Heritage tomato orange varieties. Photo / Supplied
The past week has felt a change in the weather. A string of warmer nights was welcome, particularly by summer-growing vegetable plants.
One of the most cold-sensitive vegetables is the cucurbit family: zucchini, cucumber, pumpkin etc. These guys really don't like it when the temperature drops below 10C. Corn and beans are equally sensitive to the cold. Capsicum, chilli and tomato are a little hardier, but tend not to actively grow when the nights are below 7C. However, we are now - hopefully - at the cusp of warmer nights and today I am writing about growing tomatoes.
There are a number of varieties of tomatoes and it can be helpful to know how you want to use them when selecting which ones to grow. Cherry tomatoes in salads and eaten fresh, or large tomatoes sliced into sandwiches with cucumber and ham. How about medium-sized tomatoes cut into quarters and served with dinner, tomatoes sliced on crackers with cracked pepper and cheese - how do you like your tomatoes?
With many heritage varieties of tomatoes now readily available, they come in all sorts of colours - yellow, purple, black, orange, green, striped and of course red.
There are plenty of options to choose to grow and plenty of ways that you can grow tomato plants at home. Each person who has grown tomatoes a few times seems to develop their own style and method of growing that suits them and their property.
Whether you are new to growing tomatoes or a seasoned home tomato grower, now is the time to be getting your 2021-22 crop growing.
Mid-October and Labour Weekend are the traditional time for planting out tomatoes, as well as most other summer flowers and vegetables.
Tomatoes grow best in a full-sun position, but sheltered from the wind. They grow best at 21-24C and do not thrive at temperatures below 10C or above 27C, and do not tolerate frost.
Tomatoes tolerate a wide range of fertile and well-drained soils tending acid within a pH range of 5.5 to 7. Some lime may need to be applied to very acid soils when growing tomatoes.
The plants perform best if they are rotated with other vegetable crops to prevent a build-up of soil-borne pests and diseases. They should not be grown in the same patch of ground year after year. This can be a problem in small gardens and greenhouses. If pests and diseases are not a major problem and the soil is boosted with regular applications of compost and fertiliser, then rotation may not be necessary. Tomatoes are also grown successfully in containers, and this is another popular option.
Prepare the soil by working in Tui Tomato Mix or other such products. Mix in the soil at least 30cm deep because tomatoes develop a deep root system in this range and are gross feeders. Work in tomato fertiliser before planting; tomatoes need high levels of phosphate, but low levels of nitrogen. Dressings of fertiliser such as Tui Tomato Food during the growing season are most beneficial. The use of slow-releasing Manutec Tomato Tablets or Jobes Tomato Spikes I have found the most effective for the ongoing feeding of tomatoes, capsicums and cucumbers in pots and containers.
Sowing and planting
Tomato seeds planted now will produce a crop in February–March, whereas tomato plants planted out now can produce ripe fruit from late December depending on weather.
For a successional crop, you may like to sow some seeds now as well as plant out some seedlings. Seed is best sown in a seed-raising mix in clean seed trays. Fill trays to about 20mm below the top then firm and level carefully. Soak the tray and mix until it is thoroughly wet before the seed is sown, and stand for a while to allow excess water to drain.
Sow seeds evenly across the tray and cover with a 3-5mm layer of seed-raising mix.
The best temperature for germinating tomato seeds is 21C to 24C. Germination will occur at much lower temperatures, but it is slower. It is beneficial to cover seed trays with a piece of glass and paper during germination, and to turn the glass over daily so as to remove any condensation.
A well-prepared tray should require no further watering until after seedlings have emerged. High humidity at the time of their emergence helps the seedlings shed their seed coats. Seedlings should be pricked out when the seed leaves (cotyledons) are fully expanded. In temperatures of 21-24C, this can be 6-12 days after sowing. Before pricking them out, loosen them by sliding a small label/iceblock stick/narrow teaspoon or similar under the roots, lift the plants by one of their seed leaves – not the stem - to avoid damage.
Only vigorous, healthy seedlings should be pricked out into a good-quality potting mix such as Tui Tomato Mix. Discard remaining seedlings. Transplant into 5-6cm pots at the two or three-leaf stage and give the seedlings ample ventilation, space and light. They can stand short periods of low temperature as long as day temperatures don't fall below 7C, soil temperature is about 10C, and the risk of frost is over throughout most of Whanganui, except possibly in upper Aramoho.
If necessary, cover with cloches or plastic over a frame or stake supports in the early stages to provide shelter.
Routine care
All tomato types should be watered and mulched thoroughly once the soil is warm. Once established, plants in containers need more-frequent watering and supplementary tomato fertiliser to complement the loss of leached-out nutrients. Be careful not to overwater or overfeed because this may reduce flavour. Also, avoid watering the foliage because this may lead to fungus infection. Apply water directly to the soil over the root area or use a watering can, soaker hose, micro-irrigation drippers or similar.
In mid-to-late summer, some like to remove the growing tip (terminal shoot) to three leaves above a fruit truss to discourage further height and encourage the remaining fruit to ripen. Laterals should be removed about once a week, beginning about three weeks after planting. They readily bend and break off from a healthy plant. Carry out this task when the plants are dry because there is less risk of disease infection. The same applies to unwanted foliage. As leaves grow older they shade one another and the fruit. Removing some improves air circulation and further reduces the risk of disease and allows more sunlight to ripen the fruit. Grafted tomatoes can be grown without the need to have any laterals removed because the more-vigorous root system will support the larger plant.
Pests and diseases
Some pests and diseases of tomatoes are damping off of seedlings, mites, whiteflies, tomato caterpillars, bronze wilt, nematodes, fruit flies, tomato psyllid and tomato blight. Tomatoes under cover are susceptible to whiteflies, mosaic virus, grey mould (botrytis), tomato leaf mould, magnesium deficiency, boron deficiency, stem rots, foot and root rots and blossom end rot. Many of these problems are rare and can be controlled readily if observed.
The two most common problems in Whanganui are blight and tomato (also potato) psyllid. Blight is a fungal problem and can be prevented and controlled with the use of Organic Certified Gro Safe Free Flo Copper or Yates Tomato Dust. The tomato/potato psyllid is readily controlled by the use of Yates Mavrik or Yates Success. Both these sprays are bee-friendly once dry.
Come and see us at the garden centre with a photo or sample of your plants if you encounter any of these problems, and we can advise on the best means of control.
• Gareth Carter is general manager of Springvale Garden Centre
Opinion: It's time to plant cold-sensitive summer vegetables.