Starting all of your plants from seed may be nice if you have a heated green house and can follow all of the steps to get good starter plants but for most of us there are at least some plants that take too long to get going in the spring. This is why starter plants are great for all gardeners.
Professional farms located in the south west or maybe locally to you can provide you with a pack of starter flowers or vegetables for a reasonable price. They also take care to use seed that has been protected from seed diseases and use soil that is less likely to have bugs and organisms like nematodes which can eat your starter plants as they try to grow.
When looking for good plants you should find stocky small plants that look green and healthy. Starter plants that are allowed to sit at the store may often yellow from lack of watering or they can grow stringy and high with no leaf growth towards the bottom of the plant. Stay away from any plant that does not look healthy.
The size of the container is not always how to choose a plant for transplanting.
If you are purchasing trees or bushes you always want to get the largest plant that has the largest root bucket but if you are purchasing flowers or vegetables that will double in size within 2 weeks in your garden then starting with a 8 pack vs a pint size container will save you a lot of money.
Always purchase your starter plants from a good dealer. Many companies will stand behind their plants and offer a refund but you may find that only a few dealers in your area are willing to refund smaller 8 pack vegetables once they have been transplanted. Ask about their return policy before you make your purchase.
Plastic planters are fine and from personal experience I like them much better then organic peet planters.
Peet planters always restrict the growth of the plant’s roots. Some starter plant companies will suggest taring the bottom off but if I can’t get 8packs in plastic I always remove all of the organic peet planter because you want your roots to establish themselves before the rest of the plant gets too big and fruit begins to grow.
If you see a good deal on starter plants early in the season your soil may not be warm enough to support their transplanting.
A good thing to do is simply force your fingers into the soil in your garden and see if it feels cold.
If you do find your soil is cold you can warm it by placing clear plastic tarp over your beds for a few days. This will raise the soil temperature for planting but you may need to place a small cold frame bed cover green house over your beds to maintain the warmth for the next couple weeks.
You can also place all of your plants in a single raised and covered bed and then transplant them later.
I like to grow my plants closer together at the beginning then as a bed of onions or lettuce is harvested move plants from my reserve bed to the empty one.