Valley Seed Company

Garden Health

Soil Testing and Amending

WHY soil test?

Getting a soil test is a great way to measure its health and fertility. These tests are generally inexpensive, and well worth any cost when it comes to growing and maintaining healthy plants in the garden.

Most soil nutrients are readily found in the soil provided that its pH is within the 6-6.5 range. However, when the pH rises, many nutrients (like phosphorus, iron, etc.) may become less available. When it drops, they may even reach toxic levels, which can adversely affect the plants.

Doing a soil test helps take the guesswork out of fixing any of these nutrient issues. There’s no need to spend money on fertilizers that aren’t necessary. There’s no worry of over fertilizing either. With a soil test, you’ll have the means for creating a healthy soil environment that will lead to maximum plant growth.

A soil test can determine the current fertility and health of your soil. By measuring both the pH level and pinpointing nutrient deficiencies, a soil test can provide the information necessary for maintaining the most optimal fertility each year.

Most plants—including grasses, flowers, and vegetables—perform best in slightly acidic soil (6.0-6.5). Others, like azaleas, gardenias and blueberries, require a somewhat higher acidity in order to thrive. Therefore, having a soil test can make it easier to determine the current acidity so you can make the needed adjustments. It will also guide you in fixing any deficiencies that may be present.

Soil testing can be done about any time of year but is best done in the fall after growing season. This gives you time to make any needed adjustments for next year’s garden.

You should avoid having the soil tested whenever it is wet or when it’s been recently fertilized. To take a sample for testing garden soil, use a small trowel to take thin slices of soil from various areas of the garden (about a cup’s worth each). Allow it to air dry at room temperature and then place it into a clean plastic container or Ziploc baggie. Label the soil area and date for testing.

Soil Ph

The importance of having a balanced Ph before adding fertilizers (amending) to your soil cannot be over stressed.

The soil pH rating can be the main key to a plant of any kind doing exceptionally well, just getting by, or heading towards death.  Soil pH for plants is crucial to their health.

Soil pH is a measurement of the alkalinity or acidity of the soil. The soil pH range is measured on a scale of 1 to 14, with 7 as the neutral mark. Anything below 7 is considered acidic soil and anything above 7 is considered alkaline soil.

The middle of the range on the soil pH scale is the best range for bacterial growth in the soil to promote decomposition. The decomposition process releases nutrients and minerals into the soil of our plants, making them available for the plants or bushes to use. Soil fertility depends on pH. The mid- range is also perfect for micro-organisms that convert the nitrogen in the air into a form which the plants can readily use.

When the pH rating is outside the mid-range, both of these extremely important processes become more and more inhibited, thus locking up the nutrients in the soil of our plants so that the plant cannot absorb them and use them to their full advantage.

Testing Soil pH

Soil pH can get out of balance for several reasons. The sole use of inorganic fertilizers will cause the soil to be more acidic over time from continued applications. Using a rotation of inorganic and organic fertilizers will aid in keeping the soils pH from getting out of balance.

Adding amendments to the soil can also alter the soil’s pH rating. Testing soil pH of the garden occasionally and then making the appropriate soil pH adjustment based on those tests is highly recommended in order to keep things in balance.

Maintaining the pH balance will allow the various plants to be hardier and allows the gardener to enjoy top quality blooms and vegetable or fruit harvests.

Flower Preferred pH Range
Ageratum 6.0 – 7.5
Alyssum 6.0 – 7.5
Aster 5.5 – 7.5
Carnation 6.0 – 7.5
Chrysanthemum 6.0 – 7.0
Columbine 6.0 – 7.0
Coreopsis 5.0 – 6.0
Cosmos 5.0 – 8.0
Crocus 6.0 – 8.0
Daffodil 6.0 – 6.5
Dahlia 6.0 – 7.5
Daylily 6.0 – 8.0
Delphinium 6.0 – 7.5
Dianthus 6.0 – 7.5
Forget-Me-Not 6.0 – 7.0
Gladiola 6.0 – 7.0
Hyacinth 6.5 – 7.5
Iris 5.0 – 6.5
Marigold 5.5 – 7.0
Nasturtium 5.5 – 7.5
Petunia 6.0 – 7.5
Roses 6.0 – 7.0
Tulip 6.0 – 7.0
Zinnia 5.5 – 7.5

Soil pH for Herbs

Herbs Preferred pH Range
Basil 5.5 – 6.5
Chives 6.0 – 7.0
Fennel 5.0 – 6.0
Garlic 5.5 – 7.5
Ginger 6.0 – 8.0
Marjoram 6.0 – 8.0
Mint 7.0 – 8.0
Parsley 5.0 – 7.0
Peppermint 6.0 – 7.5
Rosemary 5.0 – 6.0
Sage 5.5 – 6.5
Spearmint 5.5 – 7.5
Thyme 5.5 – 7.0

Soil pH for Vegetables

Vegetable Preferred pH Range
Beans 6.0 – 7.5
Broccoli 6.0 – 7.0
Brussels Sprouts 6.0 – 7.5
Cabbage 6.0 – 7.5
Carrot 5.5 – 7.0
Corn 5.5 – 7.0
Cucumber 5.5 – 7.5
Lettuce 6.0 – 7.0
Mushroom 6.5 – 7.5
Onion 6.0 – 7.0
Peas 6.0 – 7.5
Potato 4.5 – 6.0
Pumpkin 5.5 – 7.5
Radish 6.0 – 7.0
Rhubarb 5.5 – 7.0
Spinach 6.0 – 7.5
Tomato 5.5 – 7.5
Turnip 5.5 – 7.0
Watermelon 5.5 – 6.5


Garden Helpers

Epsom Salt—so inexpensive and readily available, but so overlooked.

Epsom salt helps improve flower blooming and enhances a plant’s green color. It can even help plants grow bushier. Epsom salt is made up of hydrated magnesium sulfate (magnesium and sulfur), which is important to healthy plant growth.

Even if you don’t believe in its effectiveness, it never hurts to try it. Magnesium allows plants to better take in valuable nutrients, like nitrogen and phosphorus.

It also helps in the creation of chlorophyll, which is vital for photosynthesis. In addition, magnesium greatly improves a plant’s ability to produce flowers and fruit.

If the soil becomes depleted of magnesium, adding Epsom salt will help; and since it poses little danger of overuse like most commercial fertilizers do, you can use it safely on nearly all your garden plants.

Simply substitute it for regular watering either once or twice a month. Keep in mind that there are a number of formulas out there, so go with whatever works for you.

Before applying Epsom salt, however, it’s a good idea to have your soil tested to determine whether it’s deficient of magnesium. You should also be aware that many plants, like beans and leafy vegetables, will happily grow and produce in soils with low levels of magnesium. Plants like rose, tomatoes and peppers, on the other hand, require lots of magnesium and, therefore, are more commonly watered with Epsom salt.

When diluted with water, Epsom salt is easily taken up by plants, especially when applied as a foliar spray.* Most plants can be misted with a solution of 2 tablespoons of Epsom salt per gallon of water once a month. For more frequent watering (every other week) cut this back to one tablespoon.

With roses, you can apply a foliar spray of 1 tablespoon per gallon of water for each foot of the shrub’s height. Apply in spring as leaves appear and then again after flowering.

For tomatoes and peppers, apply 1 tablespoon of Epsom salt granules around each transplant or spray (1 tbsp. per gallon) during transplanting and again following the first bloom and fruit set. Hint: For sweeter tomatoes add in 1 tbsp. raw sugar to the fertilizer mix. Don’t use this mix as a foliar spray—ants and other sweet eaters will be overly attracted to the plants.

*foliar spraying is best done in early morning or later afternoon when the sun is low to the horizon and not so likely to burn the plant from the water acting like a magnifying glass.

Technically, magnesium is a metallic chemical element which is vital for human and plant life. Magnesium is one of thirteen mineral nutrients that come from soil and when dissolved in water, is absorbed through the plant’s roots. Sometimes there are not enough mineral nutrients in the soil and it’s necessary to fertilize in order to replenish these elements and provide additional magnesium for plants.

How Do Plants Use Magnesium?

Magnesium is the powerhouse behind photosynthesis in plants. Without magnesium, chlorophyll cannot capture sun energy that is needed for photosynthesis to occur. In short, magnesium is required to give leaves their green color. Magnesium in plants is located in the enzymes, in the heart of the chlorophyll molecule. Magnesium is also used by plants for the metabolism of carbohydrates and in the cell membrane stabilization.

Magnesium Deficiency in Plants

The role of magnesium is vital to plant growth and health. Magnesium deficiency in plants is common where soil is not rich or is very light in organic matter.

Heavy rains can cause a deficiency to occur by leaching magnesium out of sandy or acidic soil. In addition, if soil contains high amounts of potassium, plants may absorb this instead of magnesium, leading to a deficiency.

Plants that are suffering from a lack of magnesium will display identifiable characteristics. Magnesium deficiency appears on older leaves first as they become yellow between the veins and around the edges. Purple, red or brown may also appear on the leaves. Eventually, if left unchecked, the leaf and the plant will die.

Providing Magnesium for Plants

Providing magnesium for plants begins with annual applications of rich, organic compost. Compost conserves moisture and helps keep nutrients form leaching out during heavy rainfall. Organic compost is also rich in magnesium and will provide an abundant source for plants.

You can use chemical leaf sprays as a temporary solution to provide magnesium but that defeats the whole reason behind growing organic.


Understanding nitrogen requirements for plants helps gardeners supplement crop needs more effectively. Adequate nitrogen soil content is necessary for healthy plants. All plants require nitrogen for healthy growth and reproduction. More importantly, plants use nitrogen for photosynthesis. While native plants are better adapted to their surroundings and oftentimes less affected by nitrogen deficiency, in plants such as vegetable crops, supplemental nitrogen may be required.

Nitrogen Deficiency in Plants

Good crops depend on an adequate supply of nitrogen. Most nitrogen is naturally present in the soil as organic content. Nitrogen deficiency in plants is more likely to occur in soils that are low in organic content. However, nitrogen loss due to erosion, runoff and leaching of nitrate will also cause nitrogen deficiency in plants.

Some of the most common symptoms of nitrogen deficiency in plants include the yellowing and dropping of leaves and poor growth. Flowering or fruit production may also be delayed.

Nitrogen Requirements for Plants

As organic matter decomposes, nitrogen is slowly converted to ammonium, which is absorbed by plant roots. Excess ammonium is turned into nitrate, which plants also use to produce protein. However, unused nitrates remain in the groundwater, resulting in leaching of the soil.

Since nitrogen requirements for plants vary, supplemental nitrogen fertilizer should only be used in the correct proportion. Always check the nitrogen analysis on fertilizer packaging to determine the percentage amount of nitrogen present. This is usually the first of three numbers on the package (10-30-10).

Raising Soil Nitrogen

There are several ways to add nitrogen to soil. Supplemental nitrogen is usually provided by using organic or chemical fertilizers. Plants obtain nitrogen through compounds containing ammonium or nitrate. Both of these can be given to plants through chemical fertilizers. Using chemical fertilizer to add nitrogen to soil is faster; however, it is more prone to leaching, which can be harmful to the environment.

Building up levels of organic matter in the soil is another way of raising soil nitrogen. This can be achieved by using organic fertilizer in the form of compost or manure. Growing legumes can also supplement soil nitrogen. Although organic fertilizer must be broken down in order to release compounds containing ammonium and nitrate, which is much slower, using organic fertilizer to add nitrogen to soil is safer for the environment.

High Nitrogen in Soil

Too much nitrogen present in the soil can be just as harmful to plants as too little. When there is high nitrogen in soil, plants may not produce flowers or fruit. As with nitrogen deficiency in plants, the leaves may turn yellow and drop. Too much nitrogen can result in plant burning, which causes them to shrivel and die. It can also cause excess nitrate to leach into groundwater.

All plants need nitrogen for healthy growth. Understanding the nitrogen requirements for plants makes it easier to meet their supplement needs. Raising soil nitrogen for garden crops helps produce more vigorous-growing, greener plants.

The importance of Phosphorous in the soil.

The function of phosphorus in plants is very important. It helps a plant convert other nutrients into usable building blocks with which to grow. Phosphorus is one of the main three nutrients most commonly found in fertilizers and is the “P” that is listed on fertilizers.

Phosphorus Deficiency in the Soil

How can you tell if your garden has a phosphorus deficiency? The easiest way to tell is to look at the plants. If your plants are small, are producing little or no flowers and have a bright green or purplish cast to them, you have a phosphorus deficiency. Since most plants in the garden are grown for their flowers or fruit, replacing phosphorus in the soil if it is lacking is very important.

There are many chemical fertilizers that can help you with replacing phosphorus and getting a good nutrient balance in your soil. When using chemical fertilizers, you will want to look for fertilizers that have a high “P” value (the second number in the fertilizer rating N-P-K).

If you would like to correct your soil’s phosphorus deficiency using organic fertilizer, try using bone meal or rock phosphate. These both can help with replacing phosphorus in the soil. Sometimes, simply adding compost to the soil can help plants be better able to take up the phosphorus that is already in the soil so consider trying that before you add anything else.

Regardless of how you go about replacing phosphorus in the soil, be sure not to overdo it as extra phosphorus can run off into the water supply and is a major pollutant.

High Phosphorus in Your Soil

It is difficult for a plant to get too much phosphorus due to the fact that it is difficult for plants to absorb phosphorus in the first place.

There is no understating the importance of phosphorus in plant growth. Without it, a plant simply cannot be healthy. The basic function of phosphorus makes it possible to have beautiful and abundant plants in our gardens.

Potassium & Plants

Plants and potassium is actually a mystery to even modern science. The effects of potassium on plants is well known in that it improves how well a plant grows and produces but exactly why and how is not known. As a gardener, you do not need to know the why and how in order to be hurt by a potassium deficiency in plants.

Effects of Potassium on Plants

Potassium is important to plant growth and development. Potassium helps:

  • Plants grow faster
  • Use water better and be more drought resistant
  • Fight off disease
  • Resist pests
  • Grow stronger
  • Produce more crops

With all plants, potassium assists all functions within the plant. When a plant has enough potassium, it will simply be a better overall plant.

Signs of Potassium Deficiency in Plants

Potassium deficiency in plants will cause a plant to perform more poorly overall than it should. Because of this, it can be difficult to see specific signs of potassium deficiency in plants.

When severe potassium deficiency happens, you may be able to see some signs in the leaves. The leaves, especially older leaves, may have brown spots, yellow edges, yellow veins or brown veins.

What is in Potassium Fertilizer?

Potassium fertilizer is sometimes called potash fertilizer. This is because potassium fertilizers often contain a substance called potash. Potash is a naturally occurring substance that occurs when wood is burned.

While potash is technically a naturally occurring substance, only certain kinds of potassium fertilizers containing potash are considered organic.

Some sources refer to high potassium fertilizer. This is simply a fertilizer that is exclusively potassium or has a high “K” value.

If you want to add potassium to your soil at home, you can do it in several ways without having to use potash or other commercial potassium fertilizer. Compost made primarily from food byproducts is an excellent source of potassium. In particular, banana peels are very high in potassium.

Wood ash can also be used, but make sure that you apply wood ash only lightly, as too much can burn your plants.

Greensand, which is available from most nurseries, will also add potassium to you garden.

Because potassium deficiency in plants can be hard to spot through looking at the plant, it is always a good idea to have your soil tested before adding more potassium.


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