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In the Garden: Focus on tomatoes after frost fear fades

SUNDAY, APRIL 14, 2013

Tomato plants are more productive when their bed is covered with red plastic mulch. (Susan Mulvihill)
Tomato plants are more productive when their bed is covered with red plastic mulch. (Susan Mulvihill)

If you were to take a poll on everyone’s favorite veggie to grow, tomatoes would win it hands down. Once you’ve tasted a sun-ripened, homegrown tomato, you’ll want to dedicate some space to the crop each year.

Tomatoes are a warm-season crop that should be planted in the garden, or in a large container, once all danger of frost is past. Here in the Inland Northwest, the average last frost date is around mid-May although you can really play it safe by waiting until the first of June to plant tomatoes and other heat-lovers like peppers, squash and eggplants.

I started my tomato plants from seed in mid-March to give the plants plenty of time to grow and because I enjoy growing unusual varieties that might be hard to find at local garden centers. This year, I’m growing San Marzano and Italian Pompeii paste tomatoes, Jet Star for slicing and my favorite cherry tomato, Sungold.

I start my plants in small pony packs but once the plant has a few true leaves, they’ll be transplanted into quart-size yogurt containers to give their roots plenty of room until they’re planted outdoors. Once a week, I give them some fish fertilizer diluted to half-strength to encourage strong growth.

Out in the garden, I prepare the tomato bed by adding organic materials like compost and shredded leaves. Then I place a soaker hose on the bed and cover the soil with a sheet of red plastic tomato mulch that has been anchored down with metal pins or bricks.

Research has shown that red mulch increases the amount of light reflected up into the plants, which in turn increases their productivity. I’ve used it for years and have gotten much better yields.

Next, I add a vertical support to the bed to give the plants something to grow on. I used to surround them with sturdy cages made from wire field fence but have since switched to an easier method. I grow them along either side of a 4-foot by 8-foot sheet of concrete-reinforcing wire that is supported with metal fence posts. It provides good support and I’ve found you can squeeze a few more plants into the bed. As the season progresses, I’ll weave some of the plants’ branches through the wire and occasionally loop some twine around the wire structure to give the plants added support.

A week before planting them outdoors, I begin the hardening-off process to prevent sunburn of the leaves and decrease shock. The first day, they’re moved outside to a shady spot for an hour, then back indoors. The second day, they go out for an hour longer, then back indoors, and so on over the course of a week.

On planting day, I cut an “X” into the plastic mulch every 18 inches. I carefully strip off the bottom two pairs of leaves off each plant and dig a large hole so I can plant them deeply to encourage additional root growth along the stem.

There is an exception to this method if you are growing grafted tomatoes, which I’ll write about in detail next week. Before planting them, study the lower part of the main stem to locate the place where it was grafted. It should look a little thicker there and you should see a horizontal or diagonal line.

That graft line must remain above the surface of the soil at all times; otherwise, the plant will sprout roots from the variety you’re planting and lose the benefits of the rootstock it was grafted onto.

After planting, give your seedlings a fertilizer that contains more potassium than nitrogen. Potassium is the middle number on the package and promotes flowering and fruit development.

Susan Mulvihill can be reached via email at her blog at for more gardening information, tips and events.

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