The root of the matter: Planting in fall for establishment and water savings

Rain: Our hope is that fall will bring the rain and take care of watering our newly installed plants for us. We still need to water them in when we plant them to settle the soil around the rootball, but if Mother Nature wouldn’t mind taking care of the watering after that, we’d appreciate it. Having some rainfall on the foliage helps keep these new plants hydrated while they’re getting over the shock of having moved house and starting to send new roots out to explore the new soil neighborhood. If the rain is not enough to wet the soil to the depth of the rootball, your new plants will benefit from some supplemental water while it gets established. If the rains haven’t come, you will need to water these plants to keep them alive until they’ve grown enough root mass below to support the rest of the plant aboveground. Still, we hope fall rains lessen the amount of water we need to provide.

Day length: Plants use water to provide the hydrogen molecule for photosynthesis, so it is understandable that longer days means more photosynthesis, and therefore more water used. Most plants are more active with longer day lengths and less active as the days get shorter, but not all. Some plants have adapted to be summer dormant in order to avoid drought stress, but the vast majority of garden plants are gearing up their metabolism in spring as the days get longer, and winding down in the fall when days are growing shorter. Plants also incorporate photoperiodism, a response where light receptors in the foliage activate specialized proteins which then impact gene expression, growth, and hormones. These light-activated proteins also regulate the opening and closing of gas-exchange pores called stomata. Photoperiodism is the mechanism for most plants’ ability to flower at the right time, go into and come out of dormancy, and hold on to moisture.

Temperature and water: Hopefully with shorter days, the temperatures are simultaneously getting cooler. Longer nights and cooler nighttime temperatures balance out the heat of warm sunny days. We intuitively understand that warmer temperatures evaporate water faster than cool temperatures, and evapotranspiration through a plant is increased just the same. If the weather stays warm into fall, your new plants need to pump more water through their leaves to keep up than if temperatures chilled out on time. On occasion, a rogue heatwave comes in the fall and can stress your newly planted fall garden, so keep an eye on the forecast in case they need a little support. Soil temperatures will lag behind air temperature; it takes more time for soils to cool down and warm up with the seasons. The soil will be cooler the deeper down you go, but new plants haven’t had the chance yet to grow their roots down far enough for that to be much help yet.

Wind: If you have a windy spot, wind can dehydrate, so a plant in a windy spot would lose little more water than the same plant in an otherwise-equivalent-but-wind-sheltered location, regardless of season.

Dormancy: Plants that are dormant need less water. Deciduous plants that are shedding those photosynthesizing leaves perform less photosynthesis, experience less evapotranspiration, and have a reduced need for water. Dormant plants still have metabolism functions and need to stay hydrated, but require much less water than when the leaves are being pushed out in the spring and running the show through summer. Even in dormancy, plants are still growing their root system, following where they’re rewarded with water, oxygen, and nutrients. Plants grow their roots year-round, with most growth happening in spring and summer with another little push in the fall. It makes sense that the most active season for a plant above ground would also be the most active growth season below.

Transplant stress: When installing plants out of a container, the roots that have supported that plant are still in the soil they’ve been growing in. In contrast, bare root plants are dug up during dormancy and all the soil is removed. They lose much of their root system in the process, and will need to overcome those losses in addition to getting established. Balled and burlapped (B&B) plants are grown in the ground until they’re sold, then dug up with up to 98 percent of their previous root system left behind. Unlike bare root plants where all the soil is removed, the soil that is excavated with the small rootball on B&B plants is kept and swaddled in burlap for transporting. Like bare root plants, they also have to overcome losses to their root system while getting established before they have enough mass to support the rest of the plant. While the pots that containerized plants are grown in can feel like we are adding to the waste stream with stacks of unrecyclable containers, those containerized plants are more forgiving if we don’t get them in the ground immediately.

Sourcing challenges: It is easier to go plant shopping when everything is actively growing, blooming, and looking so inspiring. Nurseries know this and will stock their shelves with whatever looks good, but if you can find the plants you want in the fall or arrange to purchase them then, you can take advantage of these seasonal assists. Having said that, I would not wait to buy plants if they’re only going to become root bound at the nursery waiting for you. Better to get them when they’re available and avoid plants that have endured a season of stress or have outgrown their container. To get around this challenge, have your wish list ready and talk to your nursery about when those plants are available and if they can be ordered for fall planting.