Why Fall and Winter Planting Makes Sense
You've probably heard that fall is the best time to plant. But why, exactly? Sure, the weather's more comfortable and you're not battling summer heat. But there's a deeper reason—one that has to do with how plants make decisions about where to send their energy. Understanding this helps explain why plants installed from fall through late winter establish more easily than spring plantings, and why winter planting actually works despite the cold weather.
Energy Allocation Within Plants
Plants use carbohydrates from photosynthesis or stored reserves to fuel maintenance, stress response, and growth. Like a household budget, they have limited resources and must make tradeoffs. Beyond deciding which processes to fund, they must choose where to send resources: roots, stems, leaves, or flowers. This is called source-sink dynamics in plant science—think of it as an energy tug-of-war where whoever's growing fastest gets fed first.
Not all plant parts demand resources equally. Areas of rapid growth—like buds that explode into new branches and leaves in spring—exert much stronger demand than slow-growing roots. This is similar to the dinner table food allocation between a hungry teenager and an aging grandparent.
Importance of Root Growth For Newly Installed Plants
So what does this mean when installing a new garden? Plants grown in nursery pots have been raised in artificial, coddled conditions with regular water and fertilizer. They haven't needed to develop extensive root systems to search out nutrients and water to support their lush top growth. At planting time, this results in the plant's root system being undersized relative to its top growth.
This root shortage is especially pronounced in trees and shrubs—woody plants that have spent 2-3 years in containers can have substantial top growth but roots constrained to a few gallons of soil. Herbaceous perennials have the same issue but on a smaller scale since they're typically younger with less top growth.
Once in the ground, the plant needs to focus on growing out its root system to correct the imbalance. This is a major reason why newly planted perennials, shrubs, and trees don't seem to do much the first year—they're busy building roots underground.
Impact of Timing of Planting on Growth
Spring Planting: Limited Root Growth
Spring plantings face two challenges. First, slow-growing roots must compete with fast-growing shoots for the plant's limited energy budget. Those explosive spring buds—the hungry teenager at the dinner table—overwhelm the slower-growing roots in the competition for carbohydrates.
Second, spring soil temperatures create a handicap. In spring, soil temperatures at root depth lag behind air temperatures by 2-4 weeks. When March air reaches the low 60s, soil at planting depth might still be in the mid-40s. Root growth slows when soil temperatures drop into the 40s, and is optimal once soil warms into the upper 50s and 60s. This means roots grow even more slowly than normal, weakening their ability to compete for the plant's limited energy budget.
Fall and Winter: When Roots Get Priority
Fall and winter plantings reverse this dynamic. As deciduous trees drop their leaves and herbaceous plants die back, top growth stops competing for resources. Roots become the priority—the plant can finally focus its energy budget on building the underground system it needs.
Temperature works in your favor too. In fall, soil stays warmer than air for weeks. When November air drops into the 40s, soil often remains in the 50s or low 60s—perfect for root growth while shoots stay dormant. In Charlotte's mild winters (zones 7b-8a), soil at planting depth rarely freezes, so roots can continue growing, albeit slowly, during warm spells even in January and February.
What This Means for Your Garden
For the best establishment, aim to install plants between mid-September and March when you can. This gives roots time to grow before summer heat arrives.
Relative to fall installed plantings, expect spring installed plantings to show greater moisture stress and need more frequent irrigation. The difference in irrigation needs is greater in trees and shrubs relative to herbaceous due to their greater root to shoot imbalance (longer life in pots) and lengthier establishment period.
When Spring Planting Makes Sense
Spring has real advantages. Plant availability is dramatically better and often higher quality, especially for native perennials that need cold stratification, late-season bloomers like Liatris and Joe Pye Weed, and warm-season grasses. Warm-season grasses (little bluestem, muhly grass) actually prefer spring planting once soil warms into the 70s. For many gardeners, spring is also when you actually have time to focus on the garden.
Both seasons work. Fall gives plants a head start on root growth. Spring requires more attention through summer but gets you to the same place. The key is understanding what each season requires so you can plan accordingly.
