(CBS) — There is a possibility of frost in the overnight forecast as the temperatures are expected to dip to 35 degrees in much of the Chicago area. That could spell trouble for gardeners who got a head start on this spring’s planting in the past couple of weeks.

If you’re planting trees or bushes or most perennials, you’re fine. But the Chicago Botanic Garden’s Director of Horticulture, Tim Johnson, has this advice if you’ve already planted vegetables such as tomatoes and peppers, or your basil, choleas, petunias, marigolds, begonias and other summer annuals — cover them.

If you have not yet planted them, Johnson is advising you to keep them inside and hold off for another two weeks, by which time he expects overnight temperatures to be in the 50s.

The Saturday forecast is 20 degrees below the seasonal norms.

Despite that, Johnson says, there is plenty of other work that can be done in the area’s gardens. He says this is actually ideal weather to divide and replant perennials.

Johnson says for trees, bushes and perennials there is one other potential barrier — ground that is over-saturated. He says that if you can make the mud into a ball, it’s too wet to plant. But if you can take the wet dirt between your fingers and it flakes away, that’s just right.

Johnson says, between the cold and the rain, gardening has been “quite an adventure” this spring.