If you want really healthy tomatoes you need to grow them in a bed, rather than in growbags or containers. This is true whether you want to grow sungold tomatoes, other yellow tomatoes or traditional, red varieties
Tomatoes are very hungry plants, they need lots of water and nutrients and your tomato bed needs to be prepared now,k ready for planting out your young tomato plants in May next year.
Tomato plants have really deep roots that spread about two feet in every direction, which is why grow bags and containers are never really satisfactory.
You need a good depth of fertile soil in your tomato bed. If necessary move some soil there, or dump a ton of manure on there. Dig in the manure and let it stand over the winter.
Add plenty of slow release fertiliser such as bone meal, or blood,fish and bone and dig it in. Dig in rotted leaf mould or compost, even bury old cardboard under the soil to help hold water for your tomato plants’ roots.
The tomato bed’s soil is going to be the best in your garden, so weeds will grow quickly. Cover the ground totally with landscaping paper, covered with mulch to stop the weeds growing.. You will make small holes for the tomato plants when they are ready to go in.
Cover the bed with black polythene for a week before you plant your tomato plants, this will warm the soil and help them to get away faster.
Plant your tomato plants 2-3 feet apart. This is why you need the landscape paper and mulch to keep down the weeds.
You will have to repeat the bed ptreparation next year, beause you should not grow tomatoes two years running in the same bed, but whatever crop you grow there will do well, with all that organic matter and fertiliser, so it will not be time wasted.