When did the Luftwaffe lose air-superiority over the Reich?

the Luftwaffe fell behind in producing sufficient numbers of competitive aircraft 1944 me 109 was past use by date and fw 190 failed against allied a/c 1944 small numbers of next generation nazi a/c weren't enough and pilot training fell short like every thing else needed in final year of war

It is difficult to pinpoint an exact date or even month when the Luftwaffe lost air superiority, because the Luftwaffe's defeat was a slow downhill spiral for about 18 months comprised of many smaller victories and defeats. There are 3 points along this timeline that could be considered the "loss" of Luftwaffe air superiority.

First, The allied bombing campaign against Nazi Germany was officially in full swing October 1943, and this is where the downhill slide begins. The Americans bombed during the day, and the British at night. The Luftwaffe had to begin contending with threats around the clock. Furthermore, the Luftwaffe was not yet concentrated at defending its home skies, but other fronts, primarily the Eastern Front.

Second, Mid 1944 is when the intensify was beginning to be felt in terms in 2 critically resources: fuel and experienced pilots. The Luftwaffe had plenty of aircraft and aircraft quality was debatably on par with Allied aircraft. However, if you don't have fuel and/or experienced pilots, having planes is worthless. Furthermore, mid-1944 was when allied escort fighters had arrived in sufficient numbers and with good tactics. This compounded the strain on Germany's war machine.

Third, in January of 1945, Operation Bodenplatte was the Luftwaffe lost any type of air superiority. It's fighter defenses were ill-spend on ground attack missions with ill-trained pilots, with much friendly fire. The losses in fuel and pilots could not be replaced. This was the final straw. From this point on, the Luftwaffe put up little resistance.

Part of the problem was the loss of experienced pilots and failure to impliment training programs to recirculate experienced pilots back as instructors.

Another aspect was the US switch to bombing oil refineries which began with a huge raid on the Leuna oil refinery in May 1944. Germany did not suffer so much a shortage of oil as a shortage of refineries, leading to a grave shortage of fuel in October 1944.

Jet aircraft were a partial solution because the Me-262 could operate on diesel fuel or even crude oil.

In reply to David West, yes a twin seat Me 262 night fighter was developed

The Luftwaffe did produce a crippling blow during the battle of the bulge knocking out Allied fighter bases in Western Europe however the German tank columns they were supporting became bogged down timewise trying to bypass Bastogne and ran out of fuel before they could capture Allied fuel dumps therefore lack of fuel was the greatest hindrance to German plans.

According to Dr. Richard R. Muller in his December 2003 article in Air and Space Power entitled Losing Air Superiority: A Case Study from World War II, he argues that the Germans had definitively lost air superiority over Europe in fall of 1944. Here he describes the final hope of the Luftewaffe to regain control of the skies, and the unlikely nature of such a proposition to succeed,

Another proposal that has attracted postwar attention was Galland’s suggestion to mass some 2,000–3,000 German fighters for a knockout blow. His goal was to commit this force against an American bomber formation in order to “shoot down an approximate total of 400–500 four-engined bombers against a loss of about 400 aircraft and about 100–150 pilots.”5 A victory on this scale would cause the Americans to cease daylight penetrations, restoring air superiority at a single stroke. In Galland’s view, Hitler scuttled this potentially decisive action by earmarking his carefully husbanded fighter reserve for support of the Ardennes counteroffensive in December 1944.

One has reasons to doubt the potential effectiveness of the “Great Blow.” While the operation was in the planning stages, considerable portions of the fighter reserve engaged American formations, but even under favorable conditions, the Germans did not down a significant number of American aircraft.6 The standards of German fighter-pilot training were so low by fall 1944 that the bulk of the 2,000+ pilots participating in the proposed operation would have been incapable of operating effectively. In particular, the task of assembling and controlling such a large quantity of aircraft in a single operation was probably beyond the Luftwaffe’s capability in late 1944.

It all started with North American P-51 Mustang which had sufficient range to escort US bombers in daytime raids:

General James Doolittle told the fighters in early 1944 to stop flying in formation with the bombers and instead attack the Luftwaffe wherever it could be found. The Mustang groups were sent in well before the bombers in a "fighter sweep" as a form of air supremacy action, intercepting German fighters while they were forming up. As a result, the Luftwaffe lost 17% of its fighter pilots in just over a week, and the Allies were able to establish air superiority. As Doolittle later noted, "Adolf Galland said that the day we took our fighters off the bombers and put them against the German fighters, that is, went from defensive to offensive, Germany lost the air war."

On 15 April 1944, VIII FC began Operation Jackpot, attacks on Luftwaffe fighter airfields. As the efficacy of these missions increased, the number of fighters at the German airbases fell to the point where they were no longer useful targets. On 21 May, targets were expanded to include railways ...

So, it appears that the "significant date" was April-May 1944.