Onions are a favorite vegetable of many home gardeners. They are easy to grow and can be enjoyed much of the summer and then stored for use throughout the winter months. I still have onions that I am using from last year’s crop! Onions come in many types from the small green bunching to the larger red, white and yellow types. They all can be grown in about the same way. However there are a few things that some gardeners may not know about growing onions that could help them to produce larger and better-keeping onions.
First of all it important to know that most onions are day length or photoperiodic sensitive plants. This means that depending on the length of the day, they will either start producing their bulbs or mostly continue to grow more leaves instead. Since we live in a northern climate and we grow our onions during the summer, we want to grow long-day type onions. Short-day onions are mostly grown in very warm climates, like down in southern Texas and California, where they actually plant in the fall and allow the onions to grow during the cooler fall and winter months to be harvested in the spring. There are also day neutral types that can be planted just about anywhere and do not depend on the day length to produce a bulb.
The next consideration is how to plant your onions. Did you know that onions are actually a biennial plant? That means that onions need two growing seasons to complete their life cycle – go from seed to flowering and produce seed again. Onions grow their bulb their first year, which is used to allow the plant to overwinter (in warmer climates outside). Then the second season the onion plant starts to grow again and produce a flower stalk. Most people use onion sets to plant their onions, which are actually onion plants that had their first year of growth halted when they had only produced a small bulb. When you plant that young bulb or “set” you allow that plant to resume growth and hopefully produce a much larger bulb for you to harvest and eat. But, often weather conditions will encourage set-grown plants to bolt or produce a flower stalk because the plant “thinks” it is now growing in its second year, instead of concentrating its efforts on making a larger bulb. One little tip, it is usually better to look for smaller sized onion sets than the larger ones because the smaller ones are usually less likely to bolt.
Onion plants are an alternative way to plant onions. The big difference here is that those small plants are still in the beginnings of their first year of growth so all they want to do is produce a nice big bulb to get ready for the winter. So, often the onions you grow from plants will be considerably larger than the onions you will get when you plant from onion sets. The challenge for many gardeners though is finding the onion plants. Some garden centers and discount outlet centers have them in stock, and they are also available from some online or catalog companies but they may still be difficult to find. They will usually come bare-root and bundled up with a rubber band. You can also start them yourself if you have a sunny window sill, some plant grow lights or better yet a little greenhouse space. Onion seed is available from many sources but again take note of the type of onions you are growing to get either long-day or day-neutral cultivars if you by seed or the plants. That information should be provided in the cultivar description. Onions plants are rather slow to get started so start the seed about 8-10 weeks before you plan to transplant them to your garden.
Onion seed can also be sown directly into your garden but look for a short-season variety or else they may not mature by the end of the growing season. Some onions take up to 120 days to mature, so look for some that need more like 90 days to mature for direct sowing.
Which ever method of planting you choose, sets, plants or direct seed, start by making a row in your garden. It is best to have the soil cultivated or rototilled before planting to loosen it up and make it easier to work with. Make a furrow a couple inches deep using a hoe or other device. If you are planting from sets, space them about 4-6” apart in the bottom of the furrow with the pointed end pointing up. Cover the sets with soil and firm it with your hands. The top of the set can be about an inch below the soil line. If the furrow is deeper than that, it is OK just don’t bury the sets too deeply. You can fill in the furrow a bit after the onions start to grow but usually the onion bulb will stick out of the soil somewhat as it grows.
Onion plants can be planted in the same manner, you just have to be a little more careful with the more tender plants. If you purchased a bundle of bare-root plants, carefully separate them and place the roots in the furrow. Space them out like you would with the sets, about 4-6” apart. Firm the soil over the small bulb at the bottom of each plant. If you are using onion plants that you grew from seed, you may need to carefully pull the plants apart from each other. You will likely rip off a few roots but that will usually not be a problem. Space them out along the furrow, making sure that you have the leaves extending up above the soil surface as you gently firm the soil around the plants.
Direct seeding onions is quite easy too. Just try to thinly sprinkle the seed into the furrow. You will probably end up with plants that come up too close to each other but that is OK, you can pull the young onion plants and eat them as green onions. Or, you can thin the row by pulling out the extra plants so that the plants you have remaining are about 4” apart. You can have them growing more closely together but the onions might get a bit crowded as their bulbs increase in size in mid-summer. Just pull out the crowded onions as you need them for eating and let the rest to mature in the garden.
The last step is to water the furrow thoroughly. This is particularly important for the onion plants to get good soil to root contact and get the plants off to a good start. Water again during dry periods throughout the summer. Drip tape or tube and soaker hoses work great with onions and other vegetable crops. They conserve water and can reduce disease problems in onions and other vegetables. Other than that, they are one of the easiest vegetables to grow. Try to keep the weeds down as best you can then harvest them as you need them or wait until the tops flop over and dry up, usually in late summer to fall.
Garden Planting Tips
By David Graper, SDSU Extension Horticulture Specialist
Lots of gardeners are anxious to get out and do some planting. Now is a good time to get started with some of those cool season loving plants like peas, lettuce and radishes that we can grow from seed. It is also a time when it is usually warm enough to transplant cabbage, broccoli cauliflower and related plants that can tolerate cool temperatures and even some light frost. Soil temperatures have remained steady or dropped the last couple weeks which will delay seed germination and emergence so be careful with planting warmer season crops until the weather turns around and stays consistently warmer with night temperatures in the 40s or 50s.
Planting vegetable seeds is traditionally done in rows in the garden, usually spaced far enough apart to allow room for the rototiller to get down the rows without damaging the plants. But in many cases plants can grow much closer together, making more efficient use of garden space if you have a small garden plot. You will just have to do a lot more hand weeding instead of using a rototiller. On the other hand, if a space is filled with a vegetable plant, it is less likely to allow room for a weed to grow. Denser planting works especially well for low growing plants like lettuce, radishes, or carrots that grow well close to each other, do not get real bushy and are fairly easy to harvest. This close-spaced planting is also usually done in raised beds where you try to use every bit of that bed to produce food. You also make the bed narrow enough so that you can reach into the bed to tend or harvest the vegetables without actually stepping onto the soil in the bed. This is often referred to as square-foot gardening.
Most of the time people will make rows in their gardens before planting their vegetables. The simplest method is to use some twine and a couple stakes. Put one stake at each end of the row and pull the twine tight. Then use a hoe to make a furrow, following the twine between the two stakes. When you are done, move both stakes over the desired amount then make the next row. This method works well but can be rather time consuming. An alternative method is to make a row marker by bolting cultivating shovels or similar stiff piece of metal, to a 2×4 or larger piece of wood, spaced out at the row width you want. I made mine to work with my rototiller, allowing some extra room for plants on each side of the rototiller tines. Then add a handle and some braces and you are ready to make multiple rows at a time. The one I made makes four rows the first time you use it. Then I turn around and put the outside shovel in the last row and use it as a guide to make three new rows, next to the first ones. It works really well if the soil is freshly tilled and not hard or too rocky. The only real problem I have with mine is that it is too big and heavy. It is a real chore to pull it across the garden but then again, I just made four rows at one time, so I accomplish quite a bit each time. I take a break from making rows to plant the ones I just made before making more. Only make as many rows as you need at one time so that you can plant into a freshly made row that will have nice moist soil in it.
Follow the seed label for planting instructions for each of the different vegetables you are planting. Larger seed, like peas and corn can be covered with a garden rake about an inch deep after planting. Smaller seed should only be covered with about ¼ to ½” of soil so don’t overdo it. If you have really heavy soil, consider covering very fine or small seed with peat moss or potting soil to give it a better chance of germinating and getting established. It is often difficult to see how thickly you plant fine seed so try to carefully sprinkle it by “feeding” it between your fingers as you keep your hand moving over the row. Small seed may also be pelleted to make it easier to seed and more visible in the row.