, Calcium, Magnesium, Sodium, and Conductivity. For $15 they add in Zinc, Iron, Copper and Manganese, for $20 they check the organic matter also and for $25 they add in the Micro nutrients.

Soil testing will tell you exactly what you need to add to keep your plants thriving. So your plants thrive and you are not wasting money on chemicals you don’t need. Fertilizer is expensive. And probably you are using way more than you need. Unless it is a lawn, vegetable or other crop you take away there is likely plenty of most of what you need already in the soil.

The most important part for you is to get a good sample. You want to grab about 10 soil samples. Fetch some from each bed. Samples should be about 1″ across and 6″ deep. Just put your shovel in and grab a 6″ clod of soil. Then just grab the middle column.

Put all your samples in a clean plastic bucket. Mix well. Then fill the soil bag with the mixture and ship it off with your form and a check.

I mailed the test out Jan. 19th and received the results Feb. 2. Amazing, it is a wonder any thing is alive and no wonder I wasn’t getting any tomatoes. Here’s the results:

Analysis	Results	Critical Level	ExtLow, VLow, Low, Mod, High, VHigh, Excess	Recommendation
pH	8.0	6.5	Mod. Alkaline
Conductivity	181	-	None
Nitrate	3	-	ExtLow	1.3 lbs N/1,000 sqft
Phosphorus	34	50	Moderate Need	1.2 lbs P2O5/1,000 sqft
Potassium	80	175	Low	2.1 lbs K2O/1,000 sqft
Calcium	3349	180	High
Magnesium	131	50	High
Sulfur	24	13	High
Sodium	298	-	Low
Iron	27.06	4.25	High
Zinc	3.54	.27	High
Manganese	7.9	1.00	High
Copper	.96	.16	High

4.23 % Organic matter in soil

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So I need to find fertilizer with a similar ratio to 1.3:1.2:2.1 ( 1:1:2 or 1:1:1 ).Then I want to match the nitrogen needed. 1.3 lbs per 1,000 sqft.I have ~5,000 sqft of lawn and garden so 1.3 * 5 = 6.5 lbs N are needed.Now fertilizer is sold in volume per weight so a bag of 10:10:10 is 10% N. A 20 lb bag would give me 2 lbs of N, I’d need a little more than 3 bags spread evenly over the lawn and gardens. The Extension recommends matching the ratio as close as you can, then buying the correct amount of N.

Since Nitrates are the most important of the plant nutrients and mine were below Extremely Low on the chart I’m not surprised some plants are showing nutritional problems. The recommendation is to put out 1.3 lbs Nitrogen, 1.2 lbs Phosphorus, 2.1 lbs Potassium/1,000 now, and 1.3 lbs Nitrogen/1,000 monthly.

I received a separate recommendation for garden, roses and lawn. But I’m removing the lawn and the rose and garden recommendations were the same. So I’ll just follow those.

Soil conductivity runs from 0-5 for sandy soils, 5-25 for topsoils, and 10-1000 for clay soils. Soil conductivity measures the amount of soluble salts in a soil. Some plants are sensitive to high salts in the soil. Too much may also inhibit seed germination. Usually high salts are caused from too much fertilizer being added to the soil.

To convert umho/cm to ppm multiply your umho/cm * 640 then divide by 1000. So we have about 116 ppm salts in the soil, which is fine. Until it goes over 1400 ppm you shouldn’t see a problem. But remember some plants are very sensitive to salt so it depends on your plant.

Fresh water (1000)< Brackish ( 10,000 )< Saline ( 100,000)< Brine ( 100,000)

Organic matter breaks down quickly in Houston’s climate. Organic matter usually ranges between 2% to 8%. The more there is the better. If it is less than 2% you’ll want to add some organic matter ( compost, mulch, leaves etc ). There are several methods for testing organic matter. So if you are trying to compare from year to year, use the same lab to do the testing.

Healthy soil helps control rain water, preventing run off by absorbing the water. It sustains plant and animal life. It filters pollutants. Soil cycles nutrients and provides a support structure for plants.

When the Soil Food Web is in balance you have healthier plants. A healthy soil has anywhere from 100 million to 1 billion bacteria per teaspoonful. There are also several square meters of fungi, several thousand protozoa, about 2 to 3 dozen nematode bacterial feeders, a few fungi feeding nematodes and a few predatory nematodes. That’s quite the little zoo of critters.

Old forests have about 1000 fungi:100 bacteria in the soil under them
Deciduous trees 100 fungi: 5 bacteria in the soil under them
Shrubs and vines contain 5 fungi: 2 bacteria in the soil under them
Grass is about 1 fungi: 1 bacteria
Vegetables .75
Weeds .1

Which means if you have lots of weeds you want to look at your soil. Weeds are nature’s way of re-balancing the bacteria in the soil. Add some organic matter to your soil if weeds are a big problem.

In a healthy soil, bad organisms that harm your plants will be eaten by the good organisms. Nutrients will be retained in a form and amount that can be used by your plants.

To keep healthy soil you need organic material and you need to avoid tilling, pesticides, herbicides and chemical fertilizers. If you apply a thin layer of compost over your soil it will prevent erosion. When it rains the earth worms will come up, and pull down some of that compost into the soil.

More information:
Natural Resources Conservation Service: Soil

I know you’ve all heard of pH and those of you with pools are probably very familiar with pH. But why do you care about your garden soil pH?

The ‘p’ in pH stands for ‘potenz’ ( potential to be ) and the ‘H’ is for ‘Hydrogen’. So pH is just a measure of the amount of hydrogen in your soil. The scale runs from 0 to 14 ( acidic to alkaline ) and you are aiming for 6-7 but your plants will be thrilled with anything between 6-8.

I have no idea what my soil pH is, I’m waiting for my soil test to come back. However I’m told the Houston area has acidic soil, most everything north and west of us has alkaline soil.

The pH is important to plants because plant nutrients are not soluble when the pH is too high or too low. 98% of the nutrients your plant needs it gets when the roots take in water. If the pH is too high or too low the nutrients in the soil do not dissolve and your plants can’t use them.

Think about being stuck on a plane. You have a bag of cookies in a sealed plastic bag and nothing sharp to slice the bag open. You have the food but no way to eat it. This is what happens to your plants when your soil’s pH is too far from center.

If your soil tests below 6.0 you’ll want to add limestone to your garden. The amount you add depends on how acidic your soil is. Limestone takes a very long time to work its way down into the soil so it may take a while to see your results.

If your soil is about 8.0 you’ll need to add sulfur to it to lower the pH. This also is a very slow process. If you add to much sulfur too quickly you’ll wipe out your plants.

pH should be checked yearly. ( Yes, I know, I’ve been gardening forever and this is my first year testing but better later then never. It just shows you can teach an old gardener new tricks. ) You can send a sample to the county for testing. Many garden supply places carry soil pH kits.