Onions, Leeks
Plant your onions from sets (= small onions bought in the garden store) as early as possible, by early March if possible and no later than early May. The final size of the onions depends on the length of the growing season before the summer solstice, when the days start turning shorter. Prepare your onion and leek beds with plenty of composted manure. Direct-seed your leeks or set out six-week transplants in early May. The leeks have an opposite growing habit to the onions. They grow very slowly in the beginning, looking like little spindly strands of grass for several weeks. By early July their growth picks up, and by the end of August they are growing before your eyes. Leeks can be harvested starting in September. They are very winter-hardy and will survive most winters in the Puget Sound area. Just leave them in the ground and pick them as you need throughout the winter. A good overwintering variety is Durabel.
Broccoli, Cabbage and Other Coles
Set out transplants for a summer crop in April, for a fall crop by mid-August and for a spring crop by the end of September. These vegetables need lots of nitrogen to produce well. Mix in half a cup of organic fertilizer in the soil under each plant at transplanting, and give additional fertilizer once a month, either by side-dressing with organic fertilizer or using fish fertilizer. To avoid having the cabbage maggots eat the roots and stunt or kill the plants, surround each plant with a ring of sawdust (available at lumberyards) about 1 foot in diameter and 2 inches thick to prevent the flies from laying their eggs close to the plants. To avoid the club root disease, deep-water the plants only once a week so that the soil is not constantly wet.
Spinach
Plant early April and again in mid-August to avoid having mature spinach in the heat of the summer when it will bolt (= go into bloom) very fast and turn bitter. If you insist on growing spinach in the summer, try to provide partial shade by other plants and choose a variety which does not bolt so fast (e.g. Steadfast from Territorial Seed Company). A good spring, fall and winter variety is Tyee, which is also very productive and disease-resistant in the winter. Prepare the soil with plenty of fertilizer at planting and supply additional fertilizer every couple of weeks.
Carrots, Parsnips
The carrot rust fly is a major pest of carrots and parsnips. I recommend building a 2' x 4' x 1' frame out of 1" x 2" furring strips and stapling mosquito wire to it. Keep this cage over your carrot and parsnips planting all the time so that the rust flies cannot get in and lay their eggs in the soil. This is especially important in the fall. The rust fly maggots will otherwise tunnel into the carrots and parsnips and make them inedible. Do not add manure to your carrot and parsnip beds within 6 months of sowing the seeds, otherwise the roots will develop multiple "fingers". Most soils will grow fine crops without any additional fertilizer during the growing season. If your soil is very poor, use fish fertilizer once a month.
Potatoes
Plant your early potatoes by the end of April and your late potatoes by the middle of June. Do not use manure or lime on your potato patch within 6 months of planting to avoid the scab disease. Do not plant the seed potatoes too deep, no deeper than 4", or they may rot in the ground if the spring is very rainy. As the plants are 4" tall, hill up soil or compost almost all the way to the top of the plants. When they've grown another 4", do this once more. Putting newspapers covered with straw between the plants and rows after the second hilling will keep the soil moist, the hills intact and the weeds down for the whole growing season. Deep-water only once a week when the weather has turned dry (usually by July). You can start digging your early potatoes by early July. The tops of the late potatoes will start dying off by the end of August. Two weeks before harvest, remove all tops (dead and live ones) from your plot. This is to prevent the potato blight, which may be present in the tops, from spreading to the tubers. The two-week waiting period is to make sure that the disease has disappeared and to harden the skins of the tubers for winter storage. When you dig your potatoes, let them dry in the sun for a few hours, but do not wash off the soil or they won't keep. Store them in a moist, cool place (basement, crawlspace, root cellar; not in your fridge) and they will keep for up to 6 months.
Tomatoes, Peppers, Eggplants
Do not plant out until May, unless you have a very warm and protected location. Always provide protection for the transplants for the first few weeks of the growing season, no matter how nice the weather is at transplanting. Use a biodegradable black paper mulch on your tomato beds (available at Seattle Garden Center) to trap more heat and suppress weed growth. Tie the vines of the indeterminate tomatoes to 6' tall 2" x 2" poles and train one or two tops up the pole. Determinate (bush) varieties can be supported with regular tomato cages. Do not prune the determinate varieties (unless they are too dense) and avoid excessive pruning of the indeterminate ones to avoid sunscald on the fruit. Tomatoes ripen in the dark, so make sure that there are enough leaves providing protection for the ripening fruit.
Corn
Select only locally adapted varieties from local seed companies. Presoak the seeds overnight and plant when the daytime temperature in the in 70s and the soil temperature is at least 65 degrees. Prepare the soil with plenty of organic fertilizer or chicken manure. Always plant your corn in blocks of at least 4 x 4 plants to ensure proper pollination, never in a single row. The harvest period for a single planting is just a couple of weeks before the corn loses its sweetness, so stagger several plantings a couple of weeks apart or plant more than one variety at the same time to get a longer harvest. Cover the bed with a sheet of heavy-duty clear plastic which can be reused to keep the soil warm and moist, and remove it as soon as the seeds germinate, which should be within 4...8 days. Supply additional fertilizer every 2 ... 4 weeks. When the corn is blooming, shake the tops on a calm dry day to allow the pollen to fall down on the silks and pollinate the kernels. To determine when corn is ready to pick, uncover a few kernels on an ear that feels full and punch one with your finger. If the juice flowing from the kernel is milky white, the corn is ready. If it is clear, wait a little bit longer.
Beans
Wait until the soil temperature is close to 70 degrees. This may not happen until the middle of June. Soak the seeds for a few hours and cover the bed with a sheet of clear plastic after planting. Do not water the bed until the seeds have germinated, otherwise they may rot in the ground. If the seeds do not germinate within two weeks, wait for warm weather and replant. Pole beans are tastier and easier to pick than bush varieties, but take a little longer to begin producing and need a good trellis about six foot tall. Even though beans may grow a lot taller than 6', I advice against building a taller trellis because the beans will be difficult to reach. Cut the tops of the vines when they've reached the top of the trellis to prevent overcrowding. It is very important to keep picking the beans as they reach proper size, because if you let the seeds inside the pods develop fully, the plant will stop blooming and producing more beans. A simple trellis is best, because elaborate tepees and other nice-looking structures tend to get too densely covered by the vines and the beans get hard to spot. Pole beans planted by the middle of June should start producing by the end of August and keep producing through October, unless the fall is very cold.
Cucumbers, Squash
Cucumbers will not germinate if the soil temperature is below 70 degrees. I therefore recommend that you start your cucumbers indoors by the middle of April for transplanting by early June. Providing protection in the form of a cloche or individual mini-greenhouses will ensure good growth from the start. As with other heat-loving plants, harden off your cucumber plants for about a week before transplanting. Zucchini and winter squash will germinate in a bit cooler temperatures, but setting out transplants is recommended. They are all heavy feeders, so provide plenty of nitrogen-rich fertilizer throughout the growing season.
Garlic, Shallots
Plant the individual garlic cloves and whole shallot heads in early fall in moderately fertile soil for harvest the next summer. Provide additional fertilizer in the spring for maximum size. They should be ready for harvest in the middle of July.