If you want to grow a tomato plant that makes a lot of great fruit, start with a plant that isn’t blooming yet, not even showing a sign of buds. Buds are a sure sign that the plant is getting root bound and is trying to make seed before it dies. The plant has switched from vegetative growth to blooming and won’t grow much after you plant it. If the buds are still very small, you can pinch them and it might switch back. If it is blooming, don’t buy it or plant it.
It can be hard to find plants that are not blooming in the markets. Gallon plants always have flowers, and fruits abound. Even 4-inch pots are often budding or blooming. Your best bet is to buy 4- or 6-paks, and check them carefully for buds. Don’t despise seed. I’ve seen many a volunteer out-produce starts.
Tomatoes need warm soil, good soil, and regular water. Don’t plant them before the soil warms up a bit. Trying to beat the last frost is a losing game, because the plants won’t grow until the soil is warm, and pests will eat them. A good sign that it is time to plant is sprouting of volunteer tomatoes or other warmth lovers where they were grown the year before.
Spend some time preparing the ground first. If your soil is poor and grows small weeds, cover it with about 6 inches of compost and enough pine needles or coarse bark to cover, or a foot of mixed leaves from the fall. If it grows big, leafy weeds, two inches of compost may be sufficient to smother most weeds seeds and small plants. Pull whatever comes through the mulch.
Plant your starts into the compost or leaves if they are thick enough. If not thick enough, pull the mulch aside and dig in the soil a bit, and then pull the compost and top mulch back around the roots. Do not plant it deeper than it was in the pot; that will just make it easier for pill bugs to eat the leaves. A plant that is not root bound doesn’t need to grow roots from its stem.
Last, but not at all least, surround the plant with rocks, to soak up heat during the day and release it at night. Night warmth is critical to growth. A few big flat rocks are good; even better is a solid 2 to 3-foot circle of cheap river rock, called gabion rock at Copeland. Covering a bed with them produces the best results, but removing them each year for mulching can be a chore.
All of the above goes for peppers, with emphasis on warmth at planting time and starting small. They are even more likely to be blooming in 4-inch pots; look for 6-paks.
Squash, melons, cucumbers, corn and beans are all better off bought as seed and planted when the soil is warm. They hate any sort of root disturbance; seeds will beat anything started in a pot. Melons and cukes benefit from warming rocks; squash, corn and beans don’t need them. If your seeds don’t grow, the soil was too cold; replant.