This came up in my Political History of the USSR class this week and I had to look it up. The first German settlements in the Transcaspian region of the Russian Empire were founded in 1892. Some 50 families from the Volga established the villages of Krestov (near Sarakhs) and Saratov (near Ashgabat) at this time (Krieger, p. 14). In 1904 villagers from the Saratov settlement founded Kozelkov in the region of Bairam-Ali near Merv. Following this move, difficult economic and climatic conditions led to the dissolution of the original Transcaspian Saratov colony (Krieger, p. 85). The 1926 Soviet census counted 1,276 Germans in Turkmenistan of which 595 lived in the rural areas of Merv Okrug concentrated mostly in the villages of Kozelkov and Krestov and another 296 lived in the Turkmen capitol of Ashgabat (Krieger, p. 101). Much larger German populations lived in other areas of Central Asia including 4,291 in Kyrgyzstan, 4,646 in Uzbekistan and 51,102 in Kazakhstan. By 1939 the German population of Turkmenistan had grown to 3,346 versus 2,022 for Tajikistan, 10,049 for Uzbekistan, 11,741 for Kyrgyzstan and 92,571 for Kazakhstan (Krieger, table 1, p. 133). As can be seen from the census figures the German population in Turkmenistan remained quite small compared to the settlements in the northern regions of Central Asia.
Source: Viktor Krieger, Rein, Volga, Irtysh: Iz Istorii Nemtsev Tsentral'noi Azii (Almaty: Daik-Press, 2006).