Tomatoes Q&A, 4/13/21

Tomato Veggie Happening, April 13, 2021

We were unable to respond to all of the questions during our April Zoom event. Therefore, we are sharing answers to questions addressed and not addressed during the Q&A portion of the Zoom event. You will find additional information on our Food Gardening Resources page.

1. How deeply should I plant my seedlings?

You should strip off all but the top few inches of  stem and leaves and plant the seedlings so that all of the stripped stem is buried, and the plant stands about 3 to 4 inches above the soil. New roots will sprout from the buried stem, making for a healthier and stronger plant.

2. I’m in east Santa Rosa, near Oakmont. What are the consequences of planting starts now?

Since warms days are predicted, especially on Sunday and Monday, there are probably no consequences. Watching your microclimate, you should avoid planting tomato starts when evening temperatures are in the 40s and below, and when we have strong winds. Ideally, you are looking for a soil temperature of 50 degrees and a night time temperature of around 60 degrees.

3. What are the best companion plants for pest control, how many per square ft.?

The efficacy of companion planting has come into question. In order to have the desired effect, very large quantities of the companion plants are needed—far more than are practical for the home gardener. It’s a good thing that tomato plants are susceptible to very few pests. Horn worms are the biggest pest problem and can easily be controlled by hand picking. Having said that, it is always desirable to include flowering plants that attract bees and other pollinators. Allowing some of your herbs to flower provides nectar and pollen for bees and beneficial insects.

4. What are the considerations for container growing, i.e. fabric grow pots, etc.

Many of the tomatoes on the market are really too big for a container. But if you choose your tomato plants wisely for size, containers are a great option. The soil in containers will warm more quickly and stay warmer than in-ground plants. This is generally a good thing, but containers will impact your water requirements. Containers will dry out more quickly than in-ground plants. Water moves differently in a pot than in the ground which is why we use potting soil instead of garden soil. Fabric pots, as you mention, are fine as long as they provide adequate space for your container tomato’s roots—generally 5 gallons. There are a few very small patio tomato varieties that do well in smaller containers.

5. I started tomatoes from seed about 6 weeks ago and they are just now barely getting their mature leaves. I started them in a sunny window. I am wondering what happened. Could it be too much water?

It may be water, but it is more likely temperature. The best practice is to start tomatoes and peppers on a heat mat. Don’t worry. Once the weather heats up, your plants will catch up.

6. Container size for one tomato plant?

A 5-gallon pot is about right. 

7. How much to water? Can you be specific like how many inches a week?

This is a hard question. There are so many variables—soil type, container, bed or in-ground planting, weather, wind, etc. You need to water consistently, best by drip irrigation, being careful not to get leaves wet. Keep your soil moist but not wet. Blossom end rot is a common result of inconsistent watering. Set your system to water a consistent amount and insert your finger into the soil to determine when additional water is needed. As a general rule, tomatoes need about one inch of water during a typical summer week in Sonoma County. You can find information and a worksheet on our website that factors in the characteristics of your drip system (e.g., GPH of emitters, spacing, etc.) to determine how long to run your drip system. Ideally, the weekly water need is divided into equal portions to be applied daily (or every other day if there are water restrictions).

8. When planting companion plants like marigolds, are they as effective planted at the same time with the tomatoes, or should you plant them before?

Companion planting has come into question. Research has shown that the number of companion plants needed to achieve the desired effect makes companion planting of limited value for home gardeners. Luckily, tomato plants have few pests. Also see answer to Question 3.

9. Where can I buy sungold starts?

Most places. They were at Harmony Farms and Prickett’s Nursery this past week. They will be available at the Harvest for the Hungry sale next weekend. Very common. Very popular and delicious. 

10. Will this webinar be recorded and available later?

Yes. The webinar video is posted on the Sonoma County Master Gardener YouTube site along with recordings of previous zoom events.

11. What role does soil temperature play and how can we influence it?

Tomatoes are warm-weather crops that thrive when the soil is at or above 50 degrees and when night air temperatures are in the 60’s. Lower temperatures and winds will cause your plants to stall, but they will catch up when the weather warms. Frost, obviously, will kill the seedlings. You can protect your plants in many ways and raise the temperature. Many people use clear plastic sheeting around the tomato cage early in the season, creating a mini greenhouse. If wind is a problem in your area, sheltering from the wind with a screen or other method is important.

12. I planted vetch and cow peas in raised beds. When do I cut down and do I turn in, or just drop on top of the beds.

You want to chop and drop your cover crop and spread a little compost over it to encourage decomposition. It’s best to harvest a legume cover crop just as it flowers. However, if you are just now harvesting your cover crop, it will not have enough time to decompose before planting your summer vegetables. You may want to consider adding the green matter to your compost pile and returning it to the garden when it is finished compost.

13. How tall should a plant be before you allow flowers?

You can allow a plant to flower once it is well established and healthy. Perhaps 1.5 feet tall.

14. So many fertilizers on the market. Susan said to use a well- balanced fertilizer at the time of planting. Can you give a type or brand you recommend?

Master Gardeners cannot recommend specific products, but you should look for something with NPK numbers in the single digits, and with the first number (Nitrogen) equal to or lower than the other numbers. We believe in using good quality compost for ongoing soil maintenance. This feeds the soil organisms which, in turn, feed your plants. Rather than looking for a particular compost manufacturer, look for one of three major “seals of quality” for soil products: 1) OMRI Listed–Organic Materials Review Institute, 2) US Composting Council Seal of Testing Assurance, or 3) CDFA organic registered—California Department of Food and Agriculture.

15. Can leaves remain whole (for mulch)? I don’t have a way to chop them.

Yes. If you are using the leaves to retain moisture, they can remain whole. If you want the leaves to decompose and add organic matter to the soil, you should chop them or crumble them once dry. Note that some whole leaves can become matted during our rainy season and restrict adequate moisture reaching the soil around your crops if you are not running a drip system under the leaf mulch. Therefore, it’s best to chop leaves for the fall and winter food garden. You can run a lawn mower over a leaf pile to reduce particle size.

16. Can I buy a smaller bale of rice straw somewhere (half bale)?

Yes. The Sebastopol Feed Store sells half bales. Or share a bale with a fellow food gardener.

17. Can you talk more about leaves of indeterminate tomatoes? When plants are mature, I find there are so many leaves that I worry that the plants don’t have adequate air flow. Do the tomato fruits themselves need some sun. If I prune leaves, how much/little? PS, In late summer, I put a shade overhead, especially as I’ve pruned some leaves.

Where the weather is hot, you need a good cover of leaves to protect your fruit from sun scald. You may trim excessive foliage and suckers, but you can also promote air flow by planting your tomatoes with generous spacing. If you fertilize, avoid high nitrogen fertilizers which will promote leaf growth. Also see answer to Question 34.

18. Can you keep your straw from one season to the next, or do I have to renew.

You can keep your straw from one season to the next.

19. Should you incorporate winter mulch material into the soil?

Yes or you can remove/replace it with spring planting. If you intend to incorporate the mulch into your soil, it is helpful to cover the mulch with a bit of compost to assist in the decay of the mulch material. Ideally, winter mulch or chopped-and-dropped cover crops would have been covered with compost at least 6 weeks before your spring planting so that it would have had time to decompose on top of the soil before planting warm-weather crops into it. Given the timing, it may be best to add green manure (cover crops) to your compost pile. Or, if you are considering what to do with winter mulch (e.g., undecomposed leaf litter, rice straw or the like), rake it aside to plant your tomatoes and return it to use it as mulch for the summer food garden.

20. I’m confused by the suggestion to leave roots in the soil. Are you talking about the smaller end roots or also the main roots. 

Yes, both kinds of roots. The roots will decompose over time, adding organic material to your soil. If you have limited space and need to plant immediately in the same area, there is no harm in pulling the big, woody roots. Master Gardeners promote the “no-till” philosophy because turning and disrupting the soil disturbs microbe activity, releases carbon into the atmosphere, and increases weeds.

21. Can you put oak leaves on the soil after tomato harvesting? Do you need to crush them up or layer on whole? Do you leave them indefinitely, or remove?

Yes. You can leave them whole, or you can crush them. It is helpful, if you wish for the leaves to decompose and add organic matter to your soil, for you to crush or crumble the leaves and cover them with a bit of compost to speed decomposition. If you are using the leaves solely as a mulch, it is ok to leave them whole. Also see the answer to Question 15.

22. Why rice straw? What’s different than using hay?

Rice straw has few seeds. Hay has many seeds which will promptly come up in your garden if you use it as mulch.

23. Can you use sawdust as mulch?

Yes. However, in an organic food garden, you should consider how the original wood material was treated.

24. What are your thoughts on using walls of water?

They are expensive. They work well. You can accomplish something similar by wrapping the tomato cage in clear plastic wrap creating a small greenhouse.

25. What is the best well-balanced fertilizer to add? Ratio?

A good well-balanced fertilizer for tomatoes will have NPK numbers in the single digits, and the first number (N for nitrogen) will be equal to or less than the other two numbers.

26. Your opinion on the red plastic sheets that are sold to take the place of mulch. They are also claimed to increase yield due to the reflected red light.

We tried the red plastic sheets at Harvest for the Hungry with no noticeable effect. They were difficult to deal with and inconvenient throughout the growing season. Plus, using plastic is not a sustainable practice.

27. Is it possible to order tomato plants in advance of the Harvest for the Hungry sale on the 24^th to have minimal contact with folks?

Yes. See the Harvest for the Hungry website for instructions for how to order ahead of the sale.

28. I was told that heirloom tomatoes grow best when planted in pairs. Is that true?

We have not heard this anywhere.

29. If my seedlings have dampened off, is there any treatment that will help them to recover?

You can treat seedlings with cool chamomile tea to combat the fungus responsible for damping off.

30. What causes purple leaves on young tomato seedlings?

Purple leaves are caused by a phosphorus deficiency. Plants grown in soil that has a high pH or soil that is cold are less able to absorb phosphorus efficiently, even if the phosphorus is present. You can treat a phosphorus deficiency with compost, aged manure, rock phosphate or bone or fish meal.

31. My soil is too alkaline. Is there a way to lower the pH at the time of planting?

You can add sulfur to soil that is too alkaline to lower the pH. For more information, read “Changing pH in Soil.”

32. Comment on adding calcium at planting time to avoid blossom end rot.

Blossom end rot is caused by calcium deficiency, but also by inconsistent watering. There is no harm in adding calcium at the time of planting, particularly if blossom end rot has been a problem in your garden previously. However, be aware that inconsistent watering is also a potential cause.

33. Can you plant tomatoes in the same bed year to year.

You can plant in the same bed, but doing so increases the chances that your tomatoes, particularly paste tomatoes, will be subject to disease. For that reason, it is best to rotate your nightshade plants (tomatoes, potatoes, eggplants, peppers) and not plant any nightshade plant in the same bed year after year. If you cannot rotate your crops, you can improve the health of your plants and prevent disease by planting with adequate space between them for air circulation. Additionally, do not plant the same varieties of tomatoes in the same spot year after year, and select varieties known to be less susceptible to disease.

34. Can you talk about pruning tomatoes? Should I trim sucker growth from the bottom? How about pinching out the intermediary branches?

There is a variety of opinion in the tomato world about pruning tomatoes. Brad Gates believes in both pruning and pinching out intermediary leaves in order to force the plant to focus on fruit production. Other professional growers do not and suggest, if you have sufficient room, letting them reach their full growth. Lower leaves should, however, be stripped from the plant so that no leaves touch the soil for disease prevention.

35. Is there a great alternate crop for rotation?

Anything that is not in the nightshade family is a good choice. Since tomatoes finish in late September or early October, plants suitable for a fall garden are appropriate (kale, broccoli rabe, collards or any fall leafy greens or root vegetables.)

It looks like 2021 is shaping up to be a drought year. Check out our Food Gardening with Less Water page to find out how to conserve water in the food garden. Also, read Growing Tomatoes with Less Water.

Thank you for attending our April tomato webinar. The Master Gardener Food Gardening Specialists conduct a Veggie Happenings Zoom event every second Tuesday of the month at 12:30 p.m. The events are free but require registration. A couple weeks prior to the event, you will find the registration link on the Sonoma County Master Gardeners home page. We hope that you will join us again.

Do you have gardening questions? Currently, due to COVID restrictions, we are not accepting walk-ins or specimen drop offs at our Information Desk at the UCCE Sonoma office. Please send an email with your inquiry to mgsonoma@ucanr.edu. Our Information Desk team is checking emails regularly and will respond to your questions as soon as possible. If you live outside of Sonoma County, you can Google your county or state Master Gardener organization.