Beginning in 1888, when they first met while working on a house in Surrey, the pair worked together on creating homes of distinction such as this one in France: http://www.gardenvisit.com/gardens/les_bois_des_moutiers
After the end of the First World War Gertrude and Sir Edwin Lutyens, who was knighted in 1918, worked together on some of the cemeteries and memorials on the Western Front. According to Anne Powell, Gertrude planned “…to plant rose bushes so every grave would fall under the shadow sometime during the day. She extended the plan of an English country garden to the boundary planting, to reflect the hedgerows of home.” (p. 38).
Sir Edwin Lutyens gained fame when his work was reported in “Country Life” Magazine which began in 1897. He was one of three architects commissioned by the Commonwealth War Graves Commission, which at that time was called The Imperial War Graves Commission, to design memorials and cemeteries. Among his most famous memorials are The Cenotaph and Tower Hill Memorial in London and the Memorial to the Missing in Thiepval, Somme, France.
Sources: Wikipedia and “Gardens Behind the Lines, 1914 – 1918 Gardens Found and Made on the Western and Eastern Front”, by Anne Powell, published by Cecil Woolf, London in 2015