Guest Contributor: Cassey Anderson, Horticulture Agent, Colorado State University Extension
Which Crops Prefer Which
March for many of us launches the beginning of “being able to actually DO something in the garden” season. But how do you know what to start at home or buy as a transplant versus what you can directly plant into the ground and still expect successful harvests?
Let’s dive into the primary categories.
Start Indoors: Crops That Need Transplants
This article won’t go into too much detail about what you need to start seeds inside. That is covered elsewhere in detail. However, there are quite a few plants that benefit from starting inside or purchasing as transplants. The reasoning for this is that they have a longer growing season for successful harvest. If you have a 100-day growing season and your crop takes 110 days to grow to maturity you likely won’t get very good results unless you start earlier inside or start with a small seedling.
Tomatoes
Tomatoes are probably the most infamous crop to start growing indoors or purchase as transplants. If you start seeds yourself aim to start seeds 6-8 weeks before the last frost date in your area. Transplants are ideal if they have 5-7 leaves and are a little thinner than a pencil.
Peppers
Peppers should be started 8-10 weeks before the last frost. They appreciate very warm soil (80F!) and can take their time to germinate; some may take up to three weeks. Peppers can be comfortably transplanted once the risk of frost has passed and the plant has 5-7 true leaves.
For both tomatoes and peppers, if you are purchasing transplants bigger is not necessarily better. Seek out smaller plants with good color. If there are already flowers (or even fruit!) you will want to remove those so the plant can focus energy on establishing roots in your landscape.
Broccoli
Broccoli can be started 4-6 weeks before your last frost date or purchased as a seedling with 4-6 true leaves. To ensure success plant 2-3 seeds in each container and thin down to one seedling once germination has occurred. Broccoli likes moist but not wet soil to grow well indoors. Avoid stressing the plant as stress can lead to bitter flavors which can persist beyond the period of stress. Sweet broccoli is much nicer than bitter broccoli!
Hardening Off Your Transplants
With any transplants you will want to harden your seedlings off prior to transplant and also to ensure you have prepared your garden for them before you bring them outside. To harden off you will bring them outside to a sheltered area for increasingly longer periods over a week or to leading up to your transplant day
Direct Seeding: Crops to Plant Straight in the Ground
Beans
Beans need warm soils to grow well but do not tolerate being transplanted. Ensure soil temperatures are at least 60F before transplanting and ensure you give them enough space to grow. Planting too tightly can lead to reduced yields.
Carrots
Carrots, and most root crops, are best suited to direct seeding because you don’t want to disturb the root which eventually becomes the vegetable we eat. Carrot seed can be planted in cool soils but ensure the soil stays moist as carrot seedlings cannot push through dry or crusty soil successfully. Unless you are planting with seed tape you will likely need to thin your carrots once they have germinated.
Peas
Peas are the early season gardener’s dream! They can be planted very early in the year or as soon as soil can be worked. To ensure best success you can pre-germinate pea seeds by soaking them in water or in a sealed container with a damp paper towel for around 24-48 hours prior to the intent to plant. Seeds can be planted deeply (1” or so). If this is the first time you have grown seeds in your garden you could benefit from amending the soil prior to planting with pea rhizobia to ensure good nitrogen fixation on the roots of the pea plant.
Flexible: Crops That Work Both Ways
Some plants are a little more flexible in their preferences and can be either direct-sown or purchased/grown as transplants.
Cucurbits
The vast majority of the time cucurbit crops such as cucumber, melon, pumpkin, and squash do best when planted outside, plant 2-3 seeds in each hole and thin down to one after germination. However there are times when seedlings get eaten as they germinate or other pest issues such as squash bug force you to delay your growing season a little. In this case you can start your seeds 1-2 weeks before the last frost date and plant 1-2 weeks after. Avoid planting very large seedlings, 1-3 true leaves will be sufficient.
Leafy Greens
Leafy greens are also flexible in their preferences for where to grow. Lettuce, kale, and spinach, can all tolerate growing indoors as seedlings to guarantee good germination, and can be transplanted when big enough to handle without breaking. If starting outside you may plant a little extra and need to thin your seedlings down (microgreen salads ensure no plants go to waste!).
Onions
Onions can be a very long-season plant but thankfully tolerate very cool soils. They can be direct sown up to 8 weeks before the last frost date or when the soil can first be worked. For better germination you might start your seed indoors and transplant when the seedlings are 2-4” long. You can also buy onions as starts (green young seedlings often sold in bundles) or as sets (miniature onion bulbs, often don’t size up as well as seeds or starts). When selecting your onions do familiarize yourself with your growing season – if you are growing in the summer when days are long you will want to seek out “long day” varieties. If you grow in the winter you want to find “short day” varieties of onions.
As always, reach out to your local Extension office for further information if you have any questions.
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