by Phyllis Pugnetti, Yakima Master Gardener
It’s surprising how many gardeners plant their entire garden on a sunny day in mid-May and consider the job done! This is convenient, but won’t always get the best results. Some plants can be planted in early April, others want to wait until June or July, and a few prefer to be planted in August to harvest in winter or the following spring. Knowing your plant’s needs can improve plant vigor and yields, but patience is required.
Usually by the first part of April, the soil in a cold frame or low tunnel will have warmed to 45-50º for planting cool weather crops like peas, carrots, radishes, and lettuce. Once seeds sprout and have their first four true leaves, crack open the low tunnel just a little to prevent overheating, especially on bright sunny days. You only need to close the cold frame or low tunnel if temperatures are expected to dip below 45° for an extended time, or when there are strong winds.
If you don’t have a cold frame or a low tunnel, you can find simple instructions online, to build either type of cover for a garden bed. Setting up a cold frames in early to mid-March allows about a month for the soil to warm, before you set out seedlings. Soil temperature is more important than air temperature for seedlings. Cold frames are not a must, but will guarantee an earlier start in the garden.
Most crops grow better when their finicky preferences are met. For example, carrots and radishes come in short season and long season varieties. In our climate you can plant short season varieties in early spring when the soil is consistently above 45º and harvest before the temperature climbs above 80º. Growing through the heat of the summer causes them to become bitter, tough, woody, or insect damaged. You can plant again when the soil temperature drops below 85º usually around mid-August. Short season carrots and radishes won’t withstand repeated hard frost, so plan to harvest when the soil temperature drops to around 35º. Short season carrots include varieties like, Nantes, Danvers and Little Fingers. Most radish varieties are short season and include common varieties like, Cherry Bell, French Breakfast and Sparkler.
In Yakima, all long season carrots and radishes are planted around the middle of August and can be grown through the fall and winter. Plant a lot and you’ll still be harvesting in March. Long season radishes grow very large and include varieties like China Rose, Giant Cherry, Daikon, and Watermelon Radish. They develop a crunchy texture more like carrots and are very winter hardy. Long season carrot varieties include, Autumn King, Chantenay, Yellowstone, and Flakkee. Planting in mid-August allows these varieties grow to about 80% of their full size before consistently cold weather arrives. Under a thick layer of mulch, they will continue to grow slowly throughout the winter and early spring. Never cover the leafy tops with mulch. A planting under the eaves of a roof or in a low tunnel will keep excessive rain and snow off the roots preventing rot. The cold winter weather causes carrots and radishes to convert starches to sugar making them much sweeter than spring varieties. Winter radishes can grow to the size of tennis balls while winter carrots can grow up to a foot long, often reaching sizes of one to two pounds.
Leafy plants like, lettuce, chard, arugula, mustards, and watercress can be direct seeded the first two weeks of April. Whether or not they are under cover, they will sprout whenever the temperatures are right for them. Planting in a cold frame or low tunnel means that they’ll sprout earlier and be ready to harvest before your warm weather plants need the garden space.
Other plants like corn, melons, squash, and cucumbers need the air and soil to be 80-85º, which require later planting dates, around late June. These plants do well by sowing seed directly into the garden bed. Yet due to our short growing season, they can get off to an earlier start by sowing seed indoors 3-4 weeks before transplanting into a warm garden bed. The exception is corn—the drama queen! She demands soil to be at least 80º and doesn’t like to be transplanted, oftentimes showing her great displeasure by refusing to set ears. Placing plastic sheeting over the corn bed for a couple weeks will warm the soil above 80º for an earlier plant date. Starting seed early is important for all heat loving plants, otherwise they may not have enough warm days to fully ripen. This is especially true of varieties that take more than 100 days to reach maturity.
The very last crops to go into the garden are garlic, and perennial onions—also called potato onions. These are planted in October. Allow them to grow until the first hard frost then add 3-4 inches of mulch to protect the roots through freeze-thaw cycles. In the spring these plants will be among the first to grace our gardens. Plan for a July harvest.
Planting early doesn’t always assure success. If the soil and nighttime temperatures are too cold it can permanently stunt or kill baby plants. Careful planning of planting dates will contribute to plant vigor, high yields, and the overall success of your garden. So be patient!