The instructions on the label of most fertilisers advise against use in frost conditions, you may have often wondered why we put this, and what would happen if you ignored the advice. I hope to answer these questions here…
What does the label say?
SmartLawn fertiliser labels advise against the application of product “if frost or drought conditions are expected to occur”, this is about avoiding application during times which are already quite stressful for a lawn. It is usually possible to know if frost will occur in the short-term but the forecast does not often stretch further than a few days. We advise waiting until all frost risk is gone, and the ground temperature is at least 5 degrees Celcius, before applying any fertiliser.
Why do we say this?
British lawns can cope well with frost if left alone and given time to recover. The freezing of water inside the grass blades does not cause damage as such but does cause the plant to be stressed as it is not able to access the water that it needs to live. The worst thing we can do to the lawn at this point is to cause even more stress.
Pretty much everything we do to lawns causes them stress; applying fertiliser is one of them. Fertiliser is naturally quite salty, we can scorch lawns any time of year with it quite easily by applying too much in one go. In frosty conditions the water is already locked up as ice and unavailable to the plant, the salty fertiliser we apply draws even more moisture out of the roots causing harm and a lot of stress to the lawn.
Another reason not to add fertiliser in frosty conditions is the risk of soft growth. Some spring fertilisers are high in nitrogen and applying them in very cold periods can force the grass to grow even though it is not healthy to do so. Fungal diseases can become a problem for grass plants who have exhausted their energy growing leaves that they did not need.
What else is there to bear in mind?
You should discourage your customers from walking on their frosty lawns as this will cause damage to the leaves. The damage will be slow to heal due to low temperatures and footprints may be visible for days or weeks afterwards. Of course, if your customers should not walk on a frosty lawn then you should definitely not be walking on them yourself with a fertiliser spreader.
It may be obvious but we also do not recommend applying fertiliser to lawns covered in snow. It is best to wait until the snow has melted and the grass blades are standing back upright again before you work on the lawn again. Walking on snowy lawns should be avoided but households will children will find this very difficult to avoid!