Soil prep, temps important for seed germination

Many people contacted me about whether they could plant seeds or put transplants into the ground because of this unusually cold weather. My answer was the same to them as it is here. It depends.

Soil preparation and soil temperature are very important for successful seed germination, preventing plant diseases and encouraging root growth of transplants. Soil preparation and increased soil temperature are interrelated, which we tend to forget.

“Fluffing up” the soil with amendments such as compost allows warm air to enter the soil. These soils also cool off rapidly at night but can be planted earlier than soils not “fluffed up.”Amended soils warm up quickly, particularly if they are in full sun. This means amendments such as compost are rototilled into the soil or double dug into these future growth areas.

Preparation of the soil before planting, the location of the garden spot in relation to the sun and the type of seed or transplant affects what and how soon we can plant after cold temperatures pass.

Warm-season plants come from the tropics and include tomatoes, peppers, potatoes, squash, melons and annual flowers like impatiens, marigolds, petunias, geraniums, salvia, celosia and zinnias. These require warm soil temperatures of 60 to 70 degrees at the time of planting.

Cool-season plants such as peas, beans, spinach, radishes, beets, pansies, snapdragons, sweet alyssum, California poppy, godetia, larkspur, violas and bachelor’s buttons can handle cooler air temperatures and soils 40 to 50 degress. So they can be planted earlier than warm-season types.

Within the cool- and warm-season groups, different plants — even varieties within these plant groups — vary by quite a bit. If you aren’t sure, check seed packets for the best soil temperature for germination or online sources for the best root growth of transplants. Use a soil thermometer, with its tip pushed into the ground about 1 inch deep to measure soil temperatures and to gauge when to plant seed and transplants.

Q: My neighbor is concerned about the effect of the snow on her apricot tree. She said her tree was in full bloom when it snowed. Any advice?

A: There is nothing that can be done to lower the freezing temperature. The most susceptible parts of fruit trees to freezing temperatures are the flowers when they are fully open. Generally, open flowers can tolerate temperatures to freezing and nothing below that when they are fully open.

Very young fruit and unopened flowers can handle temperatures slightly below freezing — only a couple of degrees lower — and then they are damaged or die. Commercially, sprinklers apply water to fruit if air temperatures dip slightly below freezing. Ice formation on the fruit acts as an insulator. But not for the flowers.

A couple of days after freezing temperatures have passed, squeeze the base of the flower and see if there was fruit set or not. If you can feel a small swelling at the base of the flower, then the flower and future fruit made it through the freeze. If it feels flat and there is no bump at the base of the flower, then it didn’t make it.

The second whammy was the cold weather preceding the freeze. Honeybees were not very active because of cold temperatures and overcast skies. If there are no honeybees visiting the flowers, then there will be no pollination and no fruit produced.

I put a short YouTube video together demonstrating how to squeeze the flowers to check if there is fruit or not. It’s available on my Xtremehorticulture YouTube channel. Otherwise, just wait, and you will find out.

Q: Yesterday my neighbor was kind enough to share a jar of apricot jam she made from her 2017 crop of fruit. She mentioned, however, that her trees in 2018 produced hardly enough fruit to go through the jam-making process. Is it possible that our warmish winter was a factor? I believe my neighbor’s trees came with the house, so she doesn’t know if they are the low-chill variety.

A: The weather was too cold for early flowering apricots and peaches in 2018 and again this year. In 2018, it was so cold and overcast that honeybees didn’t come out to pollinate the flowers, but temperatures were above freezing, so the flowers didn’t freeze. The result was poor fruit set in many early apricots because of poor pollination.

This year, it was also cold when early flowering fruit trees began blooming. These low temperatures, again, limited honeybee activity and resulted in poor pollination. On top of that, freezing temperatures occurred at least three times in February.

Open flowers and their potential for fruit production do not survive even the slightest freeze. If you had an apricot tree that was flowering during freezing temperatures, there is a strong chance it won’t produce much fruit this year.

The chilling requirement for apricot to produce fruit was met in both 2018 and this year. A lack of winter low temperature was not the problem. This year, poor fruit production will be a combination of low honeybee activity and freezing temperatures.

Q: My Fuji apple tree is 6 years old and has never had any flowers. Is it still maturing, or should I get rid of it?

A: Most of what you’re talking about depends on whether your apple tree was grafted or not and which type of Fuji apple tree you have. If you bought a tree grafted onto a dwarfing rootstock, you should see spur and flower development by the third to fifth year after planting. If it is not grafted but growing on its own roots, then it could take six or more years before it starts flowering.

Try reducing the amount of fertilizer applied to this tree by half. If the tree is growing well, then don’t fertilize it again. A young apple tree like yours should grow about 18 inches a year. If the average new growth is more than this, reduce or eliminate the fertilizer applied next spring by at least half.

Fruit trees that were planted in soil amended with a good quality compost might not need a fertilizer application for two years after planting. It depends on the amount of new growth each year. The high nitrogen content of fertilizers and some types of rich compost might push new growth excessively at the expense of making flowers.

When winter pruning apple trees, prune back last year’s growth to no more than 18 inches. Pruning back excessively long growth encourages fruit production closer to the trunk.

Q: Thanks for your article about mimosa trees and their short lifespan. Ours appears to have a disease problem and falls within that 15- to 20-year age span you mentioned. Can I plant a new mimosa tree in the same spot if mine was diseased and removed?

A: I double checked recommendations from plant pathologists before I got back to you just to make sure. You should not plant in the same hole or in the same vicinity of a previously diseased mimosa tree.

The disease organism can survive in the soil and enter a susceptible new tree if planted in that area. Trees resistant to this disease include redbud, oak such as heritage live oak or holly oak, ornamental pear, honey locust and pine trees.

Bob Morris is a horticulture expert and professor emeritus of the University of Nevada, Las Vegas. Visit his blog at Send questions to

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