What is lime, and why does the garden need it?
Garden lime is limestone that has not been heated to produce the more reactive forms of lime such as quicklime and slaked lime. Garden lime is used to raise the pH of soil, and also to provide plants with the calcium they sometimes need. 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.
Which plants need lime?
While many plants prefer and flourish in low pH (acidic) soils, there are some that do not. For these plants, soils that are too acidic slow or even block their 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. 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.
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.
Should I apply lime in my vegetable garden?
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.
When should I apply lime?
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.
Fall is the best time to lime your lawn. Lime will promote great lawn health, and reduce moss build-up. 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.
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.