Fill the pot to an inch or two of the rim.
Caring for Vegetables in Pots
Filling and Planting Your Pot
Once you have the right plant, pot, and potting mix for your situation, it is time to put them all together.
Before filling your pot, cover the drainage hole at the bottom with a piece of broken pottery, a coffee filter, or a square piece of screening or landscape fabric. This will keep soil from spilling out of the hole but still let water drain; don't use anything that will stop drainage. Then fill the pot with potting mix to an inch or two from the rim of the pot. This should leave enough room to plant your transplants and then fill in around them, if needed, to be sure that the roots are properly covered. Dig deep holes for tomatoes and other items for which deep planting is recommended.
Don’t press down and pack the potting mix. You may want to tap the pot on the ground or rock it back and forth a couple of times to settle the soil into air pockets. Water gently. Allow the water to drain through the pot, wetting the potting mix as it drains through. Water a second and a third time to be sure the soil is thoroughly moist. Excess water should be draining from the bottom of the pot. Take a look at your transplants to be sure that their roots are not exposed or planted too deeply, unless it is a tomato, which takes to deeper planting.
Watering
Never delay watering after planting.
Your potted vegetables will need plenty of water. You will know it is time to water when the top half inch of potting mix is dry to the touch. You will also learn which plant dries out the fastest. When that one is dry, it is time to water all, rather than letting your plants become stressed. Once plant roots have filled their pots and the weather gets hot in summer, you can plan on watering on a daily basis. Remember that fluctuations in soil moisture can worsen blossom-end rot in tomatoes. It is better to have constant moisture than to alternate wet and dry conditions.
If you are growing vegetables in pots during the winter in an area where temperatures could freeze the soil, your plants may wilt because the moisture in the soil is unavailable to the roots. If you have a sunny south- or west-facing wall, that is a good place to put your pots and grow your vegetables. Masonry is particularly helpful in creating a microclimate, releasing the warmth of the sun to prevent cold damage at night. See "Keeping Pots Watered"
for more about watering.
Fertilizing Your Pots
If you are growing vegetables that produce fruit, such as tomatoes, peppers, and squash, avoid fertilizing with too much nitrogen. Nitrogen (the first number in a three-number fertilizer formula such as 10-10-10) encourages leafy growth at the expense of flowering. For example, you may have a beautiful tomato plant, but few fruit. However, if you are growing lettuce, basil, or another plant whose leaves are your goal, nitrogen will fuel production.
In either case, you need to fertilize regularly and moderately. Some potting mixes have a short-term supply of fertilizer in them, so read the label. If this is the case, don’t add additional fertilizer for the first 2 to 4 weeks, depending on how often you have to water.
The frequent watering required by container plants will wash away nutrients more rapidly than if the plants were grown in the ground. Using a timed-release granular fertilizer helps. Better yet, fertilize regularly with a plant food that you mix with water. Try Bonnie Herb and Vegetable Plant Food. This what we use to grow the transplants in our greenhouses; you can continue it at home with great results.