What a greenhouse actually buys you
A greenhouse doesn't make plants grow faster on its own — what it does is trap heat and cut wind, which extends the growing season on both ends. Seeds that would rot in cold, wet spring soil can start indoors under glass or plastic weeks earlier, and tender plants that would die at the first autumn frost keep going a few weeks longer. That's the whole mechanism: a more stable microclimate, not magic.
Where date palms don't fit
Worth saying plainly: date palms are not a greenhouse crop. They want full open sun, serious summer heat, and room for a root system and canopy that a backyard structure can't hold. Commercial groves are grown outdoors in hot, dry climates for exactly that reason — a greenhouse would do the opposite of what the tree needs. Where a greenhouse does earn its keep in date growing is much earlier in the process: nurseries use them to get young palm offshoots established before they're hardy enough to move outdoors.
What's actually worth growing under glass
Herbs, seedlings for the vegetable bed, and anything you want a head start on before the last frost — that's the realistic use case for a home greenhouse. Tomatoes and peppers started six weeks early under cover typically outproduce ones sown straight into ground once the weather warms.
Buying dried dates instead of trying to grow them
For most home growers, dates are simpler to buy than grow — the palms take years to fruit and need a climate few home gardens have. Kurma Supplier is a reasonable place to check current stock if that's the easier route, which for a backyard grower it usually is.