I want to grow edible nasturtiums and calendula in containers. Do I need to grow them myself from organic seeds (need a source), or can I buy nursery plants and just grow them without pesticides?
You can purchase either the plants or seeds from a reputable nursery (preferably one that does not use pesticides) to grow edible plants.
If it is true that nasturiums grow best in "infertile" soil as some sites say, what is "infertile" soil? I'm assuming it means "don't add compost" but does it mean start w/ just topsoil or actually go full on and plant in sand or rock?
It pretty much means that you can grow this plant basically anywhere that provides plenty of sunlight and in any soil type as long as it drains well. Nastutiums are not too picky about where they are grown.
nasturtiums do not like really GOOD soil. the worst soil in your yard, in full sun, and on the dry side, will ensure beautiful blooms.
They were lush and green and now many leaves are turning yellow and falling off.
This article can help pinpoint the possible issue: https://www.gardeningknowhow.com/plant-problems/environmental/plant-leaves-turn-yellow.htm
Will deadheading nasturtiums promote new flowers?
Yes, picking or deadheading the spent blooms frequently helps the nasturtium plant produce more.
Should my nasturtiums (Tropaeolum) be seeding by now? I planted them in the garden as seedlings this summer; they have grown quite extensive and all flowered. There are a few flowers remaining but no seeds, as they haven't fruited yet. What should I do next? Thanks.
Give them a little more time, seed production on nast's is slow. This link might be helpful: http://mrbrownthumb.blogspot.com/2007/08/when-i-collect-nasturtium-seeds.html
I recently planted some nasturtium seeds and as they came up something has been eating the leaves and leaving the stems. I do not see slug trails - what can it be?
It could still be slugs or snails. Setting out a pan of beer will determine it or not. It could also be rodents.
I have planted edible nasturtiums, pansies, and violas, and like to use the flowers for salads. My question is about picking them. Do I pick these flowers at the top of the stem or the bottom (i.e. will a new flower grow in place of the one I picked, or should I take the whole stem off)? One gardener told me to take the whole stem of violas. A different gardener told me he doesn't know the answer. Me, well, I barely know a tulip from a sequoia, so I thought I'd better ask someone who does. Thank you very much in advance!
I would imagine this would depend on the types of flowers, as removing blooms of some plants does encourage reblooming. For the most part, however, I think taking the entire stems would be suitable enough for you. There will be plenty more stems and flowers in their place.