7 plants to prune in September – this month may be your last chance for these before the window closes for the year

As summer turns to fall, the list of jobs to do in the garden often doesn’t feel like it gets any smaller. Understandably, some things do fall to the wayside, including pruning, but September can provide a final opportunity for pruning some plants. So, if you are like me and don’t like skipping the trimming altogether, the good news is that there is still time to get it done.

This pruning can keep plants healthy, looking neat and controlled, combat potential pest and disease problems, and help guarantee better yields. To me, that is the motivation to head out with the pruning tools, and, as the old saying goes, better late than never.

With that in mind, I highlight seven plants to prune in September that might really need some TLC in the coming days or weeks. If you haven’t done so already, head out and give them attention, and add these trimming tasks to your late summer gardening checklist.

Plants to prune in September: Part 2

This time last year, I highlighted some popular plants to prune in September, like summer raspberries, climbers such as jasmine, passionflower, and honeysuckles, as well as some hedging plants. But there is more worth knowing about, so who fancies a sequel? Let's start looking at seven more plants to prune in September.

1. Yew

Yew is very popular as both a hedging plant and a plant for topiary, but it does need regular attention to keep it looking at its best. That includes two trims a year, one in late spring or early summer and another in late summer or early fall.

September is an ideal time to trim yew as the heat of summer is past, and the shrub has a chance to recover before the temperatures really drop for winter. Pruning this month is more of a gentle trim rather than a heavy one – leave any renovation pruning for spring.

2. Iris

Exactly when you cut back irises may depend on your climate, but they need trimming after they have finished flowering and before the foliage completely flops. Once all the blooms have faded in late summer or early fall, remove the stems as close to the rhizome as possible.

This is important when growing irises as it prevents disease from moisture on the foliage, and reduces the risk of the iris borer pest that overwinters in old foliage and can cause the rhizome to rot.

3. Wisteria

This is a final reminder to prune wisteria.

The climber requires pruning twice a year, with the summer trim typically occurring in August. However, if you grow wisteria and have not got around to this, September is the final chance to do it, ideally before the middle of the month.

It is recommended not to forget about pruning wisteria twice a year, as the vines grow quickly and can get unruly if left unchecked.

And the summer prune is so simple, there is no excuse not to get it done. Simply identify all of this year’s growth, and cut the whippy shoots back to five or six buds.

4. Lavender

Again, this is a final reminder to prune lavender before the window closes for the year, which is essential if you want to avoid woody or leggy plants.

Ideally, it is done in August, but September is also OK, but the earlier you get to this task this month, the better.

You can cut back hard to shape the lavender shrub, but don’t trim into the old wood. That is a lavender growing mistake because the plant won’t resprout from old wood – stay safe and trim up to 2-3 inches above the woody base.

5. Tomatoes

This one isn’t necessarily essential, but it comes highly recommended when growing tomatoes. It may seem counterintuitive to prune tomato plants and stop them from growing, but there is method to the madness.

Topping tomato plants at the back end of the season helps your plants ripen existing fruits rather than put energy into producing new ones.

Without intervention, the rampant plants will continue to grow stems, leaves, and fruits. However, you’ll be left with lots of green tomatoes come the end of the season. You can ripen green tomatoes in a bag with a banana at home, but that should be a last resort. Ideally, the tomatoes naturally ripen on the plant.

Simply cut out the growing tip of the plant once it has developed enough trusses; usually, four or five trusses are sufficient. Doing this and thinning out foliage diverts the energy into ripening all the fruits it is currently growing. You’ll be harvesting tomatoes ripened to perfection in no time.

6. Blackberries

When you grow blackberries, they are productive, but vigorous plants. They need space and require pruning to keep them tidy and not too overzealous with their fast-growing arching stems.

You prune blackberries in the same way as summer-fruiting raspberries, and September is the perfect window to do this. The canes produce fruit on two-year-old canes, so trimming involves removing this year’s fruiting stems and leaving those that grew this year, which are often trained onto wires to keep the plant orderly.

While you can get thornless varieties of blackberries, most of the time you want a good pair of thornproof gardening gloves (like these long thornproof gloves at Amazon) to protect you from the plant’s sharp thorns.

7. Boxwood

Boxwood, whether grown as hedging or clipped into topiary, can be given a tidy-up in September. This late gentle trim maintains the shape and keeps the plant looking neat all winter long.

This month offers a good window to trim boxwood bushes. Doing so earlier than late summer/early fall risks the boxwood turning yellow from leaf scorch, and post-September risks the box being damaged by frosts.

Shop pruning tools

September also presents a great opportunity to propagate new plants for free by taking cuttings.

Our guide to plants to propagate in September reveals shrubs, perennials, and tender plants that are ideal for taking cuttings this month, along with some expert tips to help you expand your collection with confidence.