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ADJUSTING ROSEBED pH


Stan V. (Stan the Rose Man) Griep, ARS Certified Consulting Rosarian
Photographs Stan V. (Stan the Rose Man) Griep


Last month we discussed the best site for a new rose bed and preparation of a new site to get roses off to their best growth. This month we learn about soil makeup including how to attain the best pH for growing roses.

If the soils are heavy or clayey, we will need to add a clay buster amendment to the soil. The clay buster amendments have a mix of organic materials in them that help to break up the clay, which makes for a lighter thus better draining soil. I have added a bag or two of play sand or landscaping sand to the soil in such cases as well, to help loosen up the soil. I like to add some bags of a good quality compost, such as a bagged compost called EKO Compost, to the new rose bed soil. Mushroom compost works well too for this use. Along with these amendments, I will add a few bags of top soil or bulk top soil from a landscape supply center. If the bulk pile of top soil at the landscape center has weeds growing on top of it, try to get your soil from an area well underneath to avoid the weed seeds. 

Spread the amendment materials out over the top of the tilled soil as uniformly as possible. Raking it out with a hard-toothed rake to even it up is a good idea. Now grab the tiller or garden fork again and work the amendments well into the rose bed soil. Reach down, take a big handful of the soil from time to time, and see how truly loose and workable it has become. If the soil still feels a bit heavy and clumpy, work the amendments in some more.

Once the soil is nicely loosened up, I like to sprinkle some alfalfa meal over the top of the soil, just enough so that there is a light green coloration to the soils surface. Adding a light dusting of kelp meal at this time is another fine thing to do. Now it is time to grab the garden fork again and work in the alfalfa and kelp meal. You will want to work these additives well down into the soil for optimum performance. After having worked the soil well again, sprinkle down the entire new rose bed area with water. Use just enough water to settle things in and add just enough moisture to help get all the additives and amendments working in with the native soil, but not so much as to make things muddy. 

I like to do this sort of new rose bed preparation in the fall preceding the next spring’s plantings. Thus, the native soils and amendments have a chance to be well activated over the late fall and winter months. However this new rose bed preparation can be done in the early spring as well, I like to leave the soil sit and get activated for at least 10 days prior to planting the new rosebushes in the new bed. Test the soil’s pH after the 10 days or in early spring if the fall soil preparation was done then.

When one brings up the topic of soils for roses, there are some definite concerns with the composition of the soils that make them their best for growing rosebushes and having them perform well. We know that the soil’s pH is optimum at 6.5 on the pH scale (pH range 5.5 – 7.0). The soil’s pH may be either too acidic or too alkaline, so what do we do to effect the desired change in the pH?

To make soils less acidic, the common practice is to apply a material that contains some form of lime. Ground agricultural limestone is most frequently used. The finer the limestone particles, the more rapidly it becomes effective. Different soils will require a different amount of lime to adjust the soil pH value. The texture of the soil, organic matter content and the plants to be grown are all factors to consider in adjusting the pH value. For example, soils that are low in clay typically require less lime than soils high in clay to make the same pH change.

Two materials commonly used for lowering the soil pH are aluminum sulfate and sulfur. These can be found at a garden supply center. Aluminum sulfate will change the soil pH instantly because the aluminum produces the acidity as soon as it dissolves in the soil. Sulfur, however, requires some time for the conversion to sulfuric acid with the aid of soil bacteria. The conversion rate of the sulfur is dependent on the fineness of the sulfur, the amount of soil moisture, soil temperature and the presence of the bacteria. Depending on these factors, the conversion rate of sulfur may be very slow and take several months if the conditions are not ideal. For this reason, most people use the aluminum sulfate. You can use the following tables to calculate the application rates for both the aluminum sulfate and the sulfur. The rates are in pounds per 10 square feet for a loamy soil. Reduce the rate by one-third for sandy soils and increase by one-half for clays.

 

Pounds of Aluminum Sulfate to Lower the pH

Desired pH

Present pH

6.5

6.0

5.5

5.0

4.5

8.0

1.8

2.4

3.3

4.2

4.8

7.5

1.2

2.1

2.7

3.6

4.2

7.0

0.6

1.2

2.1

3.0

3.6

6.5

-

0.6

1.5

2.4

2.7

6.0

-

-

0.6

1.5

2.1

 

Pounds of Sulfur to Lower the Soil pH

Desired pH

Present pH

6.5

6.0

5.5

5.0

4.5

8.0

0.3

0.4

0.5

0.6

0.7

7.5

0.2

0.3

0.4

0.5

0.6

7.0

0.1

0.2

0.3

0.4

0.5

6.5

-

0.1

0.2

0.3

0.4

6.0

-

-

0.1

0.2

0.3

Once the rosebushes are in the ground, it is wise to add a layer of mulch over the top of the rose bed soil to help retain the soil’s moisture. The mulch will also aid in the prevention of soil erosion from wind or hard rains.
 
If you have any questions about this subject please feel free to email me at rosebed7@gmail.com .

Stan V. Griep
ARS Certified Consulting Rosarian, Webmaster: The Colorado Rosarian, Green Cure Representative - CO
Member: American Rose Society, Member: Denver Rose Society, Member: Loveland Rose Society,
Honorary Member: The Rose Society of South Australia
Award Winning Rose Photographer, Rose Gardening Freelance Writer & Speaker
Visit The Colorado Rosarian Site: http://rosemanstansblog.wordpress.com/
Please Visit My On-Line Shop: http://www.zazzle.com/rosemanstansshop

Posted July 12, 2013



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