Most experienced gardeners will tell you what should be started indoors (or purchased) as transplants and what should be direct sown into the garden, but this can often be confusing for new gardeners. Add to the confusion the fact that some plants have a gray area when it comes to what is best, sometimes it depends on the time of year, and sometimes it depends on where you are as to whether what is possible. So if you forget to start your favorite tomato or begonia indoors in time to transplant, do you have options? Let’s explore!
Why start transplants, anyway?
This is a good question. Why do we take the time and energy to start seeds indoors, or the added expense of buying vegetable or annual transplants? There are a few good reasons:
- Germination temperatures. Many of the plants that we traditionally start as transplants require minimum soil temperatures of around 60F and have optimum germination between 70F and 80F. Waiting for soils to reach these temperatures, especially in cooler climates, can really shorten the growing season. Vegetable temperatures, via UNL Extension
- Extending the growing season. Related to germination temperatures, starting transplants for warm season crops before soil temperatures warm up and before the weather is suitable for planting can have a plant ready to go once those weather conditions are ideal. This can give you a head start of weeks or months over direct sowing.
- Ideal growing conditions. Seedlings for many vegetable and annual crops are quite tender and dainty when they first start out and any changes in temperature, water, or even sunlight can cause damage. This is even more important as spring weather is becoming a bit more unpredictable as the climate changes, where temperatures can drop suddenly and the weather can go from rainy to dry (or snowy) at the drop of a hat (he writes as the temps drop to the 30s and 40s from the 70s the previous week and some parts of the state are receiving 6+ inches of snow in late April).
What about direct seeding?
- Ease. Many gardeners, especially newbies, find it a lot easier and less intimidating to just hop out to the garden and plop seeds in the soil versus staring seeds indoors. Of course, buying transplants is equally as easy, but that does limit the variety you have available to plant.
- Cost effectiveness. Only needing a pack of seeds (or saved seeds) is typically much cheaper than buying transplants or buying the equipment than starting seeds indoors. This allows for much better cost effectiveness for gardeners.
- Some things don’t transplant well. Root crops, like radishes, carrots, and beets don’t transplant well because damaging that tiny little root in any way as you transplant can damage the actual harvestable portion of the crop and result in much lower produce quality (or even loss). Additionally, some plants don’t like to have their roots disturbed, even when they’re tiny little transplants. Cilantro and zinnias, for example, don’t do well with root disturbance so if you do want to transplant them you’ll need to start them in large enough containers so that you don’t have to repot them, and then plant them carefully as to not disturb the roots.
So sow, or not to sow? How do I know?
This is a good question. Oftentimes we can take a look at the seed packet and know, but sometimes we don’t have that packet or maybe we want to fudge a little with what we read on the packet. So what is possible, and what is “best practice”?
Using some of the information we discussed previously about soil temps and growing season, most of those warm season crops you plant that take a while to grow from seed, like tomatoes, peppers, and eggplants should be started as transplants, especially for folks in cooler climates (like most of the US). Same for those summer annuals (if you absolutely MUST grow annuals, I know some people love them and some loathe them). In warmer or topical areas, you may be able to direct sow these crops, but they may still do better as transplants.
Some of the warm season crops, like beans, corn, cucumbers, squash, and pumpkins can be started indoors and transplanted, but it isn’t necessarily needed. These crops typically grow much more quickly from seed and the seedlings are a bit hardier. We also typically grow some of these plants in much larger quantities, making them take up more space for indoor starting and resulting in a bit more work to transplant versus sow. Therefore, it is usually easier to direct sow these crops, but there could be situations (like overcoming weed pressure in the garden or if you have a really short growing season or low soil temps) where you might want to start them indoors.
What about cool season plants? Sometimes the answer to this one is – “it depends.” Lots of the leafy greens, like lettuce and spinach, and those aforementioned root crops can be direct sown into the garden well before the last frost date. If you have a soil thermometer, or a nearby weather station with soil temp probes, keeping an eye for when soil temps get into germination range can signal when to direct sow outdoors. The leafy greens can be started as transplants, but figure out the optimum soil temperature for gemination – for some, like spinach, it may be way cooler than your indoor temperatures can get (unless you keep your house around 45 degrees). For the Cole crops like broccoli, cauliflower, and cabbage, transplants should be started for spring planting, since they still require warmer (75ish degrees) temperatures for germination. However, if you’re sowing them for fall crops you can possibly direct sow them if other conditions, like water availability and low weed pressure, will support good growth in the garden.
There are several resources, like this graphic from Virginia Cooperative Extension, that can help you out. But keep in mind that certain situations may make other options possible. For example, this graphic is for spring planting, so some of the items, like the Cole crops, may have options for direct sowing for fall cropping depending on where you’re located and your local climate.
Source: Virginia Cooperative Extension Master Gardener Facebook
John I am so surprised about zinnia’s root sensitivity. I have always started my seeds, potted up and transplanted to garden. I often plant more than 1 seed together especially if the seed is old and tease the roots apart to pot up. Always thought they seemed fine with the process.
“Cilantro and zinnias, for example, don’t do well with root disturbance so if you do want to transplant them you’ll need to start them in large enough containers so that you don’t have to repot them, and then plant them carefully as to not disturb the roots.”
This makes sense, but how can we mitigate the risk that seedlings in large containers will suffer from water issues? I understand that such plants can have their roots rot due to surplus water, or they can dry out when water is pulled away from the soil surrounding their roots by the dry soil it touches.
Typically water is less of an issue with larger containers, as the large volume of soil holds a larger volume of water without saturation. The key is to make sure the containers don’t sit in water and to check on watering needs often to make sure they don’t dry out. For seedlings, using some sort of humidity hood will help slow drying out.