We often get questions at the help desk from local gardeners who have lost many or sometimes even all their newly planted vegetable seedlings to one malady or another. Whether you have grown them from seed and tended your precious seedlings for many weeks, or have purchased them as young plants, this can be a heart-breaking occurrence. Here are seven steps you can take to give your young plants the best chance to survive and thrive.
Be patient and wait until the soil is the optimum temperature.
This applies for both purchased plants and for home-started seedlings. Your plants may have grown large enough to go into the ground, but if the outdoor temperatures are not yet at the optimal range, don't be tempted to plant them yet! When planted in soil that is too cold, many summer vegetable plants will just not grow. They are also more susceptible to being damaged or killed by fungal diseases. How does one know if the soil is the right temperature? The best way is to use a soil thermometer. A good kitchen thermometer will also work, although you may want to have one that is designated for use only in the garden. If you don't have a thermometer, watch for daytime high temperatures to remain consistently above 60 degrees and nighttime temperatures above 50 degrees. For more information on this, you may want to review our previous blog posting published on February 20th entitled: “Indoor Seed Starting."
Cool-season vegetables such as peas, cabbage, lettuce, carrots, cauliflower, broccoli, beets, and Swiss chard will do best when average temperatures range from 55 - 75ºF. Warm-season vegetables prefer temperatures that range from 65 - 95ºF. Examples of these are eggplants, tomatoes, beans, squash, melons, and peppers. Best planting times will differ for many vegetable varieties. Check seed packets or the planting guide listed below for information on the best dates for planting in your area.
CCC Vegetable Planting Guide-Interior Regions
CCC Vegetable Planting Guide-Coastal Regions
Avoid letting plants become pot bound.
Move your plants into containers that give them more room for healthy root growth. Transplanting into 4-inch, quart, and even gallon sizes is often necessary. Use a good quality soilless potting mix and avoid planting mixes and garden soil. To check if your plant needs a larger pot, gently tap the sides of the container it is in and carefully slide it out (soil, roots, and all) to look at the root growth. Transplant into larger containers before the roots begin to circle the edge of the soil, create a mat of roots at the bottom of the container, or grow out of the drain holes. Pot bound, stressed plants will often have early flower and fruit development. This can stunt their growth and impact the plant's health as well as reducing future harvests.
Harden off young plants to prepare them for their life outdoors.
Sunscald is a common problem in young plants and seedlings that have suddenly received more sunlight than they were previously accustomed to getting. Sunscald causes areas on the leaf to dry out and die, turning thin and papery and a white or light tan color. Most seedlings will bounce back from a moderate amount of sunscald damage and continue to grow new, healthy leaves. When the damage is so extensive that all or nearly all the leaf surfaces or areas of the stem are affected, the plant may not be able to survive.
To avoid this problem, plants must be hardened off. This is a process used to acclimate young plants and seedlings to the conditions outdoors. For seedlings that have been grown in a greenhouse, indoors under lights, or other protected environment, this is a crucial step. The hardening off process will take about 10 days to two weeks. Here is an excellent article from Penn State Extension with step-by-step instructions on how to harden off plants.
https://extension.psu.edu/hardening-transplants
Keep your plants safe from hungry pests- snails, slugs, earwigs, and birds.
Even the most experienced gardeners will lose some of their young vegetable plants to one or more hungry garden pests. My first suggestion is to always have a few extra plants to replace those that may get eaten. My second is if you have had problems in the past with one or more pests consuming your vegetable seedlings, start taking steps to control them before you plant. Don't wait until the damage is already done. The methods of controlling many of the pests are similar and include keeping your garden free of plant debris and favored hiding places, trapping, barriers, and baits. Baits that are safe for children, pets, and wildlife are available to the homeowner, and are very effective. Because they can take several days to take effect, it is best to use them in conjunction with the other suggested control methods. The best time to start using these control methods is several days to one week before planting.
Birds can also be a serious pest in the vegetable garden- especially early in the season as many vegetable starts are a favorite food. While there are many products advertised to scare birds away and keep them from eating your plants, bird netting is the solution that I find to be most effective. Make sure that the netting is raised above the plants to keep birds from reaching through to eat, and securely staked to the ground so that they cannot get underneath. Check your netting regularly, keep netting stretched snugly over supports, and avoid any loose ends that can trap and kill birds, lizards, and other wildlife. As plants mature, they are less attractive to the birds, and netting can often be removed. See one of our earlier blogs for more information on protecting your plants from a variety of pests: https://ucanr.edu/blogs/CCMGBlog/index.cfm?tagname=birds
Space requirements for healthy vegetable plants
Before planting it is important to consider the mature size of the plants, and the space necessary for them to grow and flourish. Vegetable plants do not do well in overcrowded situations where they need to compete for nutrients, water, and sunlight. They will tend to be stunted and much less productive than those that have plenty of room. For information on space requirements for a variety of vegetable plants, click here: https://ucanr.edu/sites/MarinMG/files/343708.pdf.
Transplanting tips, suggestions
If transplanting from flats with several plants growing in them, be sure to take up some soil with each plant as you carefully remove each one from the flat. If transplanting single plants from individual containers, try to remove them from the container with the soil as intact as possible to avoid root damage. This will be much easier to do if the plants have been watered recently and the soil in the container is well moistened. Choose a cool, cloudy day to transplant or wait until late in the day when the sun is low in the sky. Don't forget to thoroughly water your plants immediately after planting. If you have questions about the best way to handle and transplant seedlings, see this video from the Master Gardener Program of San Luis Obispo County:
https://www.youtube.com/watch?v=72dqbPZFgFY
Give your plants some shade after planting in the garden.
It is difficult to completely avoid damaging a plant's root hairs when transplanting. Root hairs are necessary to take up water and nutrients. Giving your plants some shade in the hottest part of the day for the first 5–7 days after transplanting will help keep them cooler while they regrow their root hairs. Garden shade structures do not have to be complicated and can either be purchased or made at home with items you may already have. Shade cloth, or even the plant flats used for carrying pots can be used. They are easy to set up and can be used year after year. Learn more about shading your plants in this link to a previous blog post:
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=55005
Be sure to look at our Master Gardener Program website to find a wide variety of useful information. Our previous blogs can also be found here: https://ccmg.ucanr.edu/
Help Desk of the UC Master Gardeners of Contra Costa County (SMH)