Keep in mind when planting that Grovemount Blue is thought of as hardy, so Grovemount Blue will tend to go dormant or grow slowly over the winter months.
By our calculations, you should look at sowing Grovemount Blue about 90 days before your last frost date.
Ensure that temperatures are mild and all chance of frost has passed before planting out, as Grovemount Blue is a hardy plant.