Gardeners urged never to do these 5 things during a false fall – or risk permanent damage to plants

The air is beginning to cool, and leaves have started to fade to yellow in the garden, but don’t be fooled into thinking fall has arrived.

Rushing out to get everything done on our fall gardening checklists will feel tempting for many of us, but across the country many gardeners are experiencing what’s known as a false fall. This is a temporary drop in temperatures before the mercury rises again, and is confusing to both plants and gardeners alike.

As such, there are certain tasks which must always be avoided during this period, or you will risk doing severe damage to plants and trees.

False or official fall?

A false fall is, in fact, a stress response to temperature fluctuations, and is not a signal that fall has arrived. This year, fall officially begins on Monday 22nd September.

These are the 5 things never to do during a false fall.

Pruning

It’s really tempting to get the pruning shears out when cooler weather arrives, especially if shrubs or roses look straggly and foliage is turning brown. But pruning during a false fall is risky. It stimulates a flush of soft new growth, which won’t have time to harden off before frost hits.

'It is risky to do a lot of pruning during a false fall, as any trimming will trigger the plant into putting on fresh, new growth,' affirms Says Drew Swainston, gardens content editor at Homes & Gardens.

'Any pruning, coupled with the temperatures increasing for a few weeks before true fall arrives, will signal the plant to produce new stems quickly. This lush growth, as a result of the pruning, will not have time to harden off before the first frosts and temperatures drop for winter.

'When these stems get damaged by cold, it increases the plant’s overall susceptibility to pests and diseases. It is much more beneficial to leave pruning until the correct time of year, which is usually late winter or early spring for most deciduous trees or shrubs. Ensure your plants are sufficiently watered during a false fall, but leave the pruning tools in the shed.'

Instead: Focus on removing only dead, diseased, or damaged branches. Save reshaping or hard pruning for later in the winter or very early spring, when plants are fully dormant and can regrow strongly.

There are certain plants to prune in September, which we detail in our dedicated guide.

Clearing leaves

A false fall often brings an early leaf drop, especially from stressed trees, and it’s tempting to get the leaf blower or rake out and sweep everything away.

But if you clear too soon, you’ll likely be repeating the job over and over again when the real fall sets in.

Plus, a thin layer of fallen leaves can actually insulate soil and provide shelter for beneficial insects and pollinators. Removing them prematurely robs wildlife of habitat and leaves bare soil exposed to late-season sun and dryness.

Instead: You can sweep and tidy paths, patios, and lawns to prevent slippery surfaces and smothering, but let leaves remain in borders and under shrubs until leaf drop is truly over. At that point, you can gather them for leaf mold or compost, or leave some in place as natural mulch.

Fertilizing

A false fall can trick people into feeding plants for the winter. But, similar to with pruning to early, fertilizing now encourages tender new growth that may be damaged once real fall and frost arrive.

Fertilizer, especially anything nitrogen-rich, encourages lush, leafy growth that won’t have time to mature before true cold sets in. Instead of strengthening plants for winter, it leaves them soft and susceptible to frost injury.

Instead: Hold off on fertilizer until late fall. At that point, you can add compost or use a low-nitrogen, high-phosphorus fertilizer to boost root health.

Dividing perennials

Dividing crowded perennials or relocating plants is a classic fall job, but timing is everything.

This is best done once cooler weather is consistent. Doing it during a false fall can leave stressed roots exposed to renewed late-summer heat.

If transplanted now, plants could wilt, fail to re-establish, or even die when heat returns. Waiting until consistent cooler days arrive gives them the chance to settle in, grow strong roots, and head into winter in better shape.

Instead: Wait until temperatures have truly cooled and remain steady. Then divide or transplant so roots have several weeks to establish before the ground freezes. If you must divide early, keep divisions well-watered and shaded until the heat has passed.

Reduce watering

Lawns, containers, and perennials still need consistent moisture. If you assume the fall weather is here for good and cut back on the watering too soon, this could stress plants when the heat comes back.

That little taste of cool weather can trick gardeners into thinking plants don’t need as much water, but soil temperatures are still high, and plants are often still actively growing or fruiting. Container plants in particular dry out quickly if warm days return.

Instead: Keep watering consistently, especially vegetables, lawns, and containers. As true fall arrives, you can start watering more deeply but less frequently, which encourages strong root systems ahead of winter.

As with so many wonderful gardening tasks, timing is crucial to ensure the health of your plants and to make sure you get the best out of them during the following season. There are lots of other jobs you can begin in fall, such as attracting wildlife to your garden and giving the ecosystem a boost, even as the temperatures drop.

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