Make sure the last frost date is past before you plant your tomatoes! Since there are many micro-climates in San Luis Obispo County, it is impossible to tell you what that date will be in 2017. The 2016 (average) last frost date was April 7th in Paso Robles and February 15th in San Luis Obispo. But every year is different, so be prepared! Check the 10-day weather projections. Cold evenings or a series of rainy days are not good for newly-planted tomatoes.
Choose a planting spot that receives at least 6-8 hours of sun each day. If you don’t have the most ideal spot, plant the tomatoes on the southwest-facing side of a building, where they can receive reflected heat from the wall and protection from the wind. Don’t plant where it is very windy, or in a low-lying area where the cold settles.
When preparing your tomato area, dig with a spade or rototill, loosening the soil 8″-12″ deep. Work plenty of good quality compost into the top 6″ of the bed, and add a cupful of compost to each planting hole or trench. Adding compost is the single most important step you can take in preparing your soil for planting tomatoes! Though compost is not high in nutrients, it greatly improves your soil with the organic matter it supplies.
Make sure you have balanced nutrients in addition to the compost. Tomatoes are heavy feeders and need nitrogen, phosphorus and potassium. It is also critical to have enough calcium in the soil to prevent blossom end rot. Agricultural grade gypsum is a good, inexpensive source of calcium. There are many organic and conventional fertilizers available that have the correct ratio of nutrients premixed, and will provide tomatoes with what they need for optimum growth. Follow the directions, mix the fertilizer thoroughly and don’t use more than recommended. Take care to place below the root zone so the plants can grow down into it and not be burned after they are transplanted.
Space your holes or trenches 24″-36″ apart, depending on the type of tomato plant. INDETERMINATES (tomatoes that grow all season, until frost) need more space than DETERMINATES (which grow and set fruit at one time and then stop growing).
Tomatoes like warm soil. You can help prevent transplant shock by covering the tomato bed a couple of weeks before you transplant with black plastic, which will absorb heat from the sun and warm the soil beneath. You can leave it on the bed after you transplant to help control weeds, or remove it.
An overcast or cloudy day is perfect for transplanting. If it is sunny and warm, planting in the late afternoon is best. It is beneficial to the plants to shade them for a few days with a light shade after transplanting.
Before transplant, trim off the bottom set of leaves; more if your plant is tall and leggy. Let the wounds from trimming dry before you put the plant in the ground.
Carefully remove seedlings from their pots so you don’t break the roots. (Water them lightly an hour before removing from the containers). If a plant is root-bound, gently work to loosen the ball and spread the roots out.
If you have dug holes, plant the tomato plant almost up to the remaining bottom leaves – it will grow roots along the stem and become a stronger plant. Don’t leave a long stem sticking out of the ground.
Planting horizontally in trenches helps the plant grow and produce faster, because the soil is warmer near the surface and tomatoes love the warmth! Dig a shallow trench and place the lower part of the stem horizontally in the trench. The top of the plant with leaves remains above ground (don’t force it upward; it will grow vertically towards the light).
Right after planting, water each plant well, watering slowly around the base of the plant. Water every day for the first week to 10 days. Give each plant a quart of water daily (in the morning), more if the weather is very warm. After the first two weeks, water an amount approximately equal to 1 to 3 inches of rain over 10 days, or even 2 weeks. The extra stress on the plant pushes it to produce fruit. When tomatoes emerge and are about the size of a quarter, water them 1 to 3 inches a week. It’s important to keep your watering pattern consistent once fruit is set. Keep watering patterns consistent to prevent cracking, blossom end rot and poor production. This will help to produce healthy tomatoes.
As the plant matures, water deeply to encourage the plant to grow more roots and seek water. A fully grown plant requires water consistently 2-3 times a week during the main growing season; about 1 inch of water a week; more if it is extremely hot. Watering tomatoes slowly and deeply prevents tomato problems. One of the best ways to water slowly and deeply is to use drip hoses or tape on a water timer. Do not water overhead or at night – it increases susceptibility to tomato fungus. Don’t Mulch tomato plants until they are well established, about 3-4 weeks.
If it is cold, consider using “Walls O’ Water” around the plants to help them stay warm. Tomato cages can also be wrapped inexpensively with clear plastic or bubble wrap. If you wrap the plants, cover the tops only at night and remove in the morning. Tomatoes can quickly develop diseases in a closed, humid environment.
Install tomato cages or stakes soon after transplanting to prevent damage to the root system.
Pest control: Cutworms can be a problem and can be excluded by placing a cardboard collar or sticks around the tomato stems at the soil line to keep the pests away from the plants. Check for aphids on the undersides of the leaves and treat accordingly. Tomato horn worms are hard to see until they have devoured a large portion of your plant(s)! You can pick them off, which is the easiest control.