Planting & Seed Saving Notes

Tomatoes - The Complete Guide to Growing Tomatoes from Seed to Seed

Tomatoes - The Complete Guide to Growing Tomatoes from Seed to Seed

Tomatoes, Solanum lycopersicum

I don’t say this very often, but one good thing about a zombie apocalypse would be a reappreciation of the seasonality of tomatoes. The home grown tomato is iconic, and rightly so. The flavor difference between homegrown and commercially grown is dramatic, so much so that it may convince you to eat seasonally and avoid ‘fresh’ tomatoes in winter. Instead, plan to grow paste tomatoes for canning and drying. I always plant a large crop of Amish Paste and preserve the entire harvest.  

Growing Tomatoes from Seed

Tomatoes are a frost sensitive annual. In May and June, tomato transplants are readily available in plant nurseries and grocery stores (or at your favorite local seed company!). This is a great back-up and is certainly very convenient, but I encourage you to start your own tomatoes from seed. As well as opening up hundreds of tomato varieties, it’s a critical link in the seed saving process i.e. there’s no point in saving seeds if you don’t know what to do with them the following year.

Starting tomatoes from seed involves sowing the seeds eight to ten weeks (six weeks at the very least) before the last frost, and providing sufficient heat and light. The heat is to encourage germination and the light is to prevent the seedlings from becoming leggy by reaching for inadequate light. A sunny windowsill is rarely enough to promote stout, squat and strong plants, which means you need to provide supplemental light. That could be a shop light, a grow bulb in a desk lamp or a full spectrum grow light set-up. There is a set-up for all budgets, but you will need extra light for strong seedlings. Once you have lights you can use them for eggplants and peppers in the spring (alongside your tomatoes), growing microgreens in the winter and even starting fall starts indoors in July!    

Saving Tomato Seeds

The great thing about saving tomato seeds is that you can save seeds from many plants with very little concern about cross-pollination. The flower of a tomato is botanically perfect and self-fertile, meaning it has both male and female organs and can pollinate itself. The stigma in many varieties is also retracted, meaning a tomato flower can often be fully fertilized before it has even opened. So, most tomatoes only need an isolation distance of 10-20ft to prevent cross pollination between varieties. Even in a small garden it is quite possible to grow three or four different varieties without any additional steps to save pure seed. Make sure you consider this when planting your transplants out in May and June. The potato leaf varieties, such as the Brandywines, are an exception and need at least 50ft between varieties.   

One of the main challenges of tomatoes is the vast array of things that will kill them. This includes: Early blight; Fusarium crown and root rot; Fusarium wilt; Gray leaf spot; Gray mold; Late blight, Verticillium wilt, to name a few. I don’t have time to get into combating all these issues, but the simple act of seed saving can improve resistance in the seeds you save. My tactic has been to save seeds from the plants that survive all these diseases the longest. It’s a game of last man standing, or in my case, the five strongest plants at the end of the season. By saving from these plants I am selecting for natural disease resistance. Over the course of a number of years you are likely to see an improvement in performance (I’m into generation four for my Cherokee Purple and last year they already seemed stronger).

Harvesting the fruit is easy because the market maturity (when we like to eat it) and the botanical maturity (when the seeds are fully mature) are the same for tomatoes. If it’s good to eat then the seeds are also probably good. If you want to be extra vigilant then leave the tomato you want to save on the vine until it goes a little overripe. I use a permanent marker to write an ‘S’ on my seed saving tomatoes, this stops the dog from eating those ones. You’ll want to be prepared for processing your tomato seeds pretty soon after harvest so they don’t start rotting.

Tomato seeds are a great example of a seed that needs to be wet processed. The individual seeds have a slimy coating which is actually a placental layer to inhibit germination. It’s a natural barrier to stop the seeds germinating during a warm fall and then dying in a cold winter. The slimy layer keeps them dormant until it naturally breaks down the following spring. Stored seeds need to be clean and dry to cut down on possible disease vectors. The aim is to break down the slimy layer and this is best achieved through fermentation.

Steps for wet processing tomato seeds

  1. Cut the mature tomato in half.
  2. Scoop the insides into a glass jar.
  3. Depending on the liquid content of the tomato, you may need to add a small amount of water to cover the seeds.
  4. Cover the jar with something breathable. I like to use a coffee filter and a rubber band.
  5. Set to one side at room temperature.
  6. Fermentation will happen. The speed of the ferment will depend on the amount of added water, the temperature and the maturity of the tomato. White scum will form on top.
  7. After 48hrs strain the funky liquid into a jar and check to see if the seeds are still slimy. If they easily slip from your fingers add seeds back into the funky water and leave for another 24hrs. If they don’t slip, thoroughly rinse under a tap.
  8. Once they are non-slippy, lay out seeds to air dry. I use coffee filters for this too as they don’t stick to the seeds. Paper plates, screens etc. also work. Run a fan to speed drying and prevent mold.
  9. Store seeds in a sealed, well labeled container somewhere dark, cool and dry.
  10. Tomato seeds are well known for their longevity and if stored correctly can maintain good viability for up to ten years!

If the plant is 10 ft from a tomato of another variety then you are safe to save the seed, unless it is a potato leafed variety (i.e. Brandywine) which requires closer to 50 ft. Observing the position of the stigma in relation to the anthers can help assess the chances of cross pollination.
Good luck.

A note on Matt’s Wild Cherry tomato: this is a tomato that self seeds readily and grows aggressively. I hesitate to call it invasive, but at Sow True Seed we had one that climbed to the top of a nearby Dogwood tree and in my home garden I had this variety outcompete squash vines and climb corn stalks. To my mind, that makes this tomato a number one contender for the self-sustaining garden. I relocated my wild tomatoes to a rough patch of dirt on the edge of the garden, with the wild black raspberries. I think they’ll be quite happy and I’ll never have to worry about starting or saving those seeds.


Ready to grow some tomatoes? Check out our seed collection here!


Written by Chris Smith, author of The Whole Okra, and Executive Director of The Utopian Seed Project, follow him on Instagram at @blueandyellowmakes..