The Best Time of Year to Plant in Raleigh (USDA Zone 8a)

You have likely heard it already; fall is for planting. But before we delve into the advantages of planting in the autumn let’s describe the situation for a newly planted plant.

When plants are grown in the nursery the most common growing media consists almost entirely of aged pine bark fines, usually lime and sand are added as well. Sometimes more specialty greenhouse growers will use a blend of perlite and peatmoss.  These potting mixes are very well drained, providing excellent levels of oxygen to the roots, as well as being very high in organic matter. The mixes usually have a top dressing of slow-release fertilizers that leach nutrients every time they are irrigated. The irrigation of most nurseries is monitored very closely. Nursery plants are fully watered whenever the growing media is around 80% dry, which is perfect for a majority of garden plants.

When a plant is removed from the nursery environment, taken from its pot, the soil is partly shaken out and it is planted into what is likely a clay soil found here in the Triangle. Now the plant has the root system the size of the pot it was in, mostly wrapped in a quickly draining mix surrounded by chunks of heavy mineral clay soil it is not encouraged to reach into.

Nursery growing media (left) beside loamy clay soil (right)

In spring and summer, plants are less focused on growing out their root system as they are on growing their tops i.e., their stems leaves and flowers. Also, the weather is hot and humid. For full sun plants without establishing deep roots adapting to new soil is stressful in the drying sun. For shade plants, the trees that give them shelter are also competing for water as their canopies bake in our 90-degree Fahrenheit plus average temperatures. All the while these newly planted plants have a root system the meager width and depth of their nursery pot and haven’t adjusted to the drastically different soil type around them.

Planting into the growing season is completely fine if you can water like a professional nursery, monitoring moisture and fully saturating the plants, and the surrounding areas; which is important because dry soil will wick water away. Although we get more rain than many other areas in the country, this is rarely going to be enough to maintain adequate water needs when the plant still has its nursery pot sized root system. With watering new plantings, timing is of the upmost importance because you also want to avoid over saturating the plants to the point that they are unable to get sufficient oxygen. With consistent saturation, root rot can set in.

Freshly planted bed with irrigation tubing connected to an automatic timer (not shown) to ensure adequate watering.

Let’s now examine planting in the fall. In later stages of the growing season, for most plants, when the flowering is done, the seeds have been set, and future dormancy looms in the not-so-distant horizon with the slowly approaching winter. Many plants direct what energy they have to growing out their root system this time of year. However, what is most important, they don’t have the water demanding heat of the summer time to contend with. Also, most of our plants here go dormant through the winter so regardless, they barely need water at all because they aren’t transpiring it from their leaves.

When spring blooms again and warmer weather soon follows, plants planted in the fall have already had some adaption to the new soil. If they haven’t set deeper roots already, they are far more prepared as they grow through the spring, and yes, not to be confusing but plants grow their roots through the hot growing season too.

Freshly planted perennials (Penstemon) in October. Summer interest plants still blooming late into the season.

Don’t be fooled by a broad commercial definition of the seasons or definitive dates associated with solstices and equinoxes. Nature’s perspective shows us when the seasons actually occur where we live. For example, despite “fall themed decorations” September is reliably a late summer month here in the Triangle. The seasons vary widely by climate and weather, year by year. In Raleigh our average seasons from a horticultural point of view usually look something like this:

Winter (Great time to plant): Late December – February

Spring (Challenging time to plant): March – Early May

Summer (Worst time to plant): Mid May – Early September

Fall (Best time to plant): Mid September – Mid December

Of course, anytime is excellent to plant if you water correctly and diligently. You’ll just have more forgiving results when you forget to water during a ten day stretch of no rain in the summer. Generally, our retired clients are exclusively capable of watering reliably but even this is a toss-up. The need for correctly watering in the first year to 18 months after planting is a major selling point for expensive irrigation systems, simple automatic irrigation timers, and garden maintenance contracts.

We’ll conclude with a quote that will stick with me forever from local horticulturalist and Star Roses Representative, Guy Hartsell: “I only plant in my own landscape the first week of November. That way I only have to water once, the day I put the plant in the ground. I find out at the end of next summer whether it’s going to make it or not. I’d rather rip out a dead plant and try something else then drag a darn hose around all year.”

While Guy takes a fair approach, we still recommend diligent and correct watering, especially the following summer for any new plantings.