Plant peas in your garden when the daffodils bloom.
Plant tender plants in your garden when the lilacs are in full bloom.
I grew up hearing these phrases from my Grandfather and then my Mother and always followed this advice, with great success.
Although it’s basically an old wives tale, there’s actually a science devoted to studying how cues from nature can tell us when to plant, harvest and when to watch out for insect invaders. It’s called phenology and it’s based on the fact that even tiny changes in climate can affect plants, insects, etc. and their behaviour. Long ago our ancestors would have noticed that there isn’t usually a frost after the lilac blooms so it’s safe to plant out tomatoes, peppers and other warm weather crops.
Phenology is a very old science and has been useful in showing the general trend of global warming. For instance, records of the exact date of the pinot noir grape harvest in Burgundy have been kept for over 500 years and so meteorologists were able to very accurately track temperature trends during spring-summer-fall for those times before we had instrumentation (like thermometers!) A more advanced science of phenology using weather satellites in orbit around the earth which pick up tiny changes in climate over whole ecosystems is now commonly used to track changes in the weather resulting from global warming.
This year, however, my own gardening efforts will have to be limited to a cherry tomato plant and a few herbs in a pot due to the house sale and build. Next year, however – a BIG garden, I hope!