The spell druid grove (XGtE, pg. 154) lists several effects that the caster may impose on the spell's area (30-90 ft. cube). The spell also comes with an "Additional Spell Effect"; this reads:
You can place your choice of one of the following magical effects within the warded area:
So you select one of these spell effects and choose the location of its point of origin within the druid grove area.
The each spell's listed area of effect can easily extend beyond the boundaries of the druid grove, especially if you only create a 30 foot cube grove.
Can the area of effect of the additional spell effect extend beyond the boundaries of the grove, or does the grove restrict the spell's listed area?
As an example see this diagram. Here we have a 30 by 30 foot druid grove, and a 20 foot radius spike growth centered at the center of the grove:
Does such an arrangement work? Or must the spike growth be confined to the 30 x 30 foot area of the grove?