Relentless Gardner

You probably already guessed that cool-season crops benefit the most from partial shade. But why is shade more beneficial to some vegetables than others? There are two reasons. One, shade keeps the the leafy vegetables such as kale, lettuce, and spinach more tender. With less sunlight, the plants will not grow to the same size as they would with more sun. Naturally, the more sun, the more energy and photosynthesis the plant produces.

What is partial shade in terms of hours of sun per day? Partial shade is less than six hours of sun but a minimum of four hours. When we define full sun, this means more than six hours and a maximum of eight hours. Afternoon shade can be a minimum of four hours. Dappled or filtered light through tree leaves can be considered two hours of sun exposure.

Some root crops such as radishes and turnips need partial shade to reduce the amount of foliage that affects the amount of root production. The ideal situation for these crops is morning sun for up to four hours and afternoon shade for up to four hours. Carrots, radishes and beets are other root crops that would do well in the morning sun and afternoon shade.

Depending on the soil, the shade helps crops retain moisture longer than in the sun. However, the soil needs to be friable and well-drained. Otherwise, crops can be overwatered and create slugs and snails that will damage the crops. Be sure that the soil where beets are planted gets the chance to dry out between waterings. Beets can do well in dry shade.

The ideal situation for lettuce and greens is morning sun and afternoon shade. With these vegetables, exposure to afternoon sun can cause a bitter taste in the lettuce leaves and the greens. Besides lettuce and greens do not like drought and keeping them in the afternoon shade helps keep the soil moist. Hot and dry weather can cause them to bolt sooner.

If you do not have a nearby tree to help shade the vegetable garden in the afternoon, then consider a shade cloth or a low tunnel where you can pull the shade cloth over the lettuce greens or other crops in the afternoon.

Consider your elevation when planting a vegetable garden. The higher the elevation, the shorter the season, and the lower the elevation the longer the season. Higher elevations have stronger sun and face the risk of sunscald on vegetables.

Linda Langelo is a Colorado State University Extension horticulture specialist, member of Garden Communicators International and regular contributor to MarthaStewart.com gardening articles. She also produces The Relentless Gardener Podcast. She is a guest blogger for AARP Colorado and AARP Maryland.