Etymology of orchard
Solution 1:
No, you are almost certainly mistaken about any overt borrowing from German Obstgarten to produce English orchard.
You are struggling too hard to look for an added -r-, when in fact, it was already present in Latin (h)ort-(us) right from the get-go. There were also cognate Gothic words starting with aurt-.
However, there is nothing resembling the German word Obstgarten.
Regarding orchard’s etymology, the OED states the following:
Etymology
orig. OE. ort-ʒeard, parallel to Gothic aurti-gards garden, the first element of which is considered to be Latin hortus (in late and medieval Latin ortus, Italian orto) garden. Cf. Gothic aurtja gardener, and OHG. orzôn ( :– *ortôjan) to cultivate.
Already in 9th c., OE. ortʒeard passed into orcʒeard, orceard, whence ME. orchard; also, with recognition of the second element orch-yard, ort-yard, or, with later conformation to Latin hortus, hort-yard.
The word has had many, many, many, many, many — did I mention many? — spellings in its history since King Ælfred the Great first wrote about it in 897 ᴀᴅ.
The OED lists 44 (yes: forty-four!) different historical spellings of the word, divvying these many forms up into four main sets, denoting each set with a Greek letter and with numbers indicating the nth century (and “1” means from before 1000):
α.
1 ortʒeard, ordceard,
4 ortyerd,
6 ortyerde, ortȝard, ortiard, (ortesyerde),
6–7 ortyard,
7 ort-yard.β.
1 orcʒeard, -ʒyrd,
1–2 orceard,
(1 orcird, ‑yrd, ‑erd),
3 orchærd, (horechard),
3–6 orcharde,
3– orchard;
(4 orichard,
4–6 orcherd(e,
5 Sc. orchart,
6 ortchard, north. orchert, ‑erit).γ.
4 orchiard, orcheȝerde, ‑ȝarde, ‑yerde,
4–6 orcheyarde,
5 orche-ȝerd, orcheyerd,
6 orchiarde, orchyarde, orcheyard,
6–7 ortchyard,
7–8 orchyard.δ.
6 horteyarde, hortyeard,
6–7 hort(e)yard,
7 hort-yard: see hortyard.
Not a single one of those 44 historical forms bears any real resemblance to German Obstgarten, except insofar as the second element shares a common ancestor in Primitive Germanic with the second element of Modern English orchard. That second element was gart in OHG and geard in Old English, a word that also gave rise to yard in English, and which is closely related to the current Northern English word garth from Old Norse garðr.
Given this evidence, I believe your notion that Obst- contributed to orchard is wholly unfounded. All historical records stand against that idea.
Solution 2:
It is more likely from two OE words: hort from the Latin hortus for garden and geard from the Old High German gart. Making it a garden in the garden.
Phonetically it is a small matter for the leading h to be dropped, and then the dental t interacts with the guttural g to move the dental formation to the current ch before spelling was normalized.