Around here (Boston) the spring rains are generally fairly light to
moderate, so plant now. The rain will help to water in the seeds and
start them germinating.

If we were going to have a really heavy rain the seeds might wash out.
Look out for "thunderstorms" as keywords in the weather forecast.
Generally more of a problem later in the summer.

If they wash out, just plant them again. It's still early enough. Seeds
are fairly cheap. The arugula and beets (and many other common garden
veggies) you should plan on doing a second or even third planting later
in the year anyway (2-4 week intervals). If you like your beets really
big, just plant a lot now. If you like beet leaves, do several plantings
so you have a more consistent supply of small tender leaves. My arugula
tends to go to seed after a while, so I do several plantings so there
are always some young plants to chose from.


Laura J wrote:
... We're supposed to get rain pretty much all
week. If I plant the seeds now, are they going to wash away? Is it better
to plant before or after a rainstorm? It's a raised bed garden with peat
moss, compost and a little vermiculite so it should have good drainage...