A handful of tomatoes with some strawberries in the background
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Grow Great Tomatoes in Seattle

Are you interested in growing flavorful, vibrant tomatoes at home? While the beauty, taste and nutritional qualities of home grown tomatoes far surpass those of store-bought, local gardeners are often challenged growing tomatoes by our cool spring temperatures. Because each tomato variety has a set number of days, “from transplant to first fruit,” planting delays can significantly shorten harvests… Some years tomatoes don’t ripen at all! To improve your changes of a bountiful harvest, the goal is to plant early, while applying some tricks to keep your tomatoes happy and healthy until the weather significantly warms. Here are some techniques to improve soil quality, create a tropical paradise for your tomatoes and extend your growing season. Try one or all, the benefits are cumulative. For those interested in growing tomatoes in containers, many of these tips can be modified with excellent results.

Pick a Sunny Spot

Whether you are planting your garden in the earth or using pots, select a location that gets the longest sun exposure for your tomatoes. Even better if they will receive some radiant heat from a nearby source, such as a wall. Tomatoes love heat!

Heat the Soil

This step can be as simple as placing dark tarps or plastic over your vegetable garden. Not only will it start warming the soil, it helps destroy weeds and dries the garden bed so it can be worked for spring planting. An additional option is to consider creating a raised bed, to further increases soil heat and drainage. These can be simply made.

Heat the Air

Warm air is critical to your tomatoes success, so why not take advantage of solar energy by creating a structure to capture that heat. To further increase heat gains, place water-filled gallons inside. Warmth absorbed during the day is released at night. When days are consistently warm, the covering should be vented. When the nights have warmed up remove the cover entirely.

  • For very small gardens, one could try “Wall O’ Waters”. Resembling a teepee, they moderate temperatures by surrounding each plant with chambers filled with water.
  • For small-to-medium sized gardens, simple cloches can be made using sections of 1-inch PVC pipe. Simply push both ends of each pipe into the ground to form a row of arches—the longer the pipe, the taller the space. Cover with 4 or 6 mil clear plastic sheeting, securing with clips from a home center or nursery.
  • Another option is to build a more permanent garden structure at a height allowing for ease of movement. This can be done economically using scrap lumber to create a frame then covered with plastic sheeting—or design an attractive garden feature, topping with clear corrugated plastic (polycarbonate or P.V.C.), and side panels wrapped with 4-to-6 mil plastic.

Ready, Set, Plant!

Once the soil and air have warmed up, you’re ready to think about working the soil and begin planting. Remove the tarp and enrich your soil by working in any remaining cover crops, then adding composted manures, and a layer of compost mixed in to 10-12” deep. Your goal is to “Feed the soil, not the plant.” Choosing organic materials instead of synthetic fertilizers, creates fertile, well-draining soils with balanced nutrients that are released slowly for plant’s optimum use.

Using compost is like magic. Any soil structure can be improved by adding compost—It improves drainage in hard clay soils, and allows sandy soils hold more nutrients. In fact, adding compost is considered the single most important thing you can do to increase the health of your soil. This organic matter supports an intricate network of healthy soil life. Besides providing initial nutrients for plants, it adds beneficial bacteria and organisms to the soil. It’s also a worm attractant, since worms eat compost, and they in turn aerate the soil and provide recycled nutrients for plants.

Where to get it? Compost can be made at home or purchased locally from Cedar Grove. Good, dry compost smells sweet and earthy, and is pleasant to work with. Recommended dosages vary depending on soil conditions, but a good rule of thumb is to apply a 1-2” layer over existing well-draining vegetable beds and 1” layer for slower-draining (clay) beds. If you are creating a new garden bed, double this amount.

To further enhance soil health, pavers or other materials can be applied along pathways to prevent foot-traffic from compacting planting beds. Compacted soil structure is very dense, so there is less room for air and water to transport nutrients to roots.

Once garden beds are prepared, applying a soil cover will provide multiple benefits throughout the season: Saving water normally lost from evaporation; reducing weeds and keeping the soil warm. One commercial option is “Planters Paper”. Resembling black construction paper, it is water permeable, discourages slugs and disintegrates slowly during the season—whatever remains at the end of the season can be composted. Make cross-slits in the cover to plant through, or skirt around plants after planting. Red plastic is another tomato mulching option popular with gardeners. Unless the plastic is perforated, a watering system such as soaker hoses must be installed under the plastic.

When selecting tomatoes, choose a combination of tomatoes that ripenYellow Bell Tomato early, mid and late-season, in different sizes and colors for the most variety and length of season. Be aware that “determinate” tomatoes will set fruit and ripen as one harvest and “indeterminate” types will continue to set fruit and ripen all season long. See “My Favorite Tomatoes” below for possible suggestions.

Before planting, add a natural calcium source (clean, crushed eggshells or bone meal) to the planting hole to reduce chances of blossom-end rot. This disorder, resembling a black circle spreading from the bottom of a tomato, often occurs when fluctuations in watering stress the plant’s ability to absorb calcium from the soil. No need to throw out the plant! Adding additional calcium and watering more regularly—perhaps using a timer—will help turn things around. When planting tomatoes in containers, add extra calcium and organic nutrients and pay close attention to watering.

Plant your tomato plants deep, so they’ll grow heartier roots. Stake plants and set up your watering system, such as a soaker hose, while they are still small.

Basket of Tomatoes

Master the Art of Growing Tomatoes With a Class

Learn everything you need to know to get started growing tomatoes in Seattle, as well as starting a thriving organic garden in general, by taking a class with Tilth Alliance! We offer online and in-person, hands-on classes in multiple locations. Browse our upcoming classes and sign up today!

Keep the Water Off

Despite the Northwest’s rainy reputation, our dry summers work to our advantage against diseases such as late blight (Phytophthora infestans) and Verticillium wilt that affect plants in the tomato family. Over-wintering as fungal spores on infected plant debris or garden soil, they kill plants by limiting water and nutrients. Recognizable when leaves wilt, they quickly progress from yellow to brown and black. To minimize risk:

  • Keep water from splashing from the soil to leaves by using soaker hoses and reapplying an overhead cover before late summer rains start. This limits spreading of spores.
  • Select disease resistant plants. Check labels for late blight and Verticillium wilt resistance.
  • Keep the garden clean. Remove any infected plants as soon as possible

Attract Bees

After the tomato plants are settled in and blossoms start to appear, it’s time to attract a variety of pollinating bees into the garden. Partially open the structures on warm sunny days, but close at dusk to retain heat. If blooms are not yet plentiful, invite the bees by placing some heavily-blooming flower pots inside. Mint and daisy family plants such as lavender and marigold are excellent bee attracting plants. You can also try your skills at hand pollination. Replicate greenhouse grower’s techniques at home, by using an inexpensive electric toothbrush with frayed bristles. Brushing each flower lightly will mimic the pollinating vibration (sonication) of bumble bees.


Congratulations, now is the season when you relish and savor the abundance of delicious tomatoes from your garden. Whether eating them warm on the vine or creating gorgeous centerpieces for your dining table, the results are priceless.

Extend Your Harvest

As the air starts to chill — often late September — you’re bound to have tomatoes that haven’t matured. You may decide to let some ripen in the garden. If so, apply techniques to hold in warmth, especially at night. Cooler temperatures can dull tomato flavors, and make their texture mealy as if they were store-bought.

Another alternative is to bring your unripe tomatoes inside. Even solid green tomatoes ripen wonderfully, adding beauty to your kitchen and extending your harvest for a month or two. Remove foliage, wash then let ripen in large bowls on the counter (one layer deep, stacked up the curves). Keep them away from heat and sunlight. While not necessary, if tomatoes aren’t ripening quickly enough, an apple placed nearby can aid ripening by the natural out-gassing of Ethylene.

Prepare for Winter

The final step after harvesting is to prepare your garden space for the winter. A little effort spent here will greatly improve soil health for next year.

  • Remove all pieces of tomato plants — including leaves — from your garden.
  • Add additional compost and agricultural lime (calcium) to slowly soak into soil all winter.
  • Adding a cover will reduce weeds and soil erosion. If you plant a cover crop, it also provides nutrients and organic matter when worked into the soil the following spring. Or cover your soil with an organic mulch like burlap or leaves for the winter.

Get Creative

Now that you know the importance of building healthy soil and capturing heat for tomatoes, you may discover all sorts of new ways to accomplish this and make your next harvest even better!