How to Sow and Space Vegetables - 5 Tips
March 31, 2013 at 4:37 PM
We visited with a friend this weekend who is an enthusiastic but relatively inexperienced gardener. She has a new raised bed garden and has been following the square foot gardening planting plan we created for her, but she has been having trouble understanding exactly how to space plant starts, which do tend to come in a bewildering assortment of sizes. Here, then, are five general tips on planting and spacing to help grow the healthiest possible plants.
1 - Choose your varieties carefully.
It’s easy to grab the wrong seed packet or six-pack of starts at a garden center, especially if you’re in a hurry. Taking a little extra time to make sure you have the appropriate plant will make a big difference, though. If you’re trying to grow vining peas or beans, then any seed packet marked “bush” is not going to be a fit. Those plants will only grow two to three feet tall, and do not require trellising. Be sure to look for words like “vining” or “pole” - or a specified height of five to seven feet - on the packet or plant tag if you mean to grow on a trellis or other tall vertical support. Seed packets typically contain a great deal of information including mature plant height, ideal spacing, date or temperature ranges for sowing, days to maturity from sowing, and any required plant supports. Plant tags in pots of starts contain similar information.
2 - Think about the final size of the plant.
It is really helpful to visualize the size of a mature plant to understand its spacing requirements. Take an onion, for example. In home gardens, onions typically grow to about three inches in diameter. The small pots of onion starts you buy at a garden center may contain dozens of small plants, all clumped together. Before you plunk the whole pot down in the ground, think about the actual size of a mature onion. Take the entire clump out of its pot and very gently squeeze the soil, carefully teasing the roots of the plants apart from one another until you have them all separated. Don’t pull the tops of plant starts, which are very delicate. Once they individual onions are separated, you can plant them four inches apart. In a square foot garden, that equals nine onions per square. We plant beets and turnips with the same spacing. Smaller-diameter carrots and radishes are planted 16 per square foot, or four rows of four with three inches between seeds in any direction.
3 - Be sure you’re planting to the correct depth.
With seedlings, this is pretty easy. Using the example of lettuce starts, once you have separated the multiple mixed lettuces in a six-pack into individual plants, just replant them at the same depth in your garden as they were in the pot.
Seeds can be trickier. We have seen many people poke very deep holes to plant tiny seeds like arugula, carrots or lettuce. Seeds planted too deep may never germinate. A good rule of thumb for any seed is to plant no deeper than about three or four times its diameter. A sunflower, bean or pea can therefore be planted about an inch deep. Tiny seeds shouldn’t be planted any deeper than 1/8” - 1/4”. And be sure to keep those seeds watered in dry weather, maintaining a moist soil surface as best you can until they germinate. This can take up to two weeks or so for carrots!
4 - Plant starts: more is not necessarily better.
If a planting plan or website instructions for plant spacing says, for example, to thin plants to one per 18”, you’ll need to pay attention to that. You may have bought a six-pack of kale starts, but look carefully at the stems coming out of the soil. Most likely, there are quite a few more than six in there. Nurseries do this to make the six-packs look full and lush. But if you only have space in your garden for four of those kale plants, putting in a whole bunch of them in that same space is not a good idea. Most likely, none of them will survive to maturity and produce food for you because they are crowded and competing for nutrients, light and physical space. Better to compost what you don’t need (or give them to a friend) and have four healthy plants.
We once showed up at a client’s garden for a maintenance visit to see that she had decided the garden bed looked a little empty, and had bought six-packs of watermelons (seven plants total) and cauliflower (13). Then, not knowing any better, she had taken the entire blocks of root-bound little plants and stuck them all in one spot in the ground. Given that a single cauliflower requires about 24” of space and a watermelon will trail out about 12 feet, this was clearly not going to work.
Another friend bought a container of Swiss chard starts, and because he had paid good money for them, decided to ignore the recommended 12” spacing on his planting plan and to plant all two dozen starts in two square feet. He was hoping for more harvest because he had more plants. Sounds good, right - better bang for the buck? But in fact, the chard grew leggy and diseased because of over-crowding, and never did produce a meal.
5 - Seeds: thinning is really important.
We have had countless conversations with beginning gardeners who are reluctant to thin plants they have lovingly germinated in their gardens. They often feel that it’s somehow unkind to do this - they just can’t stand the idea of killing a seedling. But if you don’t “kill” too-thickly seeded plants, most likely they will all die or will be much smaller in size and less healthy.
In seeding carrots, we drop two or three seeds into each hole, knowing that seeds do not have a 100% germination rate and this will give us a higher likelihood of full germination. It may seem fussy to make 16 shallow holes in a square foot and carefully drop a seed or two into each one - wouldn’t it be better to just scatter them? But carrot seed packets average over 700 seeds, and thinning a lot of carrots really can be a chore. However many you end up dropping in, once the seedlings are up, it is very important to thin them to their proper spacing, either by gently pulling out extras or by sniping them off.
Remember, your goal is to grow food, and if you pay attention to correct plant spacing, you are much more likely to reach that goal. One the one hand, plants spaced too closely will compete for nutrients and sunlight, become stressed, and eventually fail. On the other hand, too much space between plants is an invitation to weeds to take root. Proper plant spacing results in healthy plants that, as a bonus, provide a shade canopy that discourages weeds from growing.
-- Caroline Lewis