yes, once it is out in the sun i leave it there until i cut it.
The reason i do not fill the water tray before i put it out in the sun is because the soil would absorb the water and the sprouting seeds would not deveolp long roots as they dont have to go far to get some water.
If you let the seeds sprout in the dark, giving just a little bit of water each day to keep them moist they will develop long roots. you know when you have done this correctly as when the tray is ready to be put in the sun you can see roots coming out the bottom of the tray.i just put some newspaper over the tray, and when they lift up the paper put them in the sun.
once in the sun only water them via the water tray not from above as you would do if you covered the top with soil. the only time you water them from above is during sprouting when they are kept dark.
you will notice that the top remains quite dry but the wheatgrass gets all the water it needs from its roots. this has eliminated ALL my mold problems, and when you cut the grass you can cut them right down close to the base and not have to worry about juicing soil
NOTE - i said fill the water tray every 2 days, this is only a rough guide. when its hotter you can fill it more often, i usually water the trays then water again so there is still water in the tray. you will be surprised at how much water wheatgrass actually needs. remember to use clean filtered water!!!!
I also add 2 teaspoons of Sea Salt (proper) to the water when i first put the tray in the sun to ensure my wheatgrass is rich in minerals, as most soil is mineral depleted
---- The reason alot of people get mold growing on wheatgrass is because mold loves moist surfaces, when you cover the seeds with soil and water from above you are creating an ideal environment for mold to grow on (i.e wet soil). It is also important to rinse the seeds properly after they have been soaked.
----- If you find that your grass is growing slowly or is not very green you may need to use fertiliser, especially true if you are just using garden soil from your back yard. I only use organic fertiliser made from urine and water in a 1:10 dilution which i put in the water tray once a week for each tray. Urine is very high in nitrogen and many other benfical nutrients plants need for growth. Although this may sound strange it is practiced in many countries for organic farming