For example, ask the children to fill several plant pots with potting compost and plant seeds or cuttings. Water them and place transparent, colourless plastic bottles which you have cut in half over some of the pots to form mini greenhouses. Explain to the children why you are going to cover some of the pots and leave others uncovered. Otherwise treat all the pots the same: give them the same quantities of water and keep them in the same place, so that they get the same amount of light and heat. Every day observe what has happened to the plants and to the plastic bottles. As an extension activity the children could measure the temperature in the plastic bottles and in the room.
Afterwards talk with the children about which plants have grown the fastest and why that might be. Talk about how plants need warmth to grow and that they grow more rapidly in a warm atmosphere. The plastic bottles have a film of condensation on the inside which helps to keep the plants moist.
Further details about this activity can be found here.
This is just one activity out of many in Gardening: Activities for 3 – 5 year olds, published by Brilliant Publications.
For more information or to order Gardening: Activities for 3 – 5 year old for just £6.50, visit https://www.brilliantpublications.co.uk/book/gardening-102