General Planting Info
When you're ready to plant, you'll want to amend the soil with compost, fertilizer, or both. Water the seedlings lightly about 15 minutes before removing them from their trays/containers. If the roots have grown aggressively, gently loosen them with your fingers. After planting you seedlings in the ground or raised bed, water them again. Not necessary but helpful: to prevent weeds and help retain moisture, apply a layer of mulch, like pine needles.
A Closer Look at Tomatoes
When to plant:
If your plants have their true leaves, but don't seem sturdy enough to plant yet, try moving them to a larger container to let them develop for another week or two. I try to do this anyway, just to get a stronger and more reliable plant.
Where to plant:
These guys like a lot of sun and rich soil. If you had tomatoes, peppers, eggplant, or potatoes in your garden last year, pick a different spot for them this year. Tomatoes are “heavy feeders,” which means they leech the soil of nutrients and all that good stuff. It also makes them more susceptible to disease. Most sources recommend that you not plant this group in the same spot for 2-3 years. Rotate in lettuce, spinach, carrots, chard, or onions instead.
Planting a marigold next to each tomato plant can help prevent nematodes, which can wreak havoc on your plants and fruit. I like to plant a row of marigolds on each side of my tomatoes, like a little fortress of flowers.
Once in the ground, frequent light watering of tomato plants can lead to shallow root growth. Instead, water your plants deeply once a week. Doing so can also prevent the fruit from splitting. Also, try avoid dirt/mud splashing onto the leaves when watering, this can lead to an unhealthy/diseased plant.
Don't forget to trellis or stake your plants! And don't wait to long to give them that support; once your plant is established, you can damage the roots by sticking a tomato cage around it.