How long have they been in the ground? If they were planted this spring, they probably dried out. Most new plantings need an inch of water a week. Watering them every day will kill them just as fast!! Bag worms could be the culprit, but you would probably see those on the plants. Like Ken said, attach photos.

T. Plicata 'Green Giants' grow taller in a manner where after each growth they have shot up a 4 inch or up to 3 feet tall main leader stem that is not very filled out. I do not suggest that stem should be cut off. Some people do it, but it's my opinion that the tree takes on a better growing form if that top slender main leader trunk is allowed to continue to develop. I have noticed that the tree along with its skinny top main leader will fill out much better if the tree is given some slow release food, during each spring and fall, high growth spurt. The non burning 3 or 6 month, slow release Osmokote fertilizer works well for my Green Giants. In addition, if yours are planted in clay soil, try to keep the soil only slightly moist. Otherwise the roots will struggle if the clay is allowed to remain too soggy. Such a conditon will drastically slow down the tree's growth and will even cause it to suffer more if once the soil gets dry and hard. On the other hand, if your soil where they are planted is quite sandy and drains rapidly, you will need to water your trees very often, and also often put down and mix into the soil lots of well processed, compost.

How wide is the area? I would lean more towards some spruce or pine trees... maybe a mixture of the two. But if you want privacy faster... the trees your talking about are Thuja Green Giants... they grow around 2-3' per year. I purchased some of these last spring that were maybe 1.5' tall in 1 gal containers from Great Garden Plants... by fall they were around 3'.

Good day all , I want to thank you all for your input , sorry if i didn't respond sooner was on mission and snowbanana i was able to find the Thuja growing in a hotel here in Dakar. i think what ken_adrian said is true they were not dying my bad . It is just that i brought also cuban royal palm and false ashoka tree and half of each of them died . To respond to Butterfly4u the type of soil is compost made from Casuarina equisetifolia and sheep manure. wisconsitom i will plant them in the ground once a move to my own house which is actually under construction .