A Guide to Soil pH for Vegetable and Flower Gardening

Before you get those plants and flowers into the ground, it all begins with good soil. One way to ensure a bumper crop is to know whether its pH balance needs an amendment to make it more acidic or more alkaline. Keeping it at the right level plays a big role in supporting the flowers and vegetables you want to grow this summer.

Why does soil pH matter?

The soil’s pH level affects how nutrients dissolve into the soil, becoming available to the roots. If the soil’s pH level falls outside the plant’s ideal range, that affects its ability to thrive.

The pH scale has 14 points, with 7.0 in the neutral middle. When you’re talking about soil, anything that falls below 7.0 is acidic, and a reading above 7.0 is alkaline.

Most soils in the Midwest fall within 6.0 to 7.0 on the pH scale, and most flowers and vegetables that people raise in their gardens are happy in that range. However, when the levels rise above a pH of 7.0, plants start to struggle. Bare spots and excessive weeds are telltale signs of overly acidic soil.

Soil pH for growing flowers

Most flowers in the U.S. will thrive very nicely in slightly acidic soil, though many varieties can thrive even in alkaline soils, including daylilies, cosmos and geraniums. It’s important to know certain flowers prefer more acidic soils.

• Azaleas (4.0-5.5 pH)
• Rhododendrons (4.0-5.5 pH)
• Blue hydrangeas (5.2-5.5 pH) (Note: Not all hydrangea flowers turn blue from adding soil amendments, so it's important to know the species)

Soil pH for growing food

Most vegetables thrive in soils that are on the acidic side of the balance, and Midwestern soils tend to fall within the 6.0-7.0 range. But there are a few exceptions to be aware of.

• Potatoes and sweet potatoes (4.8-5.5 pH)
• Rhubarb (5.5-6.5 pH)
• Blueberries (4.0-5.0 pH)

Put your soil to the test

If you’re growing plants that need acidic soil, or if your garden plants are not thriving as they should, a simple soil test can guide the gardener on next steps for a successful growing season. Checking the pH level with a kit is a great starting point.

A test kit, like the Soil Test Kit, gives your soil’s pH, as well as its nitrogen, phosphorus and potassium levels, so you’ll know before planting what your soil needs.

If you need to monitor a plot on an ongoing basis, Soil pH Meter is a handheld device that gives you an instant reading of your soil’s pH level.

Amendments for alkaline soils

Liquid soil acidifiers: These products are ideal for smaller plots, but they need frequent reapplication, about every month or so.

Iron sulfate: A go-to for correcting alkaline soils. Granular Iron Sulfate can be used both in the garden and on the lawn.

Aluminum sulfate: A less expensive option to correct alkaline soil, or create the ideal acidic soil conditions for things like azaleas. Avoid using with phosphate fertilizer because it can “tie up” the aluminum and you may not get the results you’re looking for. Try Granular Aluminum Sulfate.

Elemental sulfur: Ideal for acidifying the soil for growing blueberries and hydrangeas, incorporate 6 inches deep in the soil before planting. Granular Soil Acidifier can be reapplied every six weeks to maintain the ideal soil conditions.

Organic compounds: It can be as simple as incorporating compost and decaying garden leaves into your plots. Sphagnum Peat Moss breaks down into the soil slowly and retains moisture. Composted mixes feature an organic blend of natural products to nourish flowers and veggies.

Amendments for acidic soils

Agricultural lime: Lawn & Garden Lime helps aerate hard clay soils and replenishes calcium, without burning plant roots.

Hydrated lime: Faster acting than agricultural lime, hydrated lime can also reduce excessive weeds (a clear sign of too-acidic soil).

When it comes to balancing your soil’s pH, Fleet Farm’s Lawn and Garden department has you covered!