seed planting and propagation
seedling propagation
styrofoam seedling propagation boxes
The styrofoam seedling propagation box is the easiest way for home gardeners to grow their own seedlings.  This page looks at the relative advantages and disadvantages of using this type of propagation box.  For details of how to make your own styrofoam propagation box see How to Make a Styrofoam Seedling Propagation Box.

advantages

Good moisture retention
Seedlings in styrofoam seedling boxes are grown on a base of several litres in volume of compost or garden soil, which means that when you water your seedlings the soil base below acts as a sponge and absorbs water for your seedlings to draw upon. 

This means that you don't have to water as often and there is a much greater margin of error should you forget to water your seedlings.

Lower risk of overheating
Illustration of a styrofoam propagation box showing how excess heat is vented out of the sides.
On a hot day excess heat easily vents out the side of a glass covered styrofoam propagation box, making it very difficult to overheat your seedlings.

Illustration of styrofoam box showing it's good insulating properties.
Because of the insulating properties of styrofoam the propagation mix in the styrofoam box will retain more heat at night.
The undulating top of the styrofoam box means that when a pane of glass is placed on top of it there are plenty of side vent holes.  If you unexpectedly strike a hot day and you haven't removed the glass top then the seedlings are unlikely to overheat as the excess heat easily vents out these side holes.

More stable temperature at night
Because styrofoam has good insulating properties and there is plenty of mass in the form of the soil/compost base styrofoam propagation boxes retain more heat at night than commercial propagation boxes.  This means that your seedlings will grow quicker and seeds that need higher soil temperatures, such as eggplant, basil and capsicum, to germinate are more likely survive.

inexpensive to make
A styrofoam propagation box costs little to make.  The boxes themselves can usually be picked up at supermarkets or green grocers for nothing and if you have some second hand glass all you will need to buy is a glass cutter.  Otherwise a sheet of glass can be bought from a glazier for around $11 AUD.  By contrast commercial propagation boxes sell for $25 to $30 AUD.

durable
As long as you don't break your glass a styrofoam seedling box will last for years  In contrast the plastic tops on commercial propagation boxes usually become brittle and crack after four or five years.



disadvantages

cant' be heated using artificial heating
The size and insulating properties of styrofoam boxes means you can' place them on a heating tray.

weed seeds can cause problems
While the seeds are germinated in a thin layer of sterilized seed raising or potting mix the base is made up of garden soil or compost which is not sterilised.  So any weed seeds in your compost or garden soil base are likely to also germinate.