|flowers starting to blossom with this 1.5 month-growing potato plant/by D2M|
It's good to know that container gardening is possible in Metro Manila. Without having to go to Tagaytay, you can find supplies within Quezon City. If you are into potted plants and growing vegetables in pots and containers (yes, it's doable!), check out these sites for info and product supplies like vegetable seeds, flower seeds, potting mixes, fertilisers, etc.
Cedarhills Garden Center Facebook page
This garden center is located at #57, Mo. Ignacia Ave, Diliman, Quezon City. Check page for product and workshop info, and container gardening tips. Realliving.com.ph gives a good write-up on Cedarhills Garden Center here. BusinessMirror.com.ph also has an info article here.
Manila Seedling Bank is a known source. Confirmation needs to be made though if the foundation is still in operation. But here is an info article about it.