A warm and sunny spring afternoon can make it feel like winter is well and truly behind us - but here at Cedar Nursery, we know from experience that this is often when gardeners are at their most vulnerable. Clear skies and bright sunshine are actually the conditions most likely to bring a sharp overnight frost. And that combination of hope and cold reality catches even experienced gardeners out, year after year.
Why Sunny Spring Days Are the Sneakiest Frost Risk
There is a simple piece of science behind this, and once you understand it, you will never look at a clear spring evening quite the same way again.
Cloud cover acts like a blanket over the garden. It traps the warmth that has built up during the day and holds it close to the ground overnight. When skies are clear, that warmth radiates away rapidly once the sun goes down. Add a calm, still night with no wind to mix the air, and temperatures can drop surprisingly quickly - far lower than the daytime high would suggest.
"When I see a beautiful clear spring evening, I always think about which of my plants might need a little extra care overnight. The prettier the sunset, the more suspicious I get." - Dave, Nursery Manager
Here in Surrey and the wider South East, sharp temperature swings can persist well into late spring. The risk of overnight frost lingers longer than most gardeners expect, and it pays to stay alert rather than assume the season has turned for good.
Plants Most Vulnerable to a Late Spring Frost
Knowing which plants to watch is half the battle. These are the ones that need your attention on a cold spring night:
- Dahlias - newly planted tubers and emerging shoots are extremely frost-sensitive. Even a light frost can blacken and damage new growth significantly.
- Courgettes, cucumbers, and French beans - seedlings raised indoors and recently transplanted outdoors are particularly susceptible. They have had a sheltered start and simply are not ready for a cold snap.
- Tomato plants - a single frosty night can set back a young tomato transplant considerably. They are worth protecting every time frost is forecast.
- Tender bedding plants - petunias, pelargoniums, begonias, and busy lizzies should not be planted out until frost risk has genuinely passed. Patience here saves real heartache.
- Fuchsias - especially young or newly purchased plants that have not yet hardened off properly.
- Basil and tender herbs - basil is extraordinarily cold-sensitive and will suffer even at temperatures just a degree or two above freezing. Keep it under cover until nights are reliably mild.
- Newly planted perennials - even hardy varieties can struggle if planted during a cold snap before they have established any root system.
- Camellia and magnolia flowers - the plants themselves are hardy, but the flowers are frost-tender. Early morning sun after a frost causes rapid thawing that can damage blooms severely, which is why a north or west-facing aspect often suits them better than a south-facing wall.
The Good News - Plants That Bounce Back Beautifully
If you have woken up to a frosty morning and your heart has sunk, take a breath. Many plants are considerably tougher than they look.
"Don't panic if you wake up to a frosty morning. Many plants are tougher than they look, and with a little patience, they will come back stronger than ever. The garden is more resilient than we sometimes give it credit for." - Dave, Nursery Manager
- Hardy spring bulbs - tulips, daffodils, and alliums may have their foliage nipped, but the bulb itself is rarely damaged. Drooping leaves usually recover within a day or two as temperatures rise.
- Established hardy perennials - hostas, hardy geraniums, and lupins may show some frost damage on new growth, but they will push through fresh shoots once conditions improve.
- Brassicas and leafy vegetables - kale, cabbage, and Brussels sprouts are remarkably frost-tolerant and often taste better after a cold snap has sweetened them.
- Hardy herbs - rosemary, thyme, and chives handle frost well once they are properly established.
- Roses - established roses are generally resilient. New growth may be nipped, but the plant will recover and produce fresh shoots.
- Ornamental grasses - established clumps handle cold snaps well and rarely need any intervention.
Frost damage can look alarming - blackened, wilted foliage is genuinely distressing to see first thing in the morning. But in many cases the damage is superficial. Resist the urge to cut back immediately. Wait until temperatures have stabilised before assessing what has truly been lost. You may be pleasantly surprised.
Dave's Practical Tips for Protecting Your Plants Overnight
A little preparation before sunset can make a significant difference. Here is what Dave recommends:
- Horticultural fleece - keep a roll to hand throughout spring. Drape it over vulnerable plants before sunset and remove it in the morning once temperatures have risen. Even a single layer provides meaningful protection.
- Cloches and cold frames - ideal for protecting seedlings and young vegetable plants. A cold frame also allows you to harden off plants gradually rather than exposing them directly to outdoor conditions overnight.
- Mulching - a generous layer of mulch around the base of tender plants helps insulate roots from temperature drops. It is one of the simplest and most effective things you can do.
- Container plants - move pots into a greenhouse, porch, or even a garage overnight if frost is forecast. The thermal mass of surrounding walls provides meaningful protection that fleece alone cannot match.
- Avoid frost pockets - low-lying areas of the garden where cold air collects are the most vulnerable spots. Assess your garden's microclimates before deciding where to site tender plants permanently.
- Check the forecast every evening - make it a habit during spring. A clear, calm evening with temperatures dropping towards 4°C or below warrants action for vulnerable plants.
- Harden off properly - plants raised indoors or in a greenhouse need a gradual transition to outdoor conditions over one to two weeks before being left out overnight without protection.
When Is It Safe to Stop Worrying About Frost in Surrey?
This is the question we get asked most often at the nursery in spring, and the honest answer is that there is no single date we can give you. The last frost date varies from year to year, and a sharp cold snap can occur later than anyone expects.
In Surrey and the South East, the risk of ground frost typically eases as late spring moves towards early summer - but typically is doing a lot of work in that sentence. We have seen damaging frosts here in Cobham well into what should be mild spring weather.
"At Cedar Nursery, we always say: wait until you have had two or three weeks of consistently mild nights before you fully commit your tender plants to the garden. A little patience now saves a lot of heartache later. The plants will catch up quickly once conditions are right." - Dave, Nursery Manager
Frequently Asked Questions
How do I know if my plants have been frost damaged?
Frost-damaged plants typically show blackened, mushy, or wilted foliage, particularly on new growth and flower buds. The damage is usually most visible once the plant has warmed up in the morning sun. Do not cut back immediately - wait until temperatures are stable to assess what has truly been lost. You may find the damage is less severe than it first appears.
Can I leave horticultural fleece on my plants all day?
It is best to remove fleece during the day to allow air circulation, light, and pollination. Fleece is designed as an overnight protection measure rather than a permanent cover. Leaving it on during warm days can cause overheating and may encourage disease.
My tulips have been frosted - are they ruined?
In most cases, no. Hardy spring bulbs like tulips can look alarming after a frost, with drooping or blackened foliage, but the bulb itself is usually unharmed. Give the plant time and warmth, and it will typically recover well without any intervention needed.
Should I bring my patio pots inside every time frost is forecast?
For tender plants such as pelargoniums, fuchsias, and citrus, yes - moving them into a frost-free space overnight is well worth the effort. For hardy container plants, a layer of horticultural fleece or bubble wrap around the pot is usually sufficient to protect the roots from freezing.
What temperature should I start worrying about frost?
As a general guide, when overnight temperatures are forecast to drop to around 4°C or below - particularly on clear, calm nights - it is wise to take precautions for vulnerable plants. Ground frost can occur at slightly higher air temperatures than this, so it is better to act a little early than to regret leaving things to chance.
If you are ever unsure, come and talk to us. Our team at the nursery in Cobham - less than 5 miles from RHS Wisley - are happy to give you an honest read on current conditions and what we are doing with our own stock. Browse our full plant collection or use the Plant Finder at landscaping.co.uk to explore what might suit your garden - and don't hesitate to call us on 01932 862473 or visit us in Cobham, Monday to Saturday, 8:30am - 5pm.