01 / Look at what you have
A new tray is
not the first requirement.
University of Maryland Extension says clean containers with good drainage and a depth of at least two inches can work for starting seeds indoors. Check what you already have before building a shopping list.
A purpose-made tray may help organize your layout. Its cell count alone does not tell you whether it suits your growing space or routine.
Read the Extension container guidance ↗02 / Make a path for water
A growing container.
A water-catching tray.
Two different jobs.
Drainage holes allow water to leave the growing container. An undrained flat beneath it catches water; it does not provide drainage on its own.
Check the container and the tray underneath it as a complete setup.
Maryland Extension cautions against overwatering when using flats without drainage holes. Keep that distinction in mind when comparing inserts, modules, and supporting trays.
Read the drainage guidance ↗03 / Plan the growing space
Think beyond
the windowsill.
University of Maryland Extension notes that window light is rarely enough for indoor seedlings. Plan your light source alongside your containers, rather than assuming a bright-looking window will be sufficient.
Measure the usable area under your light and inside your supporting tray. Outside dimensions determine physical fit; published cell measurements describe the compartments.
For crop-specific timing and indoor light guidance, consult the full Extension guide and the instructions for your seeds.
Explore the indoor seed-starting guide ↗