Summer in Greenland starts around May or June, peak in July or August and ease of in September depending on how far up north in Greenland you are.
If you want to experience midsummer it is a good idea to visit Greenland in July and in the beginning of August.
It is also worth experiencing early summer in the end of May and in the month of June. The same applies to late summer in the end of August and beginning of September. By then most mosquitoes and other insects have disappeared from the fells; the weather is often warm; ships, airplanes and excursions will not be as heavily booked as in midsummer and in the end of this period the fells will start taking on lovely autumn colours of red, yellow and brown.
The Arctic summer is short and intense and this is something the flowers are aware of. They explode in a wealth of colours. The ice fells glitter snow white or blue on their trip through the fjords. The inviting landscape seems perfect for hiking treks, sailing and fishing.