Lime in Fall

What is Garden Lime and Why Does it Matter?

Garden lime is limestone that has not been heated to produce the more reactive forms of lime such as quicklime and slaked lime. It’s main uses are:

  • To raise the pH of soil
  • Provide plants with the calcium they sometimes need to grow strong

It is available in two broad types – calcium carbonate lime (often sold as “ag lime” or “garden lime”) and dolomite, which has more magnesium carbonate and less calcium carbonate.

While many plants prefer and flourish in low pH (acidic) soils, there are some that do not. For these plants, if the soil has too low of pH, then it can slow or even block the plants ability to take up key nutrients such as nitrogen.  Applying lime to make the soil pH neutral (or for some even slightly alkali) lets them access these nutrients again.

Which Plants Like Neutral to Alkali Soil pH?

In our area, only a few common landscape plants – like lilacs and daphne – really hate acidic soils, but several others will grow better when soil is not too acidic, including rose-of-sharon (Hibiscus syriacus), clematis, mock orange, weigela, ceanothus, potentilla, deutzia, and many hellebores.

Lime for the Lawn & Landscape

The largest homeowner use of garden lime is the lawn.  While lawn grasses are reasonably adaptable, they grow better when soils are neutral to slightly alkaline; and controlling the soil acidity can also reduce moss development. Fall is the best time to lime your lawn.

Lime is a relatively slow acting product, so we recommend applying lime to change pH in the fall for lawns, shrubs, and perennials.  If your soil is strongly acidic (pH below 5.5), then you might want to apply a second dose in the spring.

For lawn and landscape, either calcium lime or dolomite will work fine.  Apply about 12  pounds of granular lime per 1000 square feet of lawn; for landscape plants the amount may vary from about 1/4 cup for perennials or young plants, up to a couple of cups around a very large lilac or mock orange.

Lime for the Edible Garden

In the vegetable garden, the goal is to provide calcium, so use calcium carbonate lime.  Apply lime at planting, and again about halfway through the season – about 4th of July works, and is easy to remember.  Try a handful (about 1/8 to 1/4 cup) per plant per application, mixed right into the soil at planting time, or applied as a ring around the plant and then lightly raked in.

Using lime as a source of calcium is important in the vegetable garden. Many garden plants – notably tomatoes, but also squash, melons, and cucumbers – show distinct symptoms or even total failure if not enough calcium is available.