though it is only marginally perennial in my area (zone 6), I have been using Verbena canadensis as an annual here. They are typically sold at a nominal price....they are perfect for the cascading wall effect.. they bloom heavily but aren't a single blanket of blooms... a single plant can spread nicely within a single year.. blooming continually until the fall... and they don't need to be tended at all. They will root down where the stems touch the soil, but are very easily to pull up after the fall or in the spring. And they come in a few color varieties.

I have a dry stacked stone wall (think that's what it's called). Anyway, a lot of unusual things have volunteered in the pockets and crevices. Nepata, a daylily, and an iris. All three do well and look good. An episode of Martha Stewart showed her planting sedum in her wall. I tried that with no success. The hen and chicks was so shallow rooted it just kept falling. The dragons blood didnÂt survive the winter. A friend had the most spectacular wall planted in alyssum Âbasket of goldÂ. It literally stopped traffic when in bloom. The downside was when it was not in bloom.

Sounds like you are overwhelmed and confused. Don't be. All gardening is a matter of 'playing it by ear', so have fun and don't get bogged down with science! You'll learn as you go. That's half the fun. (1) Corn salad is a 'green', often called Lamb's Lettuce. See the link below. (2) These are fairly small pots, each of which will nicely fit a mature-sized parsley plant, or 3-4 smallish lettuce. Garden centres like to suck people in by planting out multiple-herb mini gardens, but you should regard them as something for gift-giving and for the short-term only. Nothing to stop you trying, however! For many people, plants in pots is the only way to go. Just don't expect miracles. (3) Design? Does it really matter? You can try to go all formal, with tall plants and the back and groundcovers in the front if you want; or you can do the cottage-garden thing and just jumble everything together willy-nilly; in a small garden bed like the one you're planning, it honestly won't matter a jot. It'll end up beautiful, no matter how you arrange it. But you're not going to end up with everything mathematically arranged like the French formal gardens, nicely manicured. Most herbs aren't like that - let's be brutally honest - most herbs are weeds! The important thing is to be able to reach whatever you want. That shouldn't be a problem for you in such a small area. I suggest you just put plants wherever you like them to be. If the plants aren't happy, you can always move them (well, most of them, anyway!). Herbs aren't quite as fussy as people where they go, in general. I agree wholeheartedly with FataMorgana: veges are herbs. Most of them have medicinal properties. But that's another topic. Here is a link that might be useful: corn salad

I'm no expert on companion planting, and there are whole volumes written on the subject. But in brief (and I don't pretend to be scientific about it!) there is a belief that certain plants do better when grown together. Sometimes one plant will keep harmful insects away from the other, sometimes one will bring useful insects to help pollinate the flowers of the other. Basil, for instance, attracts bees, which are needed to pollinate tomatoes, and so they make good companions. Sometimes you will have one plant some distance from another to act as a decoy. Garlic chives will attract aphids away from roses. Often you'll find that companion plants are members of the same family, and like the same conditions. Other times you'll find plants growing together that balance each other in their uses of nutrients - one may use a lot of nitrogen, the other might provide it. Some act in other ways to be good companions. For instance, Anise deters pests from Brassicas by camouflaging their odour and improves the vigour of plants grown nearby. It deters aphids, fleas, reduces cabbage worms.Coriander and anise seeds sown together will germinate more quickly. Borage accumulates silica and potassium, of great use when growing flowering and fruiting plants such as Broccoli, Brussels sprouts, Cabbage, Cauliflower, Cucumbers, Pumpkin, Tansy, Tomatoes, Rose, Squash, Strawberries. Chillies help plants which are affected by root rot and other Fusarium diseases. French marigold kills harmful nematodes. Horehound improves the fruiting of tomatoes. Yarrow is a good companion plant for most plants because it provides a lot of nutrients for them, especially those will need to produce their essential oils (the highly perfumed plants like lavender and basil, for instance). Yarrow is one of the so-called Physician Plants. Grown near a sick plant, it helps it to recover. Thyme is also a Physician Plant. So is marjoram/oregano. Some plants will help prevent grass and weeds from growing nearby. One such is Arrowroot, another is comfrey. Comfrey also is an excellent companion palnt because it keeps soil rich and moist, accumulates calcium, phosphorus, silica, nitrogen, magnesium, potassium, and iron, acts as a trap for slugs and because the rotting leaves make good fertiliser. I need to check this, but I think it's coriander which helps prevent fennel from seeding too much and becoming a weed, which it's otherwise likely to do. Fennel has the reputation for being the overall worst companion plant of all - it should be grown well away from other plants. It seems to inhibit the growth of many plants. Coriander (if such it be) is about the only plant which helps to control fennel. There are definitely some scientific reasons for all these things - some answers are already provided. I have heard that elder is a bad companion plant because the roots produce some substance or other which kills off competition plants - and I have found it true that nothing much...