Extension Spotlight: When should I plant warm season plants?

April 29, 2019 GMT

If you draw a line across the country from Northern California to New Jersey, the last expected spring frost date for states above that line falls around the last week of April to the first week of May. So tying Mother’s Day, that falls on the first Sunday of May, to an important gardening date helps us all remember when it is safe to plant our summer gardens.

In western Oregon, we often think the summer gardening season should start earlier than Mother’s Day, because we see bulbs and shrubs flowering as early as February or March. These early blooming plants have adapted to frosty weather and will survive the cold of spring. Just look at how well the daffodils are doing this year despite a foot of snow that has lingered into early March.

However, the plants many of us like to put in our summer vegetable gardens will not do well if planted in cool soils below 60 degrees. These plants include corn, tomatoes, squash, beans, pumpkins, peppers, okra, melons and carrots. Currently soil temperature is hovering around 55 degrees.

This year our late winter and early spring weather pattern has given us another gardening problem to deal with, heavy snow and persistent showers keeping soils saturated. If your vegetable garden is in the ground and not in a raised bed, the soil is probably still too wet to plant. With the weather forecast calling for rain during the remainder of April, it looks like we will have to wait for a dry week or two in May before planting.

Many of us rush to plant our summer crop vegetable gardens every spring. Unless you have a greenhouse or a cold frame to start your plants in, you typically won’t gain by starting your garden early. In fact, tests done by land grant universities all around the country have shown that warm season plants will yield earlier and grow better if the plants are placed outside in warm soil after the last frost day.

If you place warm season plants outside in cool soils too early the plants will just sit in the ground waiting for a warmer, more hospitable environment. While your garden plants are waiting for good growing conditions, insects, slugs and plant diseases can often harm your plants even if a killing frost does not come after mid-April.

So be patient and wait for Mother’s Day before you set out your warm season vegetables and flowering annuals. Now you know why the Oregon State University Master Gardeners have their annual plant sale in early May each year — we don’t want you to buy your warm season plants and set them out too early.

To help supply you with locally produced plants of varieties selected to do well in this area, the OSU Master Gardeners will be having their annual plant sale at the Douglas County Fairgrounds on Saturday, May 4, from 9 a.m. to 3 p.m. We will be joined by over 40 local vendors giving you an outstanding selection of anything you might need for your garden.