Adding mulch to vegetable gardens

Preparing for the gardening season invariably includes weed and water management. Useful tools, besides the hose and hoe, are mulches. Once vegetable plants have sprouted and are three to four inches tall, the use of a mulch can reduce weeding, keep the soil cool, reduce pathogens and help maintain even soil moisture and temperature.

Mulching guru Ruth Stout suggested in her book “Gardening Without Work” that mulches will decompose into the soil and more must be added through the season. The mulch will add to soil organic matter and enrich the soil.

The Tomato Bible website reports organic mulches such as dried lawn clippings, compost, aged manure, old hay or straw and cardboard are all useful. 

Warm weather crops benefit from mulches by reducing water splashing onto the plant which can cause blight and keeps fruits off the soil which limits rot. The Tomato Bible said even soil moisture and temperature is beneficial to all plants. 

According to the website Harvest to Table, cool weather crops such as broccoli, cabbage, lettuce and greens will respond well because mulching can reduce soil temperature by up to 10 degrees. Reducing soil temperature with mulches can help these cool loving plants to get through the heat of the summer.

Mulch acts as an insulating layer for the soil so evaporation from bare soil is lessened. Watering may be less frequent but must still be consistent. It is important to check under the mulch to make sure that there is sufficient watering, then use that watering time to plan subsequent irrigation to ensure it is consistent.

A layer of mulch two – four inches deep is sufficient for young plants. This will impede light from the soil surface, which weeds need to germinate. If any weeds do poke through, the soil will be fairly loose and the weeds should pull up easily. Mulch should be placed throughout the row and kept three to four inches from the base of the plants so there is sufficient air circulation.

Blossom end rot is a disease of fruiting vegetables such as tomatoes, peppers, summer squash and cucumbers. Due to soil mineral imbalances and sporadic watering, the end of the fruit turns mushy and rots. Mulching supplies soil moisture balance that will help control this situation, said savvygardener.com.

During 30 years of experience in the vegetable garden, I have seen excellent results to prevent blossom end rot using Epsom salts and powdered eggshells and mulching. To do this, dig the planting hole a few inches deeper than normal, put a small handful or about 1/8 cup of powdered eggshells and an equal amount of Epsom salts in the hole. Stir it around in the bottom of the hole and cover with two inches of soil. Then place the plant in the hole and continue as normal. To make powdered eggshells, first dry the eggshells used in cooking and then use a blender to make powder.

 When utilizing organic matter such as dried lawn clippings, compost or old hay or straw, it is very important to know the source of the material. Oregon State University (OSU) Extension Service states that herbicide carryover happens when animals that are fed hay that was sprayed with herbicides, the herbicide survives the digestive processes and may contaminate the compost. Likewise, lawns where herbicide products were used may allow for herbicide carryover in the grass clippings.

The results of herbicide carryover may include misshapen, poor producing or weak plants. The solution is to remove the mulch and dispose of it where it will not come in contact with garden soil again.

According to the OSU Extension Service, there is a simple home test that gardeners can use to determine herbicide presence in soil or compost. 

Collect a small shovelful of the compost or manure from several parts of the pile. Mix compost and potting soil 2:1 and place it into 8-10 small planting pots. Fill 4 small pots with plain potting soil as a control. Plant 2-3 bean or pea seeds in each pot. Give each pot its own saucer so there is no cross contamination with draining water. Water and care for them as usual. Observe the seedlings as they sprout. If the plants are strong and healthy by the time they have two - three sets of leaves, the compost should be clean. If the seedlings show any weakness or misshapen leaves and stems, there is likely herbicide in the compost and it should not be used for broadleaf plants.

Jean Pocha is a certified Master Gardener in Montana and lives in Helmville.  She is happy to answer reader questions.  Please email questions to jean@seeleylake.com