When to water a sheetmulched bed?

So realising that time was slipping away from me, and I had been procrastinating instead of gardening.

Yesterday I thought I'd put in a sheetmulched bed, as shown in Geoff Lawton's 'Soils' DVD. Fortunately, being a farmer, I have plenty of large round hay bales, so I used one of the older dumpier looking ones for this project. I soaked the cardboard, and the layers of hay as I went, so there's a fair bit of moisture in it at the moment. My question is, how do I decide when to water it?

That would probably depend on what you plant. You can always pull back the mulch to check the soil moisture. Otherwise I would advise watering well until germination and then tapering off thus training your plants to look for their own water. They will develop a deeper root system with infrequent deep watering versus frequent shallow watering.

I have planted seedlings, so the they are germinated already.

Are the seedlings planted through the card into the native soil, or on top? If the latter, they dry out really quickly.
One way or another, I find transplanted seedlings need regular watering (like every couple of days), until they're settled in.
I'd only water the actual plants: the sheetmulch should do a good job of maintaining moisture in the soil, and in my experience, it will only really start to break down when the autumn rains come.

Thanks Leila. The mulch was damp about two or three inches down, and that's about how far the soil level is for the plants. There is problably 8-10" of store-bought compost/potting soil above the cardboard (in 4-6" diameter "tubes" I burrowed through the mulch.. The soil under the cardboard isn't terrible, but was suffering from being bare through the heat of summer.