Growing and harvesting tips for the fall vegetable garden
Soil, seeds, water, nutrients, frosts
Air, water, minerals, and organic matter (living and non-living) are the basic ingredients of all soils. They occur in many combinations. The relative proportions of these ingredients affect how a soil behaves, what kinds of plants will grow in it, and how well they grow.
Whether you’re growing vegetables, herbs and flowers in a clay-based in-ground bed, a raised bed, or in a container, your plants will benefit from the addition of organic matter — COMPOST. If your soil contains too much sand, it will be too fine and drain too fast. Compost will help with that. If your soil contains too much clay, it will be heavy and drain too slowly. Compost will help with that, too. Somewhere in the middle — crumbly, well drained soil — is your goal.
Sow seeds no deeper than 2 times the diameter of the seed, or in the case of oblong seeds, no deeper than 1 to 2 times the length of the seed. (Seeds planted too deep may not germinate.) Fine seed (like carrots) should be sown on the soil surface and then very lightly covered with soil. After sowing, keep the soil consistently moist until seeds germinate and seedlings are well established.
Note: Large seeds (like sugar snap peas) will germinate faster if soaked a few hours in a diluted solution of seaweed before planting.
Be careful not to plant transplants too deep or too shallow. Planting too deep can slow or stop root growth. A too shallow planting may cause roots to dry out. Try to plant so that the top of the root ball is level with the surrounding soil. Soak the soil around new seedlings immediately after transplanting to settle the roots.
Light, Water, Air
Light: Some plants will do ok in part sun, at least 4 hours a day (leafy greens, parsley, cabbage, root crops). Others need 6 to 8 hours to thrive and be productive (broccoli, cauliflower, snap peas). Keep in mind when you’re placing your fall garden that the sun is lower in the sky during the cooler months. Watch the patterns of the sun and shade around your garden before you choose where to plant.
Water: Consistently moist soil will produce the best results, particularly with the more challenging crops like romanesco and cauliflower. Apply enough water to wet the soil to a depth of at least 6 inches. For best crop production, most gardens require about 1 inch of rain or irrigation per week. After a day or two of unseasonably warm weather, check the moisture of the soil in case more water is needed. Poke your fingers into the soil to check. If the top 1 to 2 inches is dry, you need to water.
Air: Although GCP is a big fan of small space, bio-intensive gardening, take care not to space plants too close together. Leaves that are just barely touching is good. Plants with branches and fruits that are overlapping is too close. Plants growing to close together restricts airflow, which can create overly moist conditions that can result in fungal problems.
In addition to adequate light and moisture, your vegetable plants will need nutrients to grow and thrive. Nutrients can come from fertilizers, compost or composted manure.
All parts of a plant need nitrogen for growth—the roots, leaves, stems, flowers and fruits. Nitrogen gives plants their green color. A lack of nitrogen causes the lower leaves to turn yellow and the whole plant to turn pale green. On the other hand, too much nitrogen can kill plants. When vegetable plants are suffering, a little extra nitrogen is often what they need. Compost that includes manure will add nitrogen. Also, fish emulsion and cottonseed.
Phosphorus is needed to help form roots, flowers and fruit. Phosphorus deficiency causes stunted growth and poor flowering and fruiting.
Potassium is needed for overall health of the plant. A potassium shortage shows up in various ways, but stunted growth and yellowish lower leaves are common symptoms.
Note: Before adding commercial fertilizer, it’s a good idea to have your soil tested. A soil test will indicate the levels of nutrients in the soil and will illustrate the amounts of each nutrient to add. If plants are not growing well, fertilizing them will help only if a lack of nutrients is the cause of the problem. For example, plants grown in poorly drained soils or in excessive shade will not be helped by an application of fertilizer. If you need to purchase a fertilizer, GCP recommends that you choose an organic, slow-release fertilizer that’s higher in nitrogen than in phosphorus or potassium, like Microlife 6-2-4.
Top all bare soil with mulch — straw, partially decomposed leaves, partially decomposed wood chips, shredded wood. Mulch helps soil hold moisture longer. It also provides some protection to roots and root vegetables during a hard freeze. Wait until seeds are up or transplants are established before mulching. Do not apply mulch too close to plant stems — keep a couple of inches of space around the stems.
Austin area winters tend to be mild, with a handful of light frosts and maybe one or two short periods of hard freezing temperatures.
In general, a light frost (31-33 degrees) will kill what’s left of your warm weather crops — beans, basil, cucumbers, eggplant, okra, peas, pepper, potatoes, sweet potatoes, squash, and tomatoes, but most of your cool weather crops will be fine.
Colder temperatures (26-30 degrees) may damage some leaves, but usually will not kill broccoli, cabbage, cauliflower, chard, cilantro, dill, lettuce, mustard, onion, radish, and turnip. Beets, carrots, collards, kale, parsley, and spinach generally survive even colder temperatures.
The cold tolerance of vegetables can vary depending on the micro climates in your garden and the prevailing temperatures leading up to a hard freeze. If your broccoli has been growing for a couple of weeks in temperatures ranging from 68 to 88, it may not survive a sudden dip into the low 20s. But broccoli that has adjusted to nights in the 30s should be able to tolerate a hard freeze.
When in doubt, go ahead and protect with row cover or sheets. Be sure to drape the cover so that it’s touching the ground on all sides around the plants. That’s how row covers work — they trap warmer air around the plants. If it’s windy, secure covers with bricks or stakes. As soon as the temperatures are above freezing, remove the cover.
(See particular vegetables below for more specifics on cold tolerance.)
From beets to turnips
You can eat both the greens and the beet roots. Harvest the roots when they’re 3-4 inches in diameter. Use a trowel or small digging fork to loosen the dirt. Then pull out by the bottom of the greens, being careful not to damage the greens. Cut the greens off about 2 inches above the beet and refrigerate separately.
Harvest when central broccoli head is fully formed but before it starts to loosen, turn yellow or flower. Cut it at the base using a sharp knife, leaving about 5-6 inches of stem. You can also harvest the little leaves on the stem — they taste good and they’re very nutritious. After the central head is harvested, side shoots will begin to grow from the stalk. Those shoots will produce small broccoli heads that can be picked as soon as they’re big enough to eat. Frequent harvesting encourages new side shoots to continue forming.
The inner leaves of the cabbage will form a head, which can be harvested any time after it forms. It should feel firm to the touch. If the head starts to crack, harvest immediately. Cut as close to the bottom of the head as possible. Cabbage sprouts may form on the stump of the main head. These can grow to 2-4 inches in diameter and can also be harvested.
This cool weather flower brings bursts of orange and yellow to the fall and spring garden. The blooms are frost tolerant, so calendula usually survives the mild winters of the Austin area. Protect plants from a damaging hard freeze, 25 degrees or below. Calendulas prefer full sun but will also bloom in partial shade. The edible petals add a lovely splash of color when sprinkled over a salad.
Carrots push up out of the soil as they grow, which exposes their crowns to sunlight. The sunlight turns the crowns green. To prevent green crowns — which can be bitter as well as unsightly — keep the crowns covered with soil or mulch throughout the growing season. Loosen soil around carrots with a trowel or digging fork if they’re breaking when you pull them.
Cruciferous Greens (Kale, Collards)
To harvest, snip leaves from the bottom of the stem and allow the growing tip to keep producing new leaves. Leaves harvested the morning after a cold frosty night generally have the best flavor.
Dill planted for a fall garden should do well into November, but will last longer in a mild winter. Dill can survive low temperatures (down to 25 degrees) but will grow better when the soil temperature is about 70 degrees. To harvest, trim leafy fronds as needed.
Plant seeds or transplants into the garden in early October. Harvest the bulb once it’s roughly the size of a tennis ball, which can take from 70 to 90 days. Fennel grows best with consistent moisture and plenty of compost. Fennel survives light frosts, but cover the plant if a hard freeze is coming. To harvest, use a sharp knife and slice the bulb about 2 inches above the tap root, leaving the plant’s growing base intact so it can grow more bulbs. The fennel bulb is crunchy like celery when raw, but with a licorice-like taste that pairs beautifully with chicken, potatoes or tomatoes. Toss thick slices into your chicken roasting pan alongside onions and potatoes. Add slices to a creamy potato gratin. Add chopped fennel when sauteeing onion and garlic to making tomato sauce. It’s also delicious finely sliced into a salad of peppery greens, orange slices, and pecans, and then tossed with a lemon vinaigrette.
Lettuce grows best with consistent moisture. Moisture fluctuations (periods of moist soil followed by dry soil) can cause leaves to become tough and brown tipped, and can contribute to off-flavors. Lettuce leaves can be harvested at any time. Picking the outer leaves (leaving the stem intact) encourages more growth of inner leaves. Heads can be pulled when they reach mature sizes. Leaf lettuces can be harvested using a cut-and-come-again approach — cut the leaves off as needed, but leave the growing stem intact so the plant will grow more leaves and you can keep coming back for more.
Harvest baby mustard green leaves for salads and a spicy addition to sandwiches. Snip the leaves but leave the growing stem to produce more leaves. Harvest larger leaves on more mature plants for steaming or braising. Raw leaves are spicy. Cooked leaves are mild.
Install a trellis or growing cage so pea vines will grow up and away from the soil surface. Pick peas when the pods are crisp and firm and about as long as your little finger. Take care not to damage the vine. Pull gently or snip with clippers. The curly pea tendrils can also be harvested and are quite tasty in salads. Snap peas may be damaged in a light frost, so it’s best to cover. If a hard freeze is coming, cover plants from top to bottom with two layers of row cover.
Smaller turnips often have better texture and flavor, so start picking when the turnip root is 2 inches wide. The flavor of turnips and their greens improves after a light frost so hold off on harvesting if the weather forecasters are predicting a frost. If a hard freeze is coming, pile mulch or leaves around turnips to protect exposed parts from possible damage.