Why plant on Saint Catherine’s Day? Key dates in the calendar of gardening saints

“On Saint Catherine’s Day, every tree takes root.” This is the best-known saying in the gardeners’ calendar, and one of the few whose agronomic basis is perfectly sound.

Behind the saying lies a simple rule: autumn is by far the best planting season for almost everything perennial. Here’s why, and what it changes in practical terms.

Why autumn, really

Three mechanisms work together, and each one matters.

The plant no longer spends anything above ground

In autumn, the above-ground part enters dormancy: no more leaves to feed, no more growth to support. All available energy goes to the roots. A plant put in the ground at this time devotes all its resources to establishing itself, instead of dividing them between leaf growth and root development.

The soil is still warm and becomes moist

This is the decisive combination, and it lasts only a few weeks. In October and November, the soil retains the heat accumulated during summer — often 12 to 14 °C — while the rains return. Yet roots continue to grow as long as the soil remains above approximately 5 °C, even when the plant appears dormant.

In spring, the opposite is true: the soil is cold and warms slowly, while the air is already pushing the plant to break bud. It produces leaves before it has the roots to support them.

The first summer is determined by the previous autumn

This is the most important practical consequence. A plant installed in October has eight months of root development before its first drought. One planted in April has only two, and faces July with a shallow root system.

In practical terms: a hedge planted in autumn will need one or two emergency waterings the following summer; the same hedge planted in spring will need watering all summer, and will still lose some plants.

This also explains the second, less well-known saying: “Whoever plants during Advent gains a year’s head start.” This is not just a figure of speech — it is roughly the actual difference in development between autumn and spring planting, measured after three years.

What to plant in autumn

What not to plant in autumn: anything that is susceptible to frost and does not have time to establish itself — Mediterranean species in cold regions, and plants with fleshy roots that are sensitive to excess winter moisture in heavy soil. In very clayey, poorly drained soil, it is sometimes better to wait until spring.

How to plant correctly

1. Wide rather than deep hole — two to three times the width of the root ball, but no deeper than it. During the first year, roots spread laterally far more than they grow downward.
2. Scratch the sides of the hole. A hole dug with a spade in clay soil develops a smooth surface that roots cannot penetrate — the plant remains trapped in its hole like a plant in a pot.
3. Loosen the root ball if the roots are circling. For a container-grown plant, this is essential: otherwise, they will continue spiraling and eventually strangle the tree.
4. No fertilizer at the bottom of the hole. It is counterproductive: the roots have no reason to grow out and explore if everything is within reach. Mature compost mixed with the backfill soil is sufficient.
5. Keep the root collar at the right level — the junction between the roots and trunk must remain level with the soil. If buried, it rots; if exposed, the roots dry out. This is the most common and most fatal mistake.
6. Water thoroughly, even in the rain. This is not to hydrate the plant, but to make the soil adhere to the roots and drive out air pockets.
7. Mulch to a depth of 10 cm, leaving a few centimeters clear around the root collar.
8. Stake only when necessary, keeping the support low and flexible. A tree that moves slightly develops a stronger trunk.

The other dates in the saints' calendar

St. Catherine's Day is not the only one. Here are a few markers that have endured through the centuries, along with what they are really worth:

• The Ice Saints, May 11–13 — Mamertus, Pancras, and Servatius. Their statistical basis is debated, but the principle remains valid: do not put frost-sensitive plants outside before mid-May in most regions.
• St. Vincent's Day, January 22 — the start of grapevine pruning, before the sap rises. The principle applies to all fruit trees: prune while dormant.
• St. Joseph's Day, March 19 — a marker for the beginning of spring; carrot sowing time in some regions.
• St. Michael's Day, September 29 — the end of the summer harvest and the beginning of autumn soil preparation.

The complete collection, month by month and including regional origins, is in The complete calendar of gardeners' sayings.

These dates are not scientific: they are fixed calendar markers in a climate that is not. Their value is mnemonic—they remind us that something needs to be done during this period. The right action, however, is decided by looking at the soil and the weather.

Mistakes when planting in autumn

1. Planting in waterlogged soil. Wait until it has drained. Waterlogged soil that is worked compacts and suffocates the roots for years.
2. Planting when the ground is frozen. If the soil is frozen, wait. Bare-root plants can be stored for a few days in a temporary trench—laid on their sides in sand or loose soil.
3. Burying the crown. The most fatal—and most common—mistake.
4. Pruning after planting. Except for bare-root plants, where light trimming balances the plant, leave it undisturbed during the first year.
5. Forgetting to water during a dry autumn. An autumn without rain does happen, and a recent planting will not survive six weeks without water.

Frequently asked questions

How late can you plant?

As long as the soil is neither frozen nor waterlogged, the planting window for bare-root plants runs from November to March. The best results are still achieved in November and December.

Bare-root or container-grown?

Bare-root plants cost significantly less, establish very well, and often root better—their roots have never spiraled. The only constraint is that they can be planted only during dormancy and must never dry out between purchase and planting.

Should you water in winter?

Rarely, except during an unusually dry autumn or winter. Water generously when planting, add mulch, and let the rain do the rest.

What if I miss the autumn window?

Plant in spring, but early—March rather than May—and plan to water throughout the first summer. The result will be satisfactory, simply with a year’s delay in growth.

Does the saying apply everywhere in France?

The principle is right, but not the date. In the Mediterranean region, the window is wider and autumn is definitely preferable. In the mountains, where the soil freezes early, it is better to plant as early as October—or wait until spring.

Key takeaway

The saying is true, and for good reason: in autumn, the plant no longer invests energy above ground, the soil is still warm, and winter gives it eight months to establish roots before its first dry spell. Plant wide and not deep, keep the crown at soil level, water to settle the soil—and let nature take its course.

To learn more

• The complete gardener's proverb calendar, month by month
• Autumn vegetable garden: what to sow and when to harvest?
• Why sow edible perennials?
• Drought-resistant plants

For your autumn planting: our autumn seeds, our perennials, and our trees and shrubs.