Preparing the Soil
Days to weeks before transplanting
What is a soil amendment? Basically anything that you add to the dirt to give it new life, or really new "death" as soil is amended by adding organic matter from dead/decomposing/decomposed plants, simply detritus. Compost is a great soil amendment, but so are coffee grounds and leaf "mulch". Using a combination of compost incorporated into the top soil, and a good organic fertilizer will give your transplants a leg up in life.
Additionally, you may consider laying down black plastic for heat-loving plants like tomatoes, peppers, eggplants, etc. Black plastic is just what it sounds like, and can be found at most garden/hardware stores and online retailers that stock gardening supplies (I buy mine off amazon). Black plastic stretched over your beds will keep the soil warm, keep roots warm, suppress weed growth (NOTHING can grow through good black plastic that blocks the light), and keep things generally tidy. I lay down black plastic over the beds that will later house tomatoes, eggplants, peppers, squash, melons, corn several weeks before sowing to warm the soil. Then, I just cut holes in it where I want to plant, and dig in.
Buying the Transplants
Day of transplanting
I cannot advise enough that you plan your garden so that it isn't overcrowded or ill-timed. Once you have done that, transplants can be bought at the EHCG transplant sales (April 20 and May 18), the farmer's market, big box stores, online...many options available.
Beyond that, consider the specific plants you are buying, and what they need.
Transplants are of three general types:
1) Potted transplants: grown in pots of some sort. This is the kind of transplant we will sell at the EHCG transplant sales, and encompasses the most common transplants for vegetables, herbs, and fruits. Potted transplants usually have stems, leaves, and roots growing in at least a little bit of soil.
2) Bare-root transplants: consist of a green, living top with one or more leaves and a set of exposed roots (no soil). Strawberry plants and onion and leek “sets” are often sold this way.
3) Bulbs and bulb-like plant parts are not exactly transplants, but many are planted more like transplants than seeds. Garlic, potatoes, sweet potatoes, Jerusalem artichokes, rhubarb, asparagus,and many flowers are planted similarly. Unlike potted and bare-root transplants, bulbs store fairly well and don't quite need to be rushed into the ground.
Try to only buy as many as you really need and have space for. Lettuce transplants start out very small, but they will become large heads and provide lots and lots of food.
Day of transplanting
Most crops get transplanted into the ground at the same depth they were in the pot. So, dig a shallow (maybe 6") hole into the soil with a hand spade, shake the root mass and soil gently out of the pot, and transfer into the soil, aiming to keep the depth the same. If you are transplanting a heavy feeder, like squash, melons, or corn, it would be a good idea to add some organic fertilizer into that hole before transferring the plant into it.
A few crops get transplanted deeper than they were in the original pot. Transplant tomatoes very deeply in the soil, deep enough that only their first few bottom leaves are sticking out. We do this because tomatoes grow roots out the sides of their stems, and providing more underground stem means more underground root growth which means a happier, more stable tomato plant. Peppers and eggplants behave similarly, but usually we only transplant them a little (maybe an inch) deeper than they were in the pot.
Finally: WATER. Watering after sowing seeds or transplanting starts encourages root growth and keeps plants healthy. Do it thoroughly.
Be prepared to witness some transplant shock.
A simple metaphor: have you ever adopted a cat from a cat shelter, or moved with a cat or dog? Maybe not? Well, many pets do not adapt well to new conditions, and after being brought to a new home will hide, refuse to eat, exhibit hostile behavior, etc. Animals and plants alike are resistant to change in their living conditions, so be prepared for an unhappy response from recently-transplanted crops.
Transplant shock looks like droopy leaves, change in color, and generally is the outward manifestation of a process of sickness and healing that accompanies the change in soil conditions, light, wind, and access to water that is part and parcel of transplantation. Be patient, be calm, and be gentle. The plants will generally rebound before you know it.