Another Rainy Year in the Garden: How to Future-Proof Your Landscape

Based on 126 years of statewide average rainfall data, 2020 was the second wettest year on record, with 2018 being the wettest. 2021 has just gotten started, but it looks like we may be in for another record-breaking year in terms of heat and precipitation. This is not good news for anyone with a yard.

Everyone knows that for plants to grow and stay healthy, they require water and sunlight. However, it’s a lot more complicated than that. Excess water in the soil leaves no room for oxygen, a key component for plant metabolism. In school, children learn that humans breathe out carbon dioxide and breathe in oxygen, whereas plants “breathe” in carbon dioxide and release oxygen, but plants actually require a significant amount of oxygen as well, and they take it in through the roots as well as through the stomata (small pores) in leaves. When we have excessive rain, the soil is unable to drain fast enough and becomes waterlogged, which suffocates plant roots. After some period of time, the roots will begin to die.

The length of time a plant can survive in waterlogged soil depends on the species and the conditions under which it evolved. Some trees such as river birch, sycamore, and bald cypress naturally grow near (or in the case of bald cypress, in) bodies of water, so they can handle having “wet feet”. Other plants, such as those that grow in high altitudes where the air is less humid and the water table is lower, like azaleas, mountain laurel, or pasqueflower, will die quickly when exposed to boggy conditions. If you have plants in your landscape that aren’t tolerant of wet soils, you can expect there may be some losses this year. The larger the plant, the longer it will take to show decline, and for large trees it can actually take up to several years to die from lack of oxygen in the roots.

Another issue caused by wet weather is increased fungal diseases. Wet weather triggers spore production in fungi, and many fungal pathogens are spread through water droplets splashing between plants and into injured areas or new growth that has less protection than mature branches or leaves. To reduce infections, make sure you only prune during dry weather, and prune off broken branches that could provide an opening for disease to take hold.

The climate in North Carolina ranges from the colder, drier mountains in the west through the swampy coastal plains in the east. The piedmont in the center of the state has historically been the best of both worlds where a broad range of plants could be grown, but with warmer and wetter conditions each year, that may be changing. For established plantings, there isn’t much that can be done to protect plants from wet weather, but there are some things to take into considerations when adding new plants. Here are some tips for future-proofing your garden: 

• Wet weather promotes fungal diseases, so make sure you are NOT pruning during rainy weather. The cuts create an opening for pathogens to infect your plants, and the rain washes the pathogen right in.

• Some fungal diseases require two different plant species, such as cedar-apple rust. As long as you don’t have both plants in your landscape, the disease cannot occur.

Cedar-apple rust on an eastern red cedar.

• Select native plants or plants from very similar climates (such as central mainland Japan). Alpine wildflowers and many evergreen trees such as Colorado blue spruce do not handle the hot, humid, rainy summers of the south. Some plants that used to survive in NC may not as it continues to get hotter and wetter. Look toward the coast or further south for inspiration, but be aware that many coastal plants prefer sandy soils and not the clay that we have here in the piedmont.

• Amend your garden soil with substrates that improve drainage and porosity, such as compost, fine shredded pine bark, and expanded slate.

Expanded slate is an excellent amendment for garden soils, because it can hold nutrients, unlike most gravels.

• Plant in raised beds or mounds to increase drainage. You can see mounded gardens at local botanical gardens such as JC Raulston Arboretum and Juniper Level Botanical Garden, once they are open to visitors again.

Mounded beds at Juniper Level Botanical Garden.

• Turn low, boggy areas of your yard into rain gardens. Incorporate dry creek beds that can funnel water away when needed, or even a French drain to help water absorb into the ground. There are lots of new books on how to build rain gardens, including this one by NC State professors Helen Kraus and Anne Spafford: Rain Gardening in the South.