When is the Best Time to Plant Perennials UK?
Mid-Spring and early Autumn are best. Summer is fine, especially in the shade. Winter often leads to plant failures or setbacks.
Autumn and Spring are both ideal for planting perennial plants, allowing for strong root development and healthy growth.
Dates will be earlier in the South West, later in cold Northern & Scottish regions.
Early Autumn (September-October)
- Warm soil promotes root establishment before Winter
- Those new roots can take advantage of warm spells
- Strong spring growth results
Spring to early Summer, (late April-June)
- After frost, as the soil warms to about 10C,
Midsummer (July-August)
- In Shade: Fine
- In Full Sun: With careful watering, possibly shade cloth, usually fine, just don’t plant in a heatwave
- Avoid over or under-watering
Winter (November-March)
- Generally avoid planting herbaceous perennials
- Risk of rot or stunted spring growth
- Better to overwinter in their pots in shelter, plant in Spring
- On the other hand, Winter is bareroot planting season for woody perennials like trees, roses, and hedging
What is a half-hardy perennial plant?
These plants tolerate light frost, and generally survive outdoors with winter frost protection like mulch. A prolonged deep freeze is likely to kill them.
Most perennials we grow are fully hardy and live outdoors year round across the UK.
A tender perennial will not survive even a breath of frost, so either it can be brought inside for winter (like Dahlia tubers often are), or moved to shelter if grown in a pot.
A half-hardy perennial (HHP) is sort of a fake, in-betweener category caused by growing plants from warm countries in the cooler UK climate: Pelargoniums and Fuchsias are common examples.
It’s not a fixed category, because it depends on your local conditions and the microclimate where it grows: in the warm South-West of England and Wales, some tender perennials “become” half-hardy.
They can withstand a light frost, and will generally survive outdoors in winter with good frost protection such as a pile of straw, mulch, or horticultural fleece, but a prolonged deep freeze may still be too much.
Dry soils are typically best for overwintering half-hardy perennials.
Tips for First-Time Perennial Planters
- Know your soil type, pH, how much light the exact planting site gets in Spring-Summer, and how wet it gets in Winter.
- Choose “right plants, right place”, rather than thinking about big changes to the site.
- If plants you like aren’t suitable, search for alternatives, which may be a combo to get the desired leaves and foliage.
- Space plants according to their mature size, some like a bit of legroom.
- Water thoroughly after planting.
- Mulch retains moisture and suppress weeds.
- Label plants or make a real scale map.
- Be patient, perennials often take a year to establish and flower properly.